Midges below zero: A review of hibernal emergence of Chironomidae in temperate regions

Abstract

The Chironomidae are one of several groups of aquatic insects with representatives that possess cold hardening strategies that allow pronounced hibernal activity, including species that complete their life and reproduce only during the coldest months of the year. Although these winter-active species are often ignored in aquatic studies, relatively recent research has demonstrated that these insects are not only interesting, but they can also be an important and diverse element of aquatic insect communities. This review synthesizes existing literature on winter-emerging Chironomidae, focusing largely on Holarctic species emerging from temperate streams that are at least partially ice-free throughout the winter season. We found that there are currently at least 215 chironomid taxa present during winter, predominated by Orthocladiinae (n = 127), Chironominae (n = 42) and Diamesinae (n = 35). Our review highlights cold hardening strategies, such as supercooling, that permit winter activity, and we also discuss growth and emergence for species that have been extensively studied, such as Diamesa mendotae Muttkowski. Winter-active species tend to be long-lived at cold temperatures, and we discuss how consequences of climate change, including warmer temperatures and reduced snowpack, may negatively impact certain winter-active species. Although there is a growing base of studies featuring winter-active species, our review demonstrates that research is largely restricted to a handful of localities, and autecology studies are limited to only select species. We emphasize the importance of extending field work into the winter season and expanding research on winter Chironomidae to a broader geographic range to better gauge species accounts and enhance our understanding of the importance of winter-emerging Chironomidae.