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Chironomid Swarms

Male chironomid - ©Entomart.

Chironomids, named after their scientific family group Chironomidae, are commonly referred to as “non-biting midges” to distinguish them from their biting relatives (like “no-see-ums” that bite humans voraciously). They are dipteran cousins to mosquitoes (Diptera commonly known as true flies which include many familiar insects like mosquitoes, black flies, midges-both biting and non-biting, fruit flies and house flies). Very often adult chironomids are mistaken for mosquitoes by the public, because they look just like adult mosquitoes apart from the fact that they lack a “proboscis” (blood sucking organ) and reason adult chironomids do not bite.

In fact adult chironomids are highly visible in their clustered swarms when they hatch from water environments but they for the most part, do not feed during their adult flying stage. Chironomids go through the same developmental stages in their lifecycles as mosquitoes: egg, larva, pupa and adult. The major difference between them and mosquitoes are:

  1. Mosquitoes spend about a week or two in the larval stage and then emerge as biting adults (only females need a blood meal to lay eggs). These adults can then live for several months to a year and some can even over-winter and survive a second year as an adult.
  2. Chironomids spend a much longer time in the larval stage (several months). Chironomid larvae can also over-winter for a second season in the larval stage and then finally emerge as non-biting adults that only live for a week or two and then die. Swarms of adult midges emerge to find mates, quickly reproduce and then females lay their eggs on water surfaces and shortly thereafter all the adults die. Most species in the adult stages do not feed at all.

Several years of insect emergence studies and data collected on the refuge have shown that chironomids are the most dominant and numerous insect group in biomass and abundance within Prime Hook’s aquatic ecosystems. In fact more than 70% of all aquatic insect larvae that emerge into the adult stage are chironomids, whereas less than 1% of insects collected in emergent traps are mosquitoes. This dominance of chironomid larvae in refuge habitats provide very important food resources for fish, amphibians, aquatic invertebrates, waterfowl, shorebirds and other migratory birds.

Adult chironomids also provide food for bats, amphibians and other insect-feeding birds. During any given year the refuge, will experience several large scale adult chironomid swarms. Multiple adult emergence events occur when ideal weather conditions (warmer water and air temperatures and extensive areas with “stable water levels”) prevail.

Optimal climatic factors provide great environmental conditions for high densities of chironomid larval and adult populations. Normally, these adult swarms on and near the refuge will materialize beginning in late May-early June, with a second emergence in late July and a possible third large emergence event in late September. The number of emergence events or swarms per year is strictly weather dependent. This year a wet summer, warm fall temperatures and additional heavy rainfall from a “Government Shutdown Nor’easter” have resulted in a fourth swarm that emerged in late October.

Adult chironomids are very attracted to outdoor lights in the evening and/or to white colored siding of buildings where they tend to gather and accumulate in large swarms. Soon most of them die and homeowners near aquatic habitats can easily wash or sweep away remnant adults when they die after they have performed their annual reproductive chores. Eggs deposited on the water surface after each swarming event will soon develop into larvae that will eventually emerge next spring when climatic factors are favorable again.

Page Photo Credits — Male chironomid - ©Entomart.
Last Updated: Nov 27, 2013
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