A bumble bee in a haystack: chance observation of an overwintering rusty patched bumble bee, Bombus affinis (Hymenoptera:Apidae) gyne

Bombus affinis (rusty-patched bumble bee) Cresson is listed as a federally endangered species in the United States and Canada. It is globally “imperiled” (G2) and listed as “critically endangered” on the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. While the causes of the species’ precipitous decline are relatively unknown, researchers suspect introduced pathogens, habitat loss and degradation, competition with non-native bees, and climate change. Conservation strategies should encompass all aspects of the species’ life cycle. However, habitat selection of new overwintering gynes (gynes become queens when they establish nests in the spring) is the least understood. Here we document the first observation of an overwintering B. affinis gyne in an urban deciduous forest in Madison, Wisconsin. The gyne was discovered on a slight north, northeast facing slope within the top 5 cm of loose soil and under a layer of Acer saccharum, Quercus sp., and Tsuga canadensis leaf litter. We mapped the landcovers within 1 km and 2 km around the observed overwintering location as the potential foraging range that a newly emerged queen would encounter the following spring. While only a single observation, this chance encounter adds to the knowledge of overwintering habitat requirements and increases our understanding of the land cover types that B. affinis queens might encounter within the foraging range of the overwintering site, especially those within a highly urbanized landscape. Observations such as this can inform conservation and recovery efforts for the imperiled B. affinis.