Overwintering behaviour of the skipper fly (Diptera: Piophilidae) of forensic importance in Québec, Canada

Laboratory experiments and field observations from August 2019 to April 2020 demonstrated that skipper flies (Diptera: Piophilidae) overwinter as larvae and likely present an obligatory winter diapause in Québec, Canada. Diapause was confirmed by the very few emergences of adults in the laboratory following collection from carrion at the end of summer and in fall, the migration of larvae deep in the soil, and the persistence of larvae inside carrion during the winter until the following spring when they became active again and initiated pupation (i.e., intra-puparial period). To our knowledge, our observations represent the first report of the overwintering of skipper fly larvae inside an animal carcass in North America. In addition, this winter diapause should be considered in forensic entomology when using the presence of skipper fly larvae on a body to estimate the time elapsed since death.