Bumble Bees (Hymenoptera: Apidae) of 
Montana
Authors: Amelia C. Dolan, Casey M. Delphia, Kevin 
M. O'Neill, and Michael A. Ivie
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Annals of 
the Entomological Society of America following peer review. The version of record for (see 
citation below) is available online at: https://dx.doi.org/10.1093/aesa/saw064.
Dolan, Amelia C., Casey M Delphia, Kevin M. O'Neill, and Michael A. Ivie. "Bumble Bees 
(Hymenoptera: Apidae) of Montana." Annals of the Entomological Society of America 110, no. 2 
(September 2017): 129-144. DOI: 10.1093/aesa/saw064.
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
Bumble Bees (Hymenoptera: Apidae) of Montana
Amelia C. Dolan,1 Casey M. Delphia,1,2,3 Kevin M. O’Neill,1,2 and Michael A. Ivie1,4
1Montana Entomology Collection, Montana State University, Marsh Labs, Room 50, 1911 West Lincoln St., Bozeman, MT 59717
(amelia.clare1229@gmail.com; casey.delphia@montana.edu; koneill@montana.edu; mivie@montana.edu), 2Department of Land
Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717, 3Department of Ecology, Montana State
University, Bozeman, MT 59717, and 4Corresponding author, e-mail: mivie@montana.edu
Subject Editor: Allen Szalanski
Received 10 May 2016; Editorial decision 12 August 2016
Abstract
Montana supports a diverse assemblage of bumble bees (Bombus Latreille) due to its size, landscape diversity,
and location at the junction of known geographic ranges of North American species. We compiled the first in-
ventory of Bombus species in Montana, using records from 25 natural history collections and labs engaged in
bee research, collected over the past 125 years, as well as specimens collected specifically for this project dur-
ing the summer of 2015. Over 12,000 records are included, with 28 species of Bombus now confirmed in the
state. Based on information from nearby regions, four additional species are predicted to occur in Montana. Of
the 28 species, Bombus bimaculatus Cresson and Bombus borealis Kirby are new state records. The presence
of B. borealis was previously predicted, but the presence of B. bimaculatus in Montana represents a substantial
extension of its previously reported range. Four additional “eastern” bumble bee species are recorded from the
state, and three species pairs thought to replace one another from the eastern to western United States are now
known to be sympatric in Montana. Additionally, our data are consistent with reported declines in populations
of Bombus occidentalis Greene and Bombus suckleyi Greene, highlighting a need for targeted surveys of these
two species in Montana.
Key words: pollination, Apidae, natural history collection, museum, pollinator
Shrinking ranges and declining populations of wild and managed
bees (Hymenoptera: Apoidea) have recently raised concerns world-
wide (Chaplin-Kramer et al. 2014, Goulson et al. 2015). Hypotheses
have been presented on causes of the observed declines, and predic-
tions have been made about negative economic and environmental
impacts (Holden 2006, Potts et al. 2010, Burkle et al. 2013). Factors
proposed to play a role in population declines of pollinators include
anthropogenic landscape and climate change, lack of high-quality
forage, pathogens and parasites, pesticides, and competition with
and pathogen transfer from nonnative or commercial bees (Winfree
et al. 2009, Goulson et al. 2015, Kerr et al. 2015).
Bumble bees (Bombus spp.) are among the most recognizable
bees due to their large size and colorful bodies. Because they have
the ability to sonicate or “buzz pollinate” certain types of flowers,
they are also some of the most important pollinators for wild and
cultivated plants having poricidal anthers, such as huckleberries
(Ericaceae) and tomatoes (Solanaceae) (Harder and Barclay 1994,
De Luca and Vallejo-Marin 2013). Like other bees, bumble bees
worldwide have experienced declines and range contractions over
the past two decades (Williams and Osborne 2009, Cameron et al.
2011, Goulson et al. 2015). In the United States, Cameron et al.
(2011) used historic records and intensive sampling of present-day
communities to show that four species, Bombus affinis Cresson,
Bombus occidentalis Greene, Bombus terricola Kirby, and Bombus
pensylvanicus (DeGeer), have experienced drastic reductions in their
historic ranges over the past 20–30 yr. Some estimates indicate that
up to 25% of North American bumble bee species are facing some
level of decline (Colla et al. 2012, Williams and Jepson 2014). In
2014, the International Union for Conservation of Nature (IUCN)
Bumble Bee Specialist Group recommended five North American
bumble bee species for “Critically Endangered” status, two for
“Endangered” status, five for “Vulnerable” status, and one for
“Near Threatened” status, while 28 species were considered to be of
“Least Concern” (Williams and Jepson 2014). At least one Bombus
Latreille species in North America, Bombus franklini Frison, known
only from northern California and southern Oregon, may already be
extinct (Williams et al. 2014).
Despite myriad studies focused on varying aspects of bumble bee
biology amid concern over declining populations, large gaps in base-
line knowledge still exist. There may be as many as 250 bumble bee
species worldwide (Williams 1998, Michener 2007), and though
bumble bees are relatively well-known, some regions have been bet-
ter studied than others. In the United States, checklists, range maps,
and population-monitoring studies have been published on the
bumble bees of some states (e.g., Severin 1926, Thorp et al. 1983,
Colla et al. 2011, Scott et al. 2011, Warriner 2012, Koch et al.
2012, Figueroa and Bergey 2015, Tripodi and Szalanski 2015),
whereas other states have few published records.
In the United States, Montana is one of the least-studied areas
with regards to bee species and distribution (Koch et al. 2015),
partly because of a vast, sparsely populated area, much of which is
difficult to access (Montana Wilderness Association 2015). Bumble
bee range maps created using museum data and statistical models
predicted that 25–30 species occur in Montana (Williams et al.
2014). Twenty-seven species have been reported in the literature
(Franklin 1912; Frison 1923; Milliron 1971, 1973a,b; Koch et al.
2012; Williams et al. 2014), but some of these reports are based on
a single locality. Furthermore, <500 specimens have been reported
from the entire eastern half of the state, an area of 190,000 km2
(Williams et al. 2014).
Due to its large size, topographic diversity, and climatic variabil-
ity, Montana supports vegetation zones ranging from relatively low-
elevation, dry plains in the east to boreal and alpine zones in the
west (Lesica 2012). Additionally, the state is at the junction of
known eastern and western North American bumble bee ranges
(Koch et al. 2012). Alpine environments connected to the arctic via
Canada provide a habitat corridor for bumble bee species from the
north, while xeric Great Basin elements approach from the south
(Williams et al. 2014, Discover Life 2016). This diversity of land-
scapes and unique geographic placement make it likely that
Montana contains a large assemblage of bumble bee species that dif-
fers from surrounding states or provinces.
Habitat and landscape changes have been cited as one of the primary
factors threatening bumble bee populations (Williams and Osborne
2009, Goulson et al. 2015). Montana’s history includes disturbances as-
sociated with mining, logging, agriculture, transportation, and recreation
(Burlingame and Toole 1957, Wyckoff 2006). However, before we can
determine if and how bumble bee populations are changing in Montana,
a baseline understanding of the fauna is necessary.
The literature includes records of 27 species of bumble bees col-
lected in Montana since 1883 (Table 1). Four other species (Bombus
bohemicus Seidl, Bombus borealis Kirby, Bombus morrisoni
Cresson, and Bombus ternarius Say) are recorded close to the
Montana border (Williams et al. 2014), and several additional spe-
cies are predicted to be here, based on proximity of neighboring
populations, climatic suitability (sensu Williams et al. 2014), and
geographic considerations (Milliron 1973b; Table 1).
Our objectives were to 1) create an inventory of Bombus spe-
cies in the state, 2) provide county-level distribution data for each
of these species, 3) create a taxonomic key to make identifications
easier and more accurate for those working on Bombus in
Montana, and 4) generate a greatly expanded dataset on the his-
tory, occurrence, and temporal distribution of bumble bees in
Montana. This study was not meant to include ecological or con-
servation assessments, but to provide baseline data to inform fu-
ture research and conservation efforts.
Materials and Methods
Museum and Lab Collections
Our inventory is based on 12,067 specimens of Bombus species
from 25 North American natural history collections or research labs
and four databases (Supp. Table 1 [online only]). The total number
of specimens examined (N¼15,235) was larger because duplicates
from long series of the same species from the same date, place, and
time were examined to check for determination errors, but not every
individual was databased (see Supp. Table 1 [online only]).
All specimens were identified using keys from current literature
(Williams et al. 2014, Koch et al. 2012, Colla et al. 2011, Thorp
et al. 1983, and Stephen 1957). Taxonomy followed Williams et al.
(2014) for all species except Bombus fervidus (F.) and Bombus cali-
fornicus Smith, which we consider to be separate species (see discus-
sion), and Bombus kirbiellus Curtis as separate from Bombus
balteatus Dahlbom, following recent DNA evidence (Williams et al.
2015). New state records, rare species, and difficult-to-identify
specimens were verified by James Strange or Jonathan Koch at the
Bee Biology and Systematics Laboratory (BLCU), Logan, UT, or
Robbin Thorp at the University of California, Davis.
Initially, 3,003 specimens from the Montana Entomology
Collection (MTEC) at Montana State University (MSU) were exam-
ined. Determinations were verified, corrected, or made, and each speci-
men was labeled with a unique identifier tag (barcode). Localities were
georeferenced and verified or corrected, and all records were uploaded
to the MTEC XBio:D database (mtent.org) managed through The
Ohio State University (hol.osu.edu). Additionally, Bombus specimens
deposited in other labs at MSU (Supp. Table 1 [online only]) were ex-
amined, determined, and databased.
Records of Bombus specimens collected in Montana were ob-
tained from the BLCU database, the American Museum of Natural
History (AMNH) database, the Yale University Peabody Museum
of Natural History (PMNH) database, and from Leif Richardson’s
(Williams et al. 2014) database. These records were reviewed and
other North American entomology collections were contacted for
updated lists or loans. Requests for loans were made if there were 1)
new state records, 2) new county records, 3) questionable determi-
nations, 4) range discrepancies, and/or 5) undetermined Bombus
from Montana. Two large, historic collections, the National
Museum of Natural History (NMNH) and the Academy of Natural
Sciences, Philadelphia (ANSP), with specimen data not available
electronically, were visited and Montana specimens were sorted,
identified, and added to the database. For all specimens, we verified
or updated historic determinations, identified undetermined speci-
mens, and added the records to the database.
Field Sampling
Historical data on Bombus from museum specimens revealed that
Montana has been unevenly sampled, with especially low coverage
in the eastern half of the state (Figs. 1–2). In April 2015, the data-
base showed 4 of 56 counties with no Bombus records and 7 others
with <3 species documented. To help remedy this, collecting was
undertaken in the 2015 field season and focused on unsampled or
undersampled regions of Montana. In cooperation with the
Montana Department of Agriculture’s Cooperative Agriculture Pest
Survey (CAPS) program, 30 Japanese Beetle traps (Foley et al. 2011)
and 29 yellow bucket traps (Brambila et al. 2014) were placed in 20
of Montana’s 56 counties from March through August. In addition,
between March and September, we collected bumble bees across the
state, usually on flowers. Bumble bees collected by other labs at
MSU and the U.S. Geological Survey (USGS) in Glacier National
Park were also added to the database. Montana’s County Extension
Agents and Master Gardeners assisted with the project by sending
Bombus specimens collected from various localities in the state.
Specimens were processed using standard procedures (Droege
et al. 2012). Once cleaned, specimens were mounted, identified, and
databased. Data were used to produce county-level range maps and
graphs of each species’ accumulation over time.
Data Analysis
Data were extracted from MTEC XBio:D database into Excel for
analysis. County-level maps were created using a vector graphic
from Wikipedia’s U.S. Counties Map. The vector graphic code was
edited in Adobe Dreamweaver and transferred to Adobe Illustrator
using SVG Crowbar 2 plugin for final editing. The topographical
map was created using Google My Maps. The map was saved as a
PDF and copied into Adobe Photoshop for final editing.
The EstimateS (Colwell 2013) program was used to generate a
Chao1 species richness prediction using each county as a sample.
Species richness predictors estimate the total number of species pre-
sent in a community. The Chao1 estimator is a commonly used spe-
cies richness estimator that is based on the number of rare groups
found in a sample (e.g., singleton taxa and doubleton taxa) to adjust
for the number of species present but not detected by sampling
(Chao 1984, Gotelli and Colwell 2011). It is a lower bound esti-
mate, and often underestimates the true parameter (Chao 1984), but
is considered a good estimator of minimum species richness (Gotelli
and Colwell 2011). A species accumulation curve was also generated
using the EstimateS (Colwell 2013) program. Each county was con-
sidered a sample, and samples were randomized 50 times to create
the mean accumulation curve.
Results
During the study, 12,067 Montana Bombus records were added to the
MTEC XBio:D database. After sampling in all 56 counties (Fig. 3), 28
Bombus species are now known to occur in Montana (Table 2; Fig. 4).
These species include two new state records, Bombus bimaculatus
Table 1. Summary of literature records of Bombus from Montana
Citation Bombus species documented
Morrill 1903 Recorded: Bombus atrifasciatus Morrilla, Bombus cooleyi Morrillb, Psithyrusc latitarsus Morrilld, Psithyrus insularis
Franklin 1912 Recorded: B. appositus, B. centralis, Bombus edwardsii Cressone, B. fervidus, B. flavifrons, B. huntii, B. kirbyellusf, B. mix-
tus, B. nevadensis, B. occidentalis, B. rufocinctus, Bombus separatus Cressong, B. vagans, Psithyrus consultus Franklinh,
P. insularis, P. latitarsusd
Predicted: B. californicus, B. frigidus, B. melanopygus, B. pensylvanicus, B. sitkensis, Psithyrus tricolor Franklini
Franklin 1915 Recorded: B. californicus
Anonymous 1920 Recorded: B. bifarius, B. centralis, B. occidentalis, B. rufocinctus (Species not listed in publication, but specimens are
deposited at the Academy of Natural Sciences, Philadelphia)
Frison 1923 Recorded: B. ternarius, B. terricola, B. vosnesenskiij
Kral 1955 Recorded: B. edwardsiie, B. occidentalis, B. ternarius, B. terricolak
Milliron 1971 Recorded: B. nevadensis, B. occidentalis
Predicted: B. auricomus, B. terricola
Milliron 1973a Recorded: B. appositus, B. fervidus fervidus
Predicted: B. fervidus californicus, B. kirbyellusf, B. pensylvanicus
Milliron 1973b Recorded: B. griseocollis
Predicted: B. morrisoni
Hurd 1979 Recorded: B. nevadensis auricomus, B. sitkensis, B. ternarius, B. terricola terricola, B. vagans vagans
Bauer 1983 Recorded: B. appositus, B. bifarius nearcticus, B. flavifrons, B. frigidus, B. kirbyellusf, B. melanopygus, B. mixtus, B. neva-
densis nevadensis, B. occidentalis, B. sylvicola, P. insularis
O’Neill et al.1991 Recorded: B. griseocollis, B. nevadensis nevadensis, B. rufocinctus
Fultz 2005 Recorded: B. appositus, B. californicus, B. edwardsiie, Bombus fernaldae (Franklin)i, B. fervidus, B. flavifrons, B. impa-
tiensj, B. insularis, B. melanopygus, B. mixtus, B. occidentalis, B. rufocinctus, B. suckleyi
Pearce et al. 2012 Recorded: B. centralis, B. fervidus, B. griseocollis, B. huntii, B. rufocinctus, B. sp.
Koch et al. 2012 Recorded: B. appositus, B. bifarius, B. californicus, B. centralis, B. fernaldaei, B. fervidus, B. flavifrons, B. frigidus, B. gri-
seocollis, B. huntii, B. insularis, B. melanopygus, B. mixtus, B. nevadensis, B. occidentalis, B. rufocinctus, B. sitkensis,
B. suckleyi, B. sylvicola, B. vagans
Predicted: Bombus balteatus Dahlboma, B. morrisoni, B. ternarius, B. terricola
Simanonok and
Burkle 2014
Recorded: B. appositus, B. balteatusa, B. bifarius bifarius, B. bifarius nearcticus, B. centralis, B. fernaldaei, B. flavifrons, B.
frigidus, B. insularis, B. melanopygus, B. mixtus, B. nevadensis, B. sylvicola
Williams et al. 2014 Recorded: B. appositus, B. balteatusa, B. bifarius, B. centralis, B. fervidus, B. flavidus, B. flavifrons, B. frigidus, B. griseo-
collis, B. huntii, B. insularis, B. melanopygus, B. mixtus, B. nevadensis, B. occidentalis, B. pensylvanicus, B. rufocinctus,
B. sitkensis, B. suckleyi, B. sylvicola, B. terricolak, B. vagans
Recorded Near Montana Border: B. bohemicus, B. borealis, B. morrisoni, B. ternarius
Predictedl: B. bohemicus, B. borealis, B. cryptarum, B. fraternus, B. morrisoni, B. ternarius, B. vosnesenskii
a B. atrifasciatus¼B. balteatus (sensu Hurd 1979, sensu Williams et al. 2014)¼B. kirbiellus Curtis (Williams et al. 2015).
b B. cooleyi¼B. bifarius (Hurd 1979).
c The genus Psithyrus is considered to be a subgenus of Bombus (Williams 1998).
d P. latitarsus¼B. suckleyi (Hurd 1979).
e B. edwardsii¼B. bifarius (Frison 1923) or B. melanopygus (Owen et al. 2010).
f Bombus kirbyellus is an unjustified emendation of B. kirbiellus Curtis (Williams et al. 2015).
g B. separatus¼B. griseocollis (Hurd 1979).
h P. consultus¼B. insularis (Williams et al. 2014).
i P. tricolor¼B. fernaldae (sensu Hurd 1979)¼B. flavidus (sensu Williams et al. 2014).
j This record is not verified, see discussion.
k Likely B. occidentalis, see discussion.
l Predicted via climatic suitability maps.
Cresson and B. borealis. Seven of the 28 are typically considered to
have “eastern” United States ranges (Koch et al. 2012): Bombus auri-
comus (Robertson), B. bimaculatus, B. borealis, B. pensylvanicus, B.
ternarius, B. terricola, and Bombus impatiens Cresson. The last is an
eastern species that is reared for commercial purposes (see discussion
for more details about its presence in Montana). Bombus vosnesenskii
Radoszkowski is not included in our species list because no specimen
from Montana could be found to verify Frison’s (1923) literature
record.
The mean species accumulation curve generated with the
EstimateS program (Colwell 2013) reaches an asymptote at 28 spe-
cies (Fig. 5). Additional analysis with the EstimateS program
(Colwell 2013) yielded a Chao1 mean prediction of 28 species of
Bombus for Montana (SD¼0.12; 95% confidence interval¼28.0–
28.2 species). The variation in sampling methodology by many indi-
viduals over the past 130 yr, as well as the uneven spatial and tem-
poral distributions of sampling prevents quantitative analyses of
diversity and abundance comparisons by region. Nevertheless, the
distribution maps (Fig. 4) and numbers of specimens per species pre-
sented here (Table 2) can provide insights into the relative abun-
dance and ranges of Bombus species in Montana. It seems clear that
species vary in abundance in the state as a whole. Of the 28 species,
just 4 are represented by >1,000 specimens (Table 2). For another
16, >100 specimens are in the database, but just 10 or fewer speci-
mens were available for 4 species.
The oldest Montana specimens in the dataset were collected in
1883 (four individuals, NMNH). Sixty-three percent of the records
in the database were collected between 1990 and 2015. The greatest
accumulation of specimens (over 3,000) came in 2015, mostly from
the current project. For a full discussion of the history of Bombus
collecting in Montana, see Dolan (2016).
The intensive 2015 sampling did not uncover any new state re-
cords. There were, however, 113 new county records. Moreover,
sampling in 2015 increased sample sizes and added species records
for previously undersampled localities (Figs. 1–2). Excluding new re-
cords (where the divisor would be zero), increase in specimens per
species from April 2015 to January 2016, ranged from 0% for the
special case of the introduced B. impatiens and 27% for native spe-
cies B. sitkensis, to 900% for B. terricola, with a mean increase of
146% for the 27 native species.
Discussion
Bumble bee records are now available for all 56 of Montana’s coun-
ties. The number of Bombus specimens collected in the state has
greatly increased since 2000 due, not only to the sampling effort as-
sociated with the current project, but also to the general increase in
pollinator research projects in Montana over the past 15 yr (e.g.,
Fultz 2005, Cameron et al. 2011, Pearce et al. 2012, Simanonok and
Burkle 2014). With the exception of two species, B. occidentalis and
Bombus suckleyi Greene, all species have experienced at least a
49% increase in the number of specimens known from Montana
since 2000.
Of the two new state records, B. borealis had previously been
documented in Alberta and Saskatchewan, just north of Montana’s
border and just east of the state in North Dakota. Its presence in
Montana was predicted, but never confirmed (Williams et al. 2014).
The presence of B. bimaculatus is of special note because this species
had previously not been documented or even predicted to be west of
the eastern Dakotas and Nebraska (Williams et al. 2014). The dis-
covery of this species in Montana represents a substantial westward
extension of its known range.
Additional sampling is still needed to fully document the range
and diversity of Bombus species in Montana since >50% of
Montana’s counties (29/56) currently have <100 Bombus records
Fig. 1. Number of Bombus specimen records per Montana county in April
2015 (A) and January 2016 (B). White¼0; light gray¼1–10; medium
gray¼11–100; dark gray¼101–1,000; black >1,000.
Fig. 2. Number of Bombus species records per Montana county in April 2015
(A) and January 2016 (B). White¼0–3; light gray¼4–8; medium gray¼9–12;
dark gray¼13–17; black¼18–22.
(Table 2) and two counties only have 12 records. The entire state
presents a diversity of habitat types, vegetation, and elevations that,
if sampled more completely, could provide additional insights into
state and North American range and population trends and might
also reveal the presence of additional species.
The Influence of Sampling Effort
Geographic variation in past sampling effort is certainly a factor in
interpreting the data presented here. The counties where entomol-
ogists have conducted research projects not necessarily focused on
survey work (e.g., Gallatin, Flathead, Carbon, and Meagher) have
the most species (Fig. 2). Additionally, the map of collection sites
in Montana (Fig. 3) matches up well with the state’s major high-
ways, indicating that much of the historical sampling of Bombus
has been convenience sampling. Also, at least two of the projects
that contributed data targeted limited subsets of Bombus species
(O’Neill et al. 1991, Cameron et al. 2011), which may have
skewed our relative abundance data for their targeted species.
O’Neill et al. (1991) preferentially collected Bombus griseocollis
(DeGeer), Bombus nevadensis Cresson, and Bombus rufocinctus
Cresson. Cameron et al. (2011) did the same for Bombus bifarius
Cresson and B. occidentalis. Thus, the number of these species in
our data set may not accurately reflect their actual relative abun-
dance in the communities sampled. Furthermore, collecting in
Lincoln and Sanders Counties in 2014 was part of a study focusing
on insects associated with the huckleberry plant (Vaccinium globu-
lare Rydberg; Dolan 2016). Bumble bees were only collected in
specific habitats from V. globulare, so these counties in northwest
Montana almost certainly have more Bombus species than the
data suggest.
Unrecorded Bombus Potentially Present in Montana
The Chao1 mean prediction of 28 Bombus species in Montana
(Fig. 5) indicates that we are unlikely to find more species than we
have already documented. However, based on proximity of neigh-
boring populations, climatic suitability (sensu Williams et al.
2014), and geographic considerations (Milliron 1973b), there are
four Bombus species not yet recorded from Montana that may still
be found. One of these is Bombus cryptarum (F.), whose range is
recorded as the tundra/taiga regions of the northern Rocky
Mountains from Alaska through southwestern Canada and across
northwestern Canada to the Hudson Bay (Williams et al. 2014).
The Canadian Rocky Mountains provide a continuous alpine envi-
ronment south into northwestern Montana, allowing for the possi-
bility of the occurrence of B. cryptarum. Records from Canada
show this species has been collected within 20 km of Montana’s
northern border near Milk River, Alberta (Ashton Sturm, personal
communication, specimens in Jessamyn Manson Lab Collection,
University of Alberta).
Predictive habitat suitability maps extend the possible range of
B. morrisoni from the deserts in the southwestern United States to
the dry scrubland regions of southwestern Montana (Williams et al.
2014). There are records of this species in parts of Idaho near
Montana, including one from Salmon, ID, just 17 km southwest of
the border (Discover Life 2016). There are also records of B. morri-
soni in southern Wyoming (Williams et al. 2014, Discover Life
2016); thus, it is possible that the range of B. morrisoni extends into
southwest Montana (e.g., Beaverhead County).
Bombus bohemicus has been recorded from New England across
the Midwestern United States and then north and west across west-
ern Canada to Alaska (Williams et al. 2014). It has not been docu-
mented from Montana, but there are records just to the north in
Alberta and Saskatchewan, Canada (Williams et al. 2014). This spe-
cies is very similar to B. suckleyi, which is also in the subgenus
Psithyrus and is thought to replace B. bohemicus in parts of the
West (R. Thorp, personal communication). Montana, especially
northeastern Montana, is a place where the ranges of these two spe-
cies may overlap, though both of these species are apparently in de-
cline (Williams et al. 2014).
None of the published predictive maps extend the possible range
of Bombus perplexus Cresson into Montana (Williams et al. 2014).
However, there are records of B. perplexus collected across the east-
ern United States to Minnesota (Williams et al. 2014), and we added
a record from Calgary, 225 km north of the Montana border
(Museum of Zoology, University of Calgary (BDUC) #MTEC
019296). This distribution pattern, which is similar to B. borealis
Fig. 3.Map of localities where Bombus specimens in Montana have been collected from 1883–2015. Map data 2016 Google, INEGI Imagery 2016 TerraMetrics.
Table 2. The 28 Bombus species occurring in Montana, organized alphabetically by species
Species Earliest specimen (Year) First literature record Total no. of specimens Total no. of counties
Bombus (Subterraneobombus) appositus 1899 Franklin 1912 302 25
Cresson, 1878
Bombus (Bombias) auricomus 1971 Hurd 1979 5 4
(Robertson, 1903)
Bombus (Pyrobombus) bifarius 1883 Morrill 1903 1,911 37
Cresson, 1878
Bombus (Pyrobombus) bimaculatus 2011 New State Record 18 7
Cresson, 1863
Bombus (Subterraneobombus) borealis 1926a New State Recordb 20 8
Kirby, 1837
Bombus (Thoracobombus) californicus 1913 Franklin 1915 91 19
Smith, 1854
Bombus (Pyrobombus) centralis 1901a Franklin 1912 641 47
Cresson, 1864
Bombus (Thoracobombus) fervidus 1899a Franklin 1912 688 47
(F., 1798)
Bombus (Psithyrus) flavidus 1929b Fultz 2005 158 19
Eversmann, 1852
Bombus (Pyrobombus) flavifrons 1900 Franklin 1912 488 30
Cresson, 1863
Bombus (Pyrobombus) frigidus 1929 Bauer 1983 59 9
Smith, 1854
Bombus (Cullumanobombus) griseocollis 1904 Franklin 1912 357 38
(DeGeer, 1773)
Bombus (Pyrobombus) huntii 1883a Franklin 1912 1,840 53
Greene, 1860
Bombus (Pyrobombus) impatiens 1980 Fultz 2005c 7 2
Cresson, 1863
Bombus (Psithyrus) insularis 1899 Morrill 1903 389 30
(Smith, 1861)
Bombus (Alpinobombus) kirbiellus 1900 Morrill 1903 122 7
Curtis, 1835
Bombus (Pyrobombus) melanopygus 1913 Franklin 1912 379 19
Nylander, 1848
Bombus (Pyrobombus) mixtus 1900 Franklin 1912 855 30
Cresson, 1878
Bombus (Bombias) nevadensis 1899a Franklin 1912 252 41
Cresson, 1874
Bombus (Bombus) occidentalis 1899a Franklin 1912 1,046 41
Greene, 1858
Bombus (Thoracobombus) pensylvanicus 1964 Williams et al. 2014 5 4
(DeGeer, 1773)
Bombus (Cullumanobombus) rufocinctus 1899 Franklin 1912 1,391 52
Cresson, 1863
Bombus (Pyrobombus) sitkensis 1934b Hurd 1979 180 8
Nylander, 1848
Bombus (Psithyrus) suckleyi 1899 Morrill 1903 146 19
Greene, 1860
Bombus (Pyrobombus) sylvicola 1913 Bauer 1983 187 18
Kirby, 1837
Bombus (Pyrobombus) ternarius 1931a Frison 1923 301 18
Say, 1837
Bombus (Bombus) terricola 2011a Frison 1923d 10 2
Kirby, 1837
Bombus (Pyrobombus) vagans 1901 Franklin 1912 152 18
Smith, 1854
a Some specimens at ANSP have no recorded collection date. They were determined by Franklin in 1922, and may be part of E.T. Cresson’s collection, which
means they may have been collected as early as the mid-18th century (J. Weintraub personal communication).
b This species was predicted, but not confirmed, by earlier literature to be in Montana.
c This record of B. impatiens could not be verified. See text.
d The specimen recorded by Frison (1923) is likely B. occidentalis. See text.
Fig. 4. (a–ab). County-level distribution maps for the 28 Bombus species known to occur in Montana. Note that the map of B. impatiens, Figure 4n, is documenting
1) the presence of bees introduced for research in Chouteau County and 2) a distribution outlier in Ravalli County. See text for details.
Fig. 4. (a–ab). Continued.
and B. ternarius, may suggest the presence of B. perplexus in the
northeastern part of Montana.
Sympatry of Eastern/Western Species Pairs
In North America, there are several morphologically similar species
thought to have ranges that are geographically distinct (i.e., one spe-
cies is said to be “eastern”, the other “western”; Colla et al. 2011,
Koch et al. 2012, Williams et al. 2014). This geographic distinction
is often used to aid in species diagnosis. The division between east-
ern and western North America is often split at the 100th meridian,
but that separation is relatively arbitrary. Because Montana’s east-
ern border is near the 100th meridian, eastern Montana is one area
where eastern and western species ranges may overlap. This project
has confirmed the sympatric occurrence of three of these species
pairs: B. auricomus/B. nevadensis, Bombus huntii Greene/B. ternar-
ius, and B. occidentalis/B. terricola.
Bombus auricomus/Bombus nevadensis
Throughout their taxonomic histories, B. nevadensis and B. aurico-
mus have been considered either separate species or subspecies
(Hurd 1979). Currently, they are considered separate species, with
B. nevadensis occurring in western North America and B. auricomus
in the East (Williams et al. 2014). Bombus nevadensis is considered
common throughout its range (Koch et al. 2012) and is widespread
in Montana (252 specimens in 41 counties; Fig. 4s). On the other
hand, the presence of B. auricomus in Montana was uncertain prior
to this study, though its occurrence here was predicted by Milliron
(1971). Bombus auricomus is a common eastern species known to
occur throughout eastern temperate forests west to the Great Plains
(Williams et al. 2014). We documented five specimens of B. aurico-
mus in four Montana counties reaching as far west as Pondera
County (Fig. 4b). These records extend the known range of B. auri-
comus west to the foothills of the Rocky Mountains (111.506 W),
and suggest an extensive area of B. auricomus/B. nevadensis sym-
patry across the eastern two-thirds of Montana (compare Fig. 4b
and Fig. 4s).
Bombus huntii/Bombus ternarius
Bombus huntii and B. ternarius are morphologically similar, but
they have been thought to be geographically distinct. Bombus huntii
is said to replace B. ternarius in the interior western United States,
while B. ternarius replaces B. huntii in the North (Williams et al.
2014). Across much of Montana, however, these two species occur
sympatrically (compare Fig. 4m and Fig. 4z). In Montana, B. huntii
is one of the most common and widespread species. The earliest
specimen was collected in 1883, and it has been consistently col-
lected since that time across the entire state (Fig. 4m). Conversely,
only six specimens of B. ternarius were collected before 2008 and
added to the database. However, since 2011, when the Montana
Department of Agriculture began using bucket traps to monitor
for invasive pests in eastern Montana, many more individuals of
B. ternarius have been collected, and it has become one of the
most commonly collected species in the northeastern portion of
the state (Fig. 4z).
Bombus occidentalis/Bombus terricola
The range of B. occidentalis is extensive across western North
America (Williams et al. 2014), and this species was once one of the
most common bees in the West. However, since the 1990s, some
populations have experienced sharp declines (Cameron et al. 2011,
Williams et al. 2014). Bombus terricola is an eastern and northern
North American species (Williams et al. 2014), known to be in the
Black Hills area of South Dakota (Koch et al. 2012) and predicted
to be as far west as eastern Montana (Milliron 1971, Koch et al.
2012, Williams et al. 2014). It has been collected in Alberta east of
Edmonton, and in northwestern Alberta near Valleyview and
Grande Prairie (A. Sturm, personal communication). These two spe-
cies are thought to be geographically distinct with B. occidentalis
replacing B. terricola in the West. Literature records placed B. terri-
cola in multiple locations across Montana (Frison 1923, Kral 1955,
Williams et al. 2014). However, upon examination of many of the
specimens associated with those records, nearly all of the B. terricola
records from Montana are B. occidentalis according to current
Fig. 5. Species accumulation curve and Chao 1 mean for Bombus in Montana. Figure was generated using EstimateS (Colwell 2013). Each county was considered
a sample and samples were randomized 50 times to create the mean accumulation curve.
taxonomic understanding (Koch et al. 2012, Williams et al. 2014).
We did collect nine specimens of B. terricola from far northeastern
Montana (MTEC): one from 2011 and eight in 2015 (Fig. 4aa).
There is one more verified B. terricola specimen determined by
Franklin in 1922 (ANSP), but it lacks a date or specific locality.
Bombus occidentalis has been collected in 41 Montana counties
(Fig. 4t), but has not yet been collected in the southeastern-most re-
gion of Montana, where B. terricola is also likely to be found.
However, we now have records of these two species being sympat-
ric, at least in the two northeastern-most counties of Montana (com-
pare Fig. 4t and Fig. 4a).
Taxonomic Challenges
When it comes to identifying bumble bees, a frequently documented
challenge is the extraordinary intra- and interspecific variation in
the color patterns of the hair-like setae (hereafter referred to as
hairs) occurring among members of a species (Milliron 1971,
Williams 1998, Owen et al. 2010). This difficulty is exacerbated by
the tendency of multiple species to converge on similar color pat-
terns when occupying similar geographic locations (Williams 1998).
Recent DNA evidence confirms that species can be extremely diffi-
cult (or even impossible) to identify by morphological characters
alone, as there appears to be phenotypic convergence of genetically
distinct species (Williams 2007, Koch 2015). In Montana, especially
western Montana with its elevational diversity, the variation in color
patterns is accompanied by noticeable differences in hair length and
texture (Milliron 1971, A.C.D., unpublished data), making iden-
tification even more challenging. For the species pairs described
below, characters use to distinguish between similar species are
for females only. Male determination requires examination of
genitalia (see Williams et al. 2014 for more information on identi-
fication of males).
Bombus auricomus/Bombus nevadensis
As discussed above, B. auricomus and B. nevadensis are morphologi-
cally similar species that were thought to be geographically distinct.
Both occur in Montana, and distinguishing between them using mor-
phological characters is extremely difficult. The main morphological
character used to tell these species apart is the presence or absence of
a black interalar band. Bombus auricomus typically has a strong
black interalar band, while B. nevadensis usually has yellow hairs pre-
dominating dorsally on the mesosoma with only a circle of black hairs
medially. Another diagnostic character used is the size and spacing of
punctations between the eyes and the ocelli (Williams et al. 2014),
but the very subtle spacing differences make this character difficult.
Some individuals are especially difficult to distinguish because the cir-
cular patch of black hairs on B. nevadensis is expanded into a nearly
complete interalar band, more closely resembling B. auricomus,
though this color variant is most common on the West Coast of the
United States. For this study, we relied on a complete black interalar
band as diagnostic for B. auricomus. Therefore, if the black hairs on
the thorax extended to the wing bases, even if there were a few yellow
hairs intermixed, we determined the specimen to be B. auricomus. If,
however, most of the hairs touching the wing bases were yellow, we
determined it to be B. nevadensis.
Bombus huntii/Bombus ternarius
As discussed above, B. huntii and B. ternarius are morphologically
similar species previously thought to be geographically distinct.
However, because they occur sympatrically across much of
Montana, geographic location cannot be used to aid determinations.
Key morphological characters, however, can be used to tell these
two species apart. Bombus ternarius has black hairs on the face with
yellow hairs located centrally near the antennal bases, and the yel-
low hairs on the scutellum are divided by a line or triangle of black
hairs. Often there are also yellow hairs on the front coxae. In B.
huntii, the yellow hairs of the scutellum are not divided by black,
the hairs on the face are predominantly yellow, and the hairs on the
coxae are completely black.
Bombus occidentalis/Bombus terricola
As discussed above, B. terricola and B. occidentalis were thought to
be geographically separated as eastern and western North American
species, but both occur in Montana. For these two species, key mor-
phological characters can be used for determination. Bombus terri-
cola has metasomal T2 (T¼ tergite) entirely yellow while B.
occidentalis always has at least some black on T2.
Bombus californicus/Bombus fervidus
Bombus fervidus is a widespread species that has been collected trans-
continentally in North America while B. californicus is a western spe-
cies known from the Pacific Coast to the Rocky Mountains (Koch
et al. 2012, Williams et al. 2014). Historically, there has been diffi-
culty distinguishing between certain forms of B. californicus and
B. fervidus (Stephen 1957), and the two have been considered synony-
mous by some (Milliron 1973a, Williams et al. 2014). However,
where the two species are sympatric, B. fervidus occurs mostly in the
prairies, whereas B. californicus occurs in forested foothills (Thorp
et al. 1983). New molecular data provide further evidence that the
two are distinct species, though they can be phenotypically conver-
gent (Koch 2015). Based on this, we treat them as separate species in
Montana. The two appear to be sympatric in the western counties,
though our collection sites and observations support the ecological
distinction. Bombus fervidus is widespread in the prairie-type habitats
of eastern Montana and was collected all across the state to the west-
ern border. Bombus californicus was collected only in the mountain-
ous regions of western Montana (compare Fig. 4f and Fig.4h).
Bombus californicus has several different color morphs, some
more cryptic than others. Metasomal T4 is always yellow, as in
B. fervidus, while T1–T3 are variable in color. Some forms have
T1–T3 completely black while others have T1–T3 almost com-
pletely yellow with only small patches of black laterally on T2.
Identification is complicated by a spectrum of intermediate color
patterns between these two extremes (Williams et al. 2014, Koch
2015). Based on our observations, B. fervidus in Montana have only
yellow hairs on T1–T4.
Bombus centralis/Bombus flavifrons
Certain individuals of B. centralis are very similar to B. flavifrons.
Both species have a longer-than-wide malar space and a hair pattern
of metasomal T1: yellow, T2: yellow, T3: orange, and T4: orange.
The key morphological character that separates these two is the
amount of black hair intermixed with yellow on the anterior scu-
tum. However, this character is not often clear-cut. In fact, the
blending of diagnostic characters occasionally makes separation im-
possible (Stephen 1957, A.C.D., unpublished data). Some individ-
uals can easily be identified as one species or the other, but in many
cases there appears to be more of a spectrum of B. centralis–B. flavi-
frons than two distinct species groups. In general, B. flavifrons is
found in more forested, montane areas, while B. centralis is found
more in the plains and valleys (Thorp et al. 1983; Fig. 4g and j;
A.C.D., unpublished data). Because these habitats often overlap in
Montana, the species also occur in both habitats.
We used the amount of black hairs on the anterior scutum and
the general length of the body hairs as our main diagnostic charac-
ters. If only a few black hairs were intermixed on the anterior scu-
tum and the body hairs were generally short and even, we identified
the specimen as B. centralis. If more than just a few hairs were inter-
mixed on the anterior scutum and the hairs were generally longer
and more uneven, we identified the specimen as B. flavifrons. If an
identification of B. centralis or B. flavifrons was not obvious, we de-
faulted to an identification of B. flavifrons, following the recommen-
dation of James Strange at the BLCU in Logan, UT. A few especially
difficult specimens were identified only as Bombus sp. with a note
indicating the specimen was either B. flavifrons or B. centralis.
Species Introduced to Montana
Bombus impatiens is a common eastern North American species
whose native range extends only as far west as Nebraska and
Minnesota (Williams et al. 2014). It has been commercially reared
for greenhouse pollination services and research since the 1980s
(Koppert Biological 2015). Concerns have been raised about the
transport of this species to the western United States and the possible
consequences for native bees if feral B. impatiens colonies become
established outside of their native range (Xerces Society et al. 2013).
Commercial hives contain queen excluders in order to prevent the
escape of new queens and the establishment of feral colonies (Planet
Natural 2016). Still, the use of these colonies is of some concern,
with potential consequences including the development of feral colo-
nies by escaped queens, pathogen spillover (McMahon et al. 2015),
and competition with native pollinators (Potts et al. 2010, Morales
et al. 2013, Graystock et al. 2016).
There was one record of this species in Montana from a 2005
study (Fultz 2005), but this record could not be validated because
the specimen could not be located.
The database currently contains seven specimens of B. impatiens
from Montana (Fig. 4n). One verified specimen of B. impatiens was
collected in Ravalli County in June of 1980 from a locality on the
western side of the continental divide, well beyond the known range
of B. impatiens and before the widespread use of B. impatiens as a
commercial pollinator (Snow Entomological Museum Collection,
University of Kansas, SEMC). The other six specimens of B. impa-
tiens are from a research project using commercially reared B. impa-
tiens in a comparison between organic and conventional wheat
fields in Chouteau County. These six records were added to the
database as documentation in case feral colonies of this species are
detected in that region in the future. At the end of the summer 2014
field season, individuals of B. huntii were found inside these com-
mercial B. impatiens colonies (MTEC 019701, MTEC 019702),
documenting that native and commercially reared bees are inter-
acting in the wild, providing a potential pathway for pathogen
and parasite transfer from imported colonies to native bees
(Graystock et al. 2016).
Species Possibly in Decline
The purpose of our project was to provide baseline data and general
distribution data for Bombus species occurring in Montana. We did
not attempt to use these data to form conclusions about population
trends or changes in historic ranges. Still, our results show that, of
the 28 species collected, records for all but two experienced an in-
crease of49% since 2000 when sampling efforts in Montana sub-
stantially increased. The increase in records of B. occidentalis is just
36% since 2000, and only five individuals of B. suckleyi have been
added to the database since 2000 (MTEC, BLCU, KMOC), repre-
senting only a 4% increase. These relatively low percentage in-
creases are consistent with reported population declines for these
species (Cameron et al. 2011; Hatfield et al. 2015a,b; Koch et al.
2015).
Changes in the prey composition of natural enemies over the
past 50 yr may also be reflective of population declines in B. occi-
dentalis. Armitage (1965) found B. occidentalis to be the most com-
mon prey (35% of 203 Bombus spp.) of the wasp Philanthus
bicinctus Mickel at a site on the southern edge of Yellowstone
National Park (50 km south of Montana). Forty years later, how-
ever, Dukas (2005) found that B. rufocinctus was the primary prey
of the wasp at the same site, though he does not indicate whether B.
occidentalis was among the remaining prey.
It has been hypothesized that the decline of B. suckleyi is associ-
ated with the observed decline of B. occidentalis, its primary host
(Hatfield et al. 2015b). In Montana, which is at the center of the his-
toric range of B. occidentalis (Cameron et al. 2011), there has not
been a great deal of concern about populations declining. Because of
this, the low number of B. suckleyi collected in the past 15 yr ini-
tially seemed a bit surprising. No standardized population assess-
ment has yet been conducted in Montana, so it is not appropriate at
this time to form conclusions about the populations of any of
Montana’s species. However, it is clear that more work is needed to
assess the true range, status, and habits of both B. suckleyi and its
primary host, B. occidentalis, in Montana.
Notes on Sampling Methods
Many of the bumble bees collected in Montana over the past 130 yr
and examined for this project were captured using a net. However,
other methods were also used to obtain specimens, including pan
traps, pitfall traps, flight intercept traps, bucket traps, and Japanese
beetle traps. In most cases, the bumble bees collected by these traps,
excluding pan traps, would be considered “by-catch,” because they
are commonly used to sample non-Hymenopteran taxa. Typically,
nontarget species collected in these traps are stored but not pro-
cessed, or discarded. Even the small and biased samples of nontarget
bee species collected by nontraditional trapping methods provide
valuable insights when added to larger specimen and literature data-
bases (Hung et al. 2015, Spears and Ramirez 2015). In our study,
by-catch provided samples from a variety of localities throughout
Montana that may not otherwise have been represented (e.g. Ivie
et al. 1998, Winton 2010).
Because bucket and Japanese beetle traps are extremely effec-
tive at attracting bumble bees, their use is very enticing. We advise
that anyone utilizing these traps in the future should exercise cau-
tion and deploy them at very low densities since the large number
of bees captured could drastically reduce populations of nearby
colonies. Due to limitations in time and travel, our 2015 traps
were set up in May and left up throughout the summer.
Consequently, all castes of bees were collected, including a large
number of queens. We would caution against using these traps
early in the spring or summer and late in the summer when queens
are active, since the capture of queens compared to workers poten-
tially has a much greater impact on colony establishment. In addi-
tion, because the yellow color and floral scents used as lures in
Japanese beetle and bucket traps make them highly attractive to
bees, we encourage the development of alternative trap colors and
lures that effectively collect target species while avoiding the un-
necessary capture of nontarget pollinators.
Key to Female Bumble Bees of Montana
(Adapted From Koch et al. 2012 With Additional
Notes FromWilliams et al. 2014)
The following key is to female bumble bees only. To identify
males, we recommend Bumble Bees of North America
(Williams et al. 2014). The key includes all 28 species recorded
from Montana along with four species that might be found
here. Morphological characters used in the key are shown
in Figure 6. When color is used in the key, it refers to the
color of the hair-like setae (referred to as “hairs”) unless other-
wise stated.
Fig. 6. (A–C). Morphological characters used to identify female Bombus to species.
One of the most challenging characters used to identify bum-
ble bees is the length of the malar space compared to its width.
The length of the malar space is measured from the lower mar-
gin of the compound eye to the mandibular hinge. The width of
the malar space is measured from the edge of the anterior man-
dibular hinge to the posterior hinge (Fig. 6b). This character is
best viewed in profile. In general there are three malar-space
lengths: 1) shorter than wide, 2) as long as wide, and 3) longer
than wide. There is considerable variability within these catego-
ries, and it takes practice to learn to identify these with
confidence.
Detailed species accounts, along with a summary of key diagnos-
tic characters can be found on the Montana Entomology Collection
website (Dolan et al. 2016) and in Dolan (2016).
1. Female: antenna with 12 antennomeres; metasoma with six
visible tergites................................................................... .2
1’. Male: antenna with 13 antennomeres; metasoma with seven
visible tergites. No key provided. (To key males to species,
use Williams et al. 2014.)
2(1). Outer surface of hind tibia concave and shiny; corbicula pre-
sent; social species .............................................................3
2’. Outer surface of hind tibia convex and hairy; corbicula ab-
sent; social parasites.........................................................35
3(2). T2 and T3 with red or orange hairs, sometimes with yellow
hairs intermixed at least medially .......................................4
3’. T2 and/or T3 with yellow or black hairs ..........................10
4(3). Scutum anterior to wing bases with yellow and black hairs
intermixed, giving cloudy appearance ................................5
4’. Scutum anterior to wing bases with predominantly yellow or
pale yellow hairs ................................................................6
5(4). T2 with black hairs at least medially; integument of hind leg
basitarsus brownish-orange and often lighter than the tibia;
corbicular fringes orange or brown. . .. . .. . .. . .. . . . . .. . .. . .. . .
. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .Bombus bifarius Cresson
5’. T2 orange; hind tibia and basitarsus concolorous; corbicular
fringes black, sometime with orange tips. . .. . .. . .. . .. . .
. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....Bombus melanopygusNylander
6(4’). Malar space distinctly shorter than wide; face with predomi-
nantly black hairs ....................Bombus rufocinctus Cresson
6’. Malar space as long as wide; face with yellow hairs, at least
centrally ............................................................................7
7(6’). Scutellum with yellow hairs only ...... Bombus huntii Greene
7’. Scutellum with yellow or pale yellow hairs divided by a line
or triangle of black hairs....................................................8
8(7’). T2 color variable, but with black hairs at least medially;
integument of hind leg basitarsus brownish-orange and
often lighter than the tibia ............ Bombus bifarius Cresson
8’. T2 predominately orange, lacking black hairs medially;
integument of hind leg basitarsus and tibia concolorous.....9
9(8’). T5 with yellow hairs on the lateral margins; hairs long and
uneven; coxae with predominately black
hairs. . .. . .. . .. . .. . .. . .. . ... . .. . .. . .. . . .Bombus sylvicola Kirby
9’. T5 black; hairs short and even; coxae often with yellow hairs
. . . . . .. . . . . .. . . . . . . . .. . .. . .. . .. . .. . .. . ..Bombus ternarius Say
10(3’). Malar space longer than wide (though sometimes only
slightly longer than wide and appearing square)...............11
10’. Malar space as long as or shorter than wide. . .. . .. . .. . ... . . 25
11(10). Face with pale white or yellow hairs, sometimes with black
hairs intermixed, giving cloudy appearance......................12
11’. Face with predominantly black hairs............................... .16
12(11). T3 and T4 black ........................ Bombus flavifrons Cresson
12’. T3 and T4 orange or yellow or brownish. . . . . .. . ... . . . . ...13
13(12’).T3 and T4 orange. . .. . . . . . ..............................................14
13’. T3 and T4 yellow or brownish. . ... . . ...............................15
14(13). Anterior scutum with black and yellow hairs intermixed,
giving cloudy appearance . . .. . ...Bombus flavifrons Cresson
14’. Anterior scutum with predominantly yellow hairs. . .
. . .. . .. . .. . .. . .. . .. . .. . .. . . . . .. . . . . .Bombus centralis Cresson
15(13’). T5 yellow or brownish. . . . . ... . ..Bombus appositus Cresson
15’. T5 usually mostly black... . .. . .. . .. . . Bombus borealis Kirby
16(11’). T5 and T6 with orange or pale orange hairs. . . . . .. . . . . .. . .
. . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . .Bombus kirbiellus Curtis
16’. T5 and T6 with black hairs .............................................17
17(16’). T3 with mostly black hairs..............................................18
17’. T3 with yellow hairs at least medially .............................21
18(17). T4 black ........................................................................ .19
18’. T4 yellow ................................ .Bombus californicus Smith
19(18). T2 with yellow hairs medially and black hairs laterally (yel-
low often in the shape of a “W”)
. . .. . .. . ... . .. . .. . .. . .. . .. . .. . ....Bombus bimaculatus Cresson
19’. T2 yellow .......................................................................20
20(19’). Sides of the thorax with yellow hairs predominating. . .. . .
. . .. . .. . . . . .. . .. . .. . .. . .. . .. . .. . . . . . . . ..Bombus vagans Smith
20’. Sides of the thorax usually with black hairs predominating
. . .. . .. . . ..... . .Bombus perplexus Cresson (possibly in MT)
21(17’). Interalar band completely or predominantly black ..........22
21’. Interalar band predominantly yellow, if black hairs are pre-
sent they form a small circle medially. . . . . .. . . . . .. . . . . .. . .
. . .. . . . . .. . . . . .. . . .. . .. . . .. . ... . .Bombus nevadensis Cresson
22(21). T4 black .........................................................................23
22’. T4 yellow...................................................................... .24
23(22). T1 usually with yellow hairs; surface of clypeus with many
pits and punctures..... . . . . .Bombus pensylvanicus (DeGeer)
23’. T1 with black hairs, at least medially, sometimes with yel-
low hairs intermixed; surface of clypeus smooth and
shiny. . . . . .. . .. . .. . .. . .. . .. . .Bombus auricomus (Robertson)
24(22’). T2 yellow. . .. . . . . .. . . . . .. . . . . .. . .. . . ....Bombus fervidus (F.)
24’. T2 with yellow hairs medially and black hairs
laterally. . .. . .. . .. . .. . .. . .. . .........Bombus californicus Smith
25(10’). Malar space shorter than wide. . . . . .. . . . . .. . ... . ..............26
25’. Malar space as long as or slightly longer than wide. . . . . .31
26(25). Interalar band completely or predominantly black............ . .
. . .. . ................................................................................27
26’. Interalar band predominantly yellow; if black hairs are pre-
sent they form a small circle medially..............................30
27(26). T1 yellow ...............................Bombus rufocinctus Cresson
27’. T1 black.........................................................................28
28(27’). T2 yellow .......................................................................29
28’. T2 with black hairs or, if some yellow, along posterior mar-
gin only ..................................Bombus occidentalis Greene
29(28). T3 black...............Bombus cryptarum (F.) (possibly in MT)
29’. T3 yellow........................................Bombus terricola Kirby
30(26). T3 yellow, at least medially.. . ... . ... . ... . ... . ... . ... . ..
. . ... . ... . ... . ...Bombus morrisoni Cresson (possibly in MT)
30’. T3 black ............................... Bombus griseocollis (DeGeer)
31(25’). Scutellum with yellow or pale yellow hairs divided by a line
or triangle of black hairs .............. Bombus bifarius Cresson
31’. Scutellum not as above (with yellow hairs only, or yellow
and black hairs intermixed throughout)...........................32
32(31’).T2-6 black. . . . . . . . . . . . . . . . . . . . . .. . .. . . .. . . . . . . . . .Bombus
impatiens Cresson (nonnative species introduced in MT)
32’. T2-6 with some yellow and/or orange . . .. . ... . . ...............33
33(32’). Anterior scutum with black and yellow hairs intermixed,
giving cloudy appearance................................................34
33’. Anterior scutum with yellow hairs only. . . . . .. . . . . .. . . . . .. . .
. . .. . . . . .. . .. . .. . .. . .. . .. . .. . .. . .. . . . . ..Bombus frigidus Smith
34(33). Scutellum distinctly darker (with many black hairs inter-
mixed with yellow) than anterior scutum. . . . . .. . . . . .. . .
. . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .Bombus sitkensis Nylander
34’. Scutellum and anterior scutum not as above (either with scu-
tellum and anterior scutum similar in appearance, or with
the scutellum appearing lighter than the anterior scutum) . . .
. . .. . . . . .. . .. . . . . .. . . . . .. . ... . ..........Bombus mixtus Cresson
35(2’). Occiput with predominantly black hairs; hairs of face pre-
dominantly black around bases of antennae; S6 with strong
lateral ridges ...................................................................37
35’. Occiput with predominantly yellow hairs; other characters
variable...........................................................................36
36(35’). Hairs of face predominantly black around bases of anten-
nae; lateral ridges not apparent on S6 (there may be small
bumps); T6 often tightly curled under the abdomen. . .
. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....Bombus flavidus Eversmann
36’. Hairs of face predominantly yellow around bases of anten-
nae; S6 with evenly rounded lateral ridges. . .. . .
. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . ....Bombus insularis (Smith)
37(35). Hairs on the side of the thorax predominantly yellow; T4
yellow but with a triangle of black hair medially; S6 lateral
ridges extending laterad beyond T6. . .. . .. . .. . .. . .. . .. . .. . .. . .
. . .. . .. . .. . .. . .. . . ............................Bombus suckleyi Greene
37’. Hairs on the side of the thorax predominantly black; T4
yellowish-white to white, at least medially; S6 lateral ridges
barely extending laterad beyond T6 . . . . . .. . . . . .. . . . . .. . .
. . .. . . . . .. . . . . .. . ..Bombus bohemicus Seidl (possibly in MT)
Acknowledgments
This project would not have been possible without the help and support of a
large number of people. Frank Etzler, Paloma Amaral, Charles Hart, Donna
Ivie, Ian Foley, and Lauren Kerzicnik traveled many miles all over Montana
during the summer of 2015 to help collect bumble bees and/or put up insect
traps. Frank Etzler also hand-carried a bumble bee loan from Yale University
to Montana. Paloma Amaral, Joe Wood, Dayane Andrade dos Reis, Alyssa
Piccolomini, Lisa Seelye, Elizabeth Reese, Justin Runyon, Adrian Massey,
Frank Etzler, Charles Hart, Donna Ivie, and Tyler Kelly helped process speci-
mens. Lauren Kerzicnik forwarded a request for bumble bee collecting volun-
teers to the Extension Agents and Master Gardeners across the state, and
served as the recipient of those specimens in the MSU Schutter Diagnostic
Lab. Volunteers that sent in specimens included Patti Armbrister, Cynthia
Mernin, Misty Miles, Sean Foley, Kevin Foley, Katie Foley, Kari Lewis, Janet
Hamill, and Patti Fulton. Tabitha Graves and Joseph Giersch contributed
specimens collected at their USGS project sites in Glacier National Park.
James Beck created all maps in this work and designed and manages the
MTEC website and the MTEC XBio:D database. Tyler Kelly, Elizabeth
Reese, and Lisa Seelye tested the key and offered valuable feedback. Norman
Johnson, Joe Cora, and Sara Hemley at The Ohio State University offered a
great deal of assistance throughout the process of databasing all the records.
James Strange, Jonathan Koch, and Robbin Thorp verified troublesome iden-
tifications and answered morphological or diagnostic questions. Robert K.D.
Peterson, Christopher Brown, and Tyler Kelly contributed photographs to the
website. Catherine L. Delphia created Figure 6. Many thanks to Paul
Williams, Robbin Thorp, and two anonymous reviewers for offering valuable
feedback on an earlier version of the manuscript.
We would like to thank the following individuals, collection managers, cu-
rators, and database managers for their contributions to the over 12,000
Bombus records from Montana. Brian Thompson, Hayes Goosey, and Ruth
O’Neill contributed specimens from various 2015 research projects at MSU.
Ian Foley, from the Montana Department of Agriculture, contributed speci-
mens collected in CAPS project traps. Bethanne Bruninga-Socolar, from
Rutgers University, New Brunswick, NJ, contributed records from her Ph.D.
project in Montana. Leif Richardson, Harold Ikerd, Lawrence Gall, and John
Ascher contributed lists of Montana Bombus from their databases. Jessamyn
Manson, Monica Kohler, and Ashton Sturm, University of Alberta,
Edmonton, shared records and observations about bumble bees in Alberta.
The following individuals and institutions loaned specimens or hosted a visit
to examine specimens: Jason Weintraub, Greg Cowper, and Jon Gelhaus,
Academy of Natural Sciences, Philadelphia, PA; Luciana Musetti, C. A.
Triplehorn Insect Collection, The Ohio State University, Columbus, OH;
Catherine E. Siebert, Bozeman, MT; Christopher Grinter, Illinois Natural
History Survey, Champaign, IL; the Laura Burkle Lab (which includes E.
Reese, M. Simanonok, L. Heil, and S. Adhikari) at MSU; Jen Marangelo,
Missoula Butterfly House and Insectarium; John Swann, Museum of
Zoology, University of Calgary, Alberta; Brian Harris, Sean Brady, and Floyd
Shockley, National Museum of Natural History, Washington, D. C.; Leonard
Munstermann and Lawrence Gall, Peabody Museum of Natural History,
Yale University, New Haven, CT; Jennifer Thomas and Zachary Falin, Snow
Entomological Museum, University of Kansas, Lawrence; Virginia Scott,
University of Colorado Museum of Natural History, Boulder, CO.
The Montana Department of Agriculture’s (MDA) Specialty Crop Block
Grant Program provided support for the portion of this project involving pol-
linators of huckleberries via a grant to M.A.I. Survey work in eastern
Montana during 2015 was supported by MDA and USDA-APHIS contracts
to M.A.I. for invasive species detection. Bumble bee specimens collected as
part of a Western Sustainable Agriculture Research and Education (WSARE)
grant (SW13-043) were included in this work. This is a contribution of the
Montana Agricultural Experiment Station.
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