85 Worker resource storage as an overwintering strategy in the western thatch ant, Formica obscuripes

Faculty Mentor: John Longino (Biological Sciences, University of Utah)

In highly seasonal temperate habitats insects exhibit overwintering strategies. Perennial ant colonies must overwinter as a functional colony. Formica obscuripes is a common ant in western North America that builds conspicuous thatch mounds and can be an ecologically dominant species in mountain habitats. In the winter, the colony descends to more than a meter deep, and it is known that they overwinter as the queen(s) and adult workers only, with no immatures (eggs, larvae, pupae). Yet in early Spring they seem to begin reproduction almost immediately. We hypothesized that workers were storing resources in their bodies, as fat or other storage compounds, which could be mobilized in early Spring to begin feeding larvae. These resource dynamics would be reflected in winter workers hav ing greater size-adjusted dry weight thansummer-active workers. On average, summer foragers collected on the nest were 50% lighter than winter workers. Further research should track colony phenology at greater temporal resolution, to see if larvae begin to grow and workers lose weight prior to foraging in the Spring, and the nature of weight gain in the Fall.