Two-spotted Bumble Bee

Appearance

"Bombus bimaculatus" was first described by Ezra Townsend Cresson, an American entomologist, in 1863.

Workers look very similar to queens, with the two mainly distinguished by size. Sometimes large workers can be mistaken for small queens, especially toward the end of the season when workers have grown larger and new queens emerge. Queens have a black face with a triangular patch of yellow hairs on the vertex. Their thorax is yellow except for a shining area on the disc that is bordered by black hairs. Their venter is black with some yellow hairs on the legs.

Male faces have intermixed black and yellow hairs. They resemble females in most markings, except their tergite 2 has more yellow lateral hairs than the female whose tergite 2 has black edges and few yellow lateral hairs.

The size of the radial cell in the wing differs for each. Workers have the smallest, ranging from 2.5 to 3.6 mm. Males are slightly bigger at 2.6–3.6 mm. Queens have the largest at 3.4–4.1 mm.

Naming

The bee's common name comes from the two yellow spots on its abdomen.

Distribution

"B. bimaculatus" is mainly found in eastern temperate forest regions throughout the United States and the southeastern part of Canada. It can also live in the coastal plains of the southeastern United States, the eastern Boreal forest, and the eastern Great Plains.

This bee lives in underground nests, preferably in or around wooden areas and gardens. Nests can be anywhere from 6 inches to a foot below the surface. Tunnels traveling to the nest range from 9 inches to 4 feet long. "B. bimaculatus" can also nest above ground or in cavities. Bees do not build nests and instead rely on finding abandoned rodent dens, hollow logs, suitable man-made structures, or tussocks. Queens will hibernate in loose dirt or rotting logs.

This bumble bee is very common and has been experiencing steady growth unlike many other bumble bees that are in decline.

Status

Unlike many of the other species of bee in the genus "Bombus," "B. bimaculatus" is not on the decline, but instead is very stable. They are abundant pollinators that forage at a variety of plants.

Food

Bumble bees eat nectar and pollen from plants. "B. bimaculatus" is known to pollinate a wide variety of plants, but they seem to have favorites. Queens can be found on willow and plum. Workers are found on red clover and mint. Males are found on mint and sweet clover.

As a species they have been found foraging at the following plants:
⤷  "Zenobia pulverulenta"
⤷  "Gelsemium sempervirens"
⤷  "Lyonia lucida"
⤷  "Solanum dulcamara"
⤷  "Aquilegia" species
⤷  "Dicentra" species
⤷  "Mertensia" species'
⤷  "Pedicularis" species'
⤷  "Aesculus glabra"
⤷  "Camassia scilloides"
⤷  "Delphinium tricorne"
⤷  "Hydrophyllum appendiculatum"

Predators

Predators of bumble bees include crab spiders, Florida black bears, ambush bugs, robber flies, dragonflies, assassin bugs, and some wasp species. Crab spiders ambush "B. bimaculatus" at flowers, paralyze them, and then eat them. Florida black bears eat "B. bimaculatus" most abundantly in the spring, and continue to eat them to a lesser extent in the summer.

Defense

"B. bimaculatus" will defend its nests against intruders, such as "Psithyrus variabilis", a cuckoo bumble bee. In an experiment, a female "P. variabilis" was placed in a "B. bimaculatus" nest. Workers quickly recognized her as an intruder, halted their work and attacked her when she entered the inner part of the nest.

Oftentimes though, "B. bimaculatus" are content to ignore intruders, such as "Psithyrus labrosius". Like "P. variabilis," "P. labrosius" also is a cuckoo bumble bee. It will attack "Bombus vagans", but not "B. bimaculatus" though they are in the same subgenus, "Pyrobombus".

"B. bimaculatus" queens can kill each other when dueling. Queens can also be hostile to unrelated workers of their own species by squirting feces in their faces.Only female bees have a sting, males do not. Bumble bees typically only sting when defending their nest or when captured. Allergies to bumble bee stings are much less common than allergies to honey bee stings though the venom composition is similar. "B. bimaculatus" venom contains additional proteins, including acrosin and a tryptic amidase related to clotting enzymes.