The rusty patched bumble bee (Bombus affinis) is named after the small rust-colored patch visible on worker bees' abdomens. Worker bees also have yellow on the first and rear half of the second abdominal segment. The remaining abdominal segments are black. Queens and males resemble workers except that they lack the rust-colored patch. Queens are larger in size than workers and have a small central bare patch on the thorax.

This bee was historically found throughout the eastern and upper midwestern United States. However, surveys between 2003 and the present have found only a small number of this species in Illinois and Wisconsin.