Rusty Patched Bumble Bee | Xerces Society (2024)

Connecticut

Delaware

Georgia

Illinois

Indiana

Iowa

Kentucky

Maine

Maryland

Massachusetts

Michigan

Minnesota

New Hampshire

New Jersey

New York

North Carolina

North Dakota

Ohio

Pennsylvania

South Carolina

South Dakota

Tennessee

Vermont

Virginia

West Virginia

Wisconsin

Ontario

Quebec

The rusty patched bumble bee is a species of bumble bee native toeastern North America. Itsworkers and males have a small rust-colored patch on the middle of their second abdominal segment. This bee was once commonly distributed throughout the east and upper Midwest of the United States, but has declined from an estimated 87% of its historic range in recent years. The rusty-patched bumble bee was once an excellent pollinator of wildflowers, cranberries, and other important crops, including plum, apple, alfalfa and onion seed.

Responding to apetitionfiled by the Xerces Society in 2013 to list the rusty patched bumble bee as an endangered species under the US Endangered Species Act (ESA), the U.S. Fish and Wildlife Service (USFWS) finalized the ruling and gavethe rusty patched bumble bee endangered status under the ESA in January of 2017.

In order to properly identify any bumble bee, you need to firstdetermine whether the bee you are examining is a female worker, a queen or a male bee. Then, you can begin to determine whether your bee is a Rusty-patched Bumble Bee or some other species of bumble bee. The rusty-patched bumble bee workers have a distinctive rusty patch on the front half of their second abdominal segment. The first abdominal segment and the rear half of their second abdominal segment are both yellow. All other abdominal segments are black. The hair on the heads ofB. affinisworkers is mostly black throughout. On the thorax, black hairs extend from a central patch in the middle of the thorax out towards the wings and centrally in a narrow V towards the rear. The coloration ofBombus affinisqueens and males differ from the workers in their lack of a strong rusty patch on the second abdominal segment. Queens also differ in having the thorax mostly yellow except for a small central bare patch. Similar bumble bees that occur in the same region areB. vagans,B. griseocollis,B. impatiens,andB. bimaculatus.

DistinguishingB. affinisfromB. vagans

Bombus affinis (left) and Bombus vagans (right)

B. vaganshave a longer face thanB.affinis.B. vagansworkers and queens have yellow hair on the first two abdominal segments and black on the rest of the abdominal segments. There is no rusty patch on their abdomen.B. vaganshave a patch of yellow hair the top of their heads in contrast withB. affinispatch of black hairs.

In addition to the lack of the rusty patch, maleB. vaganscan be distinguished fromB. affinisby yellow hairs along the margins of their abdominal segments and some yellow hairs mixed in among the black hair of the more apical abdominal segments.

DistinguishingB. affinisfromB. griseocollis

Bombus affinis (left) and Bombus griseocollis (right)

Bombus griseocolliscan be distinguished fromB. affinisby several key features.B. affinishave a stripe of black hairs that extends between the wings on the thorax.B. griseocollishave a central bare black spot with only a few black hairs at the edges of this spot. The hair on the thorax ofB. griseocollisworkers is predominately yellow.B. affinishave yellow hairs extending to the lateral margins of the second abdominal segment.B. griseocollishave black hairs along the sides of the second abdominal segment.B. griseocollisdoes have a rusty brownish patch in the middle of its second abdominal segment but this patch is flanked by black hairs along the rear and the sides of the segment.

MaleB. griseocollisare easily distinguished fromB. affinisby their large eyes and a prominent patch of dense yellow hairs on the front of their faces.

DistinguishingB. affinisfromB. impatiens

Bombus affinis (left) and Bombus impatiens (right)

B. impatiensqueens, workers, and males have yellow on only the first abdominal segment, with the rest of the segments black, whereasB. affinishave yellow on the first and second abdominal segments. Also,B. impatienshave a bare patch in the middle of the thorax surrounded by yellow hair, as opposed toB. affiniswith their patch of black hair extending between the wing bases. MaleB. impatienshave a prominent patch of yellow hair on the front of their face, as opposed toB. affiniswith mostly black hair on the front of the face.

DistinguishingB. affinisfromB. bimaculatus

Bombus affinis (left) and Bombus bimaculatus (right)

B. bimaculatushave longer faces thanB. affinis.B. bimaculatusqueens, males, and workers have black along the sides of their second abdominal segment, whereasB. affinishave yellow hairs that extend to the sides. B. bimaculatushave yellow hairs in a central notched pattern on the second abdominal segment. Workers ofB. bimaculatusalso have a bare patch in the middle of the thorax surrounded by predominately yellow hair, as opposed toB. affiniswith their patch of predominately black hair extending between the wing bases. MaleB. bimaculatushave a prominent patch of yellow hair on the front of their face, as opposed toB. affiniswith mostly black hair on the front of the face.

For an online key, photographs of specimens of the rusty-patched bumble bee and extensive identification information, visit its’ Bumble Bee Watchspecies profile pageor, theDiscover Lifewebsite.

All bumble bees belong to the genusBombuswithin the family Apidae. The family Apidae includes the well-known honey bees and bumble bees, as well as carpenter bees, cuckoo bees, digger bees, stingless bees, and orchid bees.B. affinisbelongs to a sub-genus ofBombus,Bombus sensu stricto.

Bumble bees are important pollinators of wild flowering plants and crops. As generalist foragers, they do not depend on any one flower type. However, some plants do rely on bumble bees to achieve pollination. Loss of bumble bees can have far ranging ecological impacts due to their role as pollinators. In Britain and the Netherlands, where multiple bumble bee and other bee species have gone extinct, there is evidence of decline in the abundances of insect pollinated plants.

Bumble bees are also excellent pollinators of many crops. Bumble bees are able to fly in cooler temperatures and lower light levels than many other bees, and they perform a behavior called “buzz pollination”,in which the bee grabs the pollen producing structure of the flower in her jaws and vibrates her wing musculature causing vibrations that dislodge pollen that would have otherwise remained trapped in the flower’s anthers. Some plants, including tomatoes, peppers, and cranberries, require buzz pollination.

Historically, the rusty-patched bumble bee was distributed along the east coast of the United States from southern Maine south through Georgia with an extension west along the northern states through Minnesota. A few individuals have been found as far west as North Dakota. The former range of the Rusty-patched bumble bee includes these states: Minnesota, Wisconsin, Indiana, lower Michigan, Ohio, Pennsylvania, New York, Vermont, New Hampshire, Maine, Maryland, Virginia, North Carolina, South Carolina, Georgia, Connecticut, Massachusetts, Delaware, New Jersey, West Virginia, and portions of North Dakota, South Dakota, Iowa, Illinois, Kentucky, and Tennessee. A number of surveys have been done, but the Rusty-Patch Bumble Bee has not been found in most of its range since 2003 with the exception of a few isolated areas.

Although this species was formerly commonly found through most of its range, surveys between 2003 and present have found very fewB. affinis. Recently,B. affinishas been found in small numbers in isolated areas primarily in the northern part of its range. In 2017 this species was listed asendangered under the U.S. Endangered Species Act. In 2014 the state of Vermont listedB.affinisas an endangerd species and in 2015 this species was listed asCritically Endangered on the IUCN Red List. In CanadaB. affiniswas protected under the federalSpecies at Risk Act(SARA) in 2010.

There are a number of threats facing bumble bees, any of which may be leading to the decline of the rusty-patched bumble bee. The major threats to bumble bees include: spread of pests and diseases by the commercial bumble bee industry, other pests and diseases, habitat destruction or alteration, pesticides, invasive species, natural pest or predator population cycles, and climate change.

Commercial bumble bee rearing may be the greatest threat toBombus affinis.In North America, two bumble bee species have been commercially reared for pollination of greenhouse tomatoes and other crops:B. occidentalisandB. impatiens. Between 1992 and 1994, queens ofB. occidentalisandB. impatienswere shipped to European rearing facilities, where colonies were produced then shipped back to the U.S. for commercial pollination. Bumble bee expert Robbin Thorp has hypothesized that these bumble bee colonies acquired a disease (probably a virulent strain of the microsporidianNosema bombi) from a European bee that was in the same rearing facility, the Buff-tailed Bumble Bee (Bombus terrestris). Dr. Thorp hypothesized that the disease then spread to wild populations ofB. occidentalisandB. frankliniin the West (from exposure to infected populations of commercially rearedB. occidentalis), andB. affinisandB. terricolain the East (from exposure to commercially rearedB. impatiens). In the late 1990’s, biologists began to notice thatB. affinis, B. occidentalis, B. terricola,andB. frankliniwere severely declining.

Many parts of this hypothesis weresupported byrecent scientific evidencewhich documented thatcommercial bumble bees were responsible for the spread and amplification ofNosema bombi,and that this likely has had a profound effect on wild bumble bees, including the rusty patched bumble bee. They did not find evidence that the pathogen had been introduced from Europe. Bumble bees are reared commercially for use as pollinators of agricultural crops and it has been clearly documented that these commercial bumble beescarry high pathogen loads, and regularly interact with wild bumble bees near greenhouses and in open field settings.

Besides the threat posed by the commercial bumble bee industry, there are many other threats to wild bumble bee populations. Bumble bees are threatened by many kinds of habitat alterations which may destroy, alter, fragment, degrade or reduce their food supply (flowers that produce the nectar and pollen they require), nest sites (e.g. abandoned rodent burrows and bird nests), and hibernation sites for over-wintering queens. Major threats that alter landscapes and habitat required by bumble bees include agricultural and urban development. Livestock grazing also may pose a threat to bumble bees, as animals remove flowering food sources, alter the vegetation community, and likely disturb nest sites. As bumble bee habitats become increasingly fragmented, the size of each population diminishes and inbreeding becomes more prevalent. Inbred populations of bumble bees show decreased genetic diversity and increased risk of decline.

Insecticide applications on farms poses a direct threat to foraging bumble bees. Specifically,theuse of highly toxic insecticides known as neonicotinoids continues to grow throughout the range of the rusty patched bumble bee.A number of scientific articlesclearly document the lethal and sublethal effects that these chemicals are having on bees and other pollinators, and their use has intensified extensively within the rusty patched bumble bee’s range during the same time period that declines have been observed. Moreover, the massive increase in the past two decades in the use of the herbicide glyphosate on genetically modified corn and soybean fields has beeneffective at eliminating milkweed from the agricultural landscape. It is likely that other wildflowers have also been eliminated from farm edges – and it is reasonable to assume that a major loss of floral resources from the Upper Midwest could have had an effect on the rusty patched bumble bee. While no direct link has been made from the use of these pesticides to the declines observed in the rusty patched bumble bee there is little doubt that stressors like pesticides at the very least put increased pressures on an already imperiled bumble bee, especially when one considers the scope at which these chemicals are being adopted and used.

Bumble bees are threatened by invasive plants and insects. The invasion and dominance of native grasslands by exotic plants may threaten bumble bees by directly competing with the native nectar and pollen plants that they rely upon. In the absence of fire, native conifers encroach upon many meadows, which removes habitat available to bumble bees. The small hive beetle (Aethina tumida) is an invasive parasite of the honeybee, yet it also infests bumble bee colonies. Its actual impact on bumble bee colonies could be severe, although it has not been well studied.Global climate change also poses a real threat to bumble bees; anecdotal evidence has suggested that some of the bumble bee species adapted to cool temperatures are in decline, whereas warmer adapted species are expanding their ranges. Baseline data and long term monitoring are needed to better understand the true impact of climate change on bumble bees.

Much of the content for this page was developed from a status review, co-authored by professor emeritusRobbin Thorp(U.C. Davis Department of Entomology), Elaine Evans, Sarina Jepsen and Scott Hoffman Black (Xerces). Bee illustrations were provided by Elaine Evans.

Funding for our efforts to conserve bumble bees in decline has been generously provided by the CS Fund and Xerces Society members.