The rusty-patched bumble bee (Bombus affinis) was once commonly found across the northern part of eastern North America, extending south along the Appalachian mountains. It is now listed as an endangered species in the US and Canada, currently found in low numbers in a very small part of its former range. Scientists and conservationists need your help finding the remaining populations of this bee. Please take photos and share on www.bumblebeewatch.org Read below to learn how to distinguish the rusty-patched bumble bee from other bumble bees.
There are two key features to look for to distinguish the rusty-patched bumble bee males and workers from other bumble bees.
- The rusty-patch: The eponymous rusty-patch is a bit subtle. It varies greatly in color, from brown to orange. The patch appears on the 2ndsegment of the abdomen. The hairs on the 1st segment are yellow, the 2nd segment is mostly yellow, but with a central patch of rusty-brown-orange hair at the front edge of the segment, going about half way back. The rear edge of the second segment has entirely yellow hair. The 3rdand all proceeding segments of the abdomen are covered with black hair.
- The thumb-tack: The hairs on the thorax of the rusty-patched bumble bees are yellow with a T-shaped area of black hairs with the top part of the T stretching between the wings with a thin line extending down the middle towards the back of the thorax. They are not the only bumble bee with this coloring on the thorax, but if you think you see the rusty-patch on a bee, make sure you can also see the thumb-tack.
The species most commonly confused with rusty-patched are the tri-colored, the brown-belted, the half-black, and the red-belted.
The tri-colored (Bombus ternarius) has bright orange hairs on segments 2 and 3 of the abdomen.
The brown-belted (Bombus griseocollis) has a rusty brown patch on the second abdominal segment, but it is bordered at the back by black hairs. They also do not have the thumb tack of black hairs on their thorax.
The half-black (Bombus vagans) can appear to have a patch on the second abdominal segment, but this is trick of lighting and is usually just a spot that appears darker due to the dark cuticle showing through a thinner patch of hair. They also do not have the thumb tack of black hairs on their thorax.
The red-belted (Bombus rufocinctus) has many different color patterns. Some have orange hairs on the 2nd abdominal segment, but they also do not have the thumb tack of black hairs on their thorax.
The rusty-patched bumble bee is unique among the bumble bees of North America in that the queens have a different color pattern than the workers. Queens are usually only seen in the spring and the fall. Despite their name, the queens do not have a rusty patch. They also do not have the black thumb-tack on their thorax. Abdominal segments 1 and 2 are entirely yellow. Their key features are a bit more difficult to distinguish from the similarly colored half-black bumble bee.
- Short face: The face of all rusty-patched bumble bees is short and round. Compare this to the long face of the half-black bumble bee, which has a similar color pattern on the abdomen.
- Black hair on top of head: The half-black bumble bee has mostly yellow hair on the top of the head, whereas the rusty-patched bumble bee has mostly black hair on top of the head.
- Cropped hair: The hair on the thorax of the half-black bumble bee is longer and messier looking than the hair on the thorax of the rusty-patched bumble bee queens.
- Size: While size is highly variable within most bumble bee species, the rusty-patched bumble bee is generally larger, and stouter than the half-black bumble bee.