The bottom fauna will be reduced or absent in lakes where the deep water looses oxygen for the duration of summer stagnation, or in winter. A mesotrophic system with a stable thermocline in the summer months looses most of its oxygen for a time during stagnation but not for the entire period. Larvae pass through 4 instars before pupating. The pupal stage lasts no more than a few days. The mouthparts are generally reduced, as few adults live for more than a few days.
Adults often emerge, simultaneously, in huge numbers, and proceed to form vast mating clouds.
They are especially attracted to lights. In temperate regions, many chironomid species are uni- or bivoltine, but up to four generations in a year are not uncommon. Species living in the cold, profundal zones of deep lakes may take more than one year to complete their life cycles, and circumpolar species require at least two years, and occasionally, as many as seven. In such long-lived species, the larvae coil up in cocoons and overwinter under freezing conditions. In highly transient, tropical habitats such as rainpools, life cycles may be as short as a few weeks.