Forest Preserve District of Cook County, Illinois
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Mosquito Life Histories
Nature Bulletin No. 682   June 2, 1962
Forest Preserve District of Cook County
John J. Duffy, President
David H. Thompson, Senior Naturalist

Everybody knows that a mosquito is a small, long-legged insect that bites. However, there are many kinds of them each with its own peculiarities of life history and habits. Some are produced in marshes or in flood plains of streams, some in puddles, some in woodlands, and others in cities and towns. Here in the Chicago region, although mosquito-borne diseases are no longer a danger, they become nuisances in many places at certain times in almost every year. In times past and in many countries the mosquitoes which carried malaria, yellow fever and other infections shaped the course of history. Hundreds of scientists have studied them for years but much remains to be learned.

All mosquitoes pass through four distinct stages in their life history -- egg, larva, pupa and the flying adult. The mosquito larva is commonly called a wiggletail, wiggler or wriggler; and the pupa a tumbler.

The eggs of mosquitoes have shapes like spindles -- but so small that a single egg can scarcely be seen with the naked eye. The females of the twenty or thirty species in this region lay their eggs in one of three ways. The rather rare malaria mosquito, Anopheles, for example, lays eggs singly on weedy backwaters and pools where they hatch after a few days. The widespread house mosquito, Culex pipiens, is typical of several local species of a second type. It glues a hundred or more eggs into a tiny floating raft on the stagnant or polluted water collected in garden pool s, catch basins, clogged gutters and junk heaps. The extremely troublesome floodwater mosquitoes are a third type. They lay their eggs in damp places just above the water line of swamps and marshes. The eggs lie dormant until they are flooded by a warm rain, then hatch in a matter of hours. The eggs of our most abundant floodwater species, Aedes vexans, may produce a new generation every few weeks or hold over for two years or more, depending on summer water levels. That fierce biter, Aedes stimulans, must have its eggs frozen before they hatch.

All mosquito larvae, or wigglers, live in water -- even in tree holes, pitcher plant leaves and flowing streams. They feed on small plant and animal life, either alive or dead, which they scoop into their mouths with brushlike rakes. The larvae of one kind devours other mosquito wigglers. As they grow they shed their skins four times for new and larger ones. They breathe air at the surface either through a snorkel tube or a plate on the rear of the body. When alarmed they dive tail first to the bottom with whip-like somersaults. An exceptional species gets its oxygen by piercing the underwater air chambers of cattails and other water plants.

After a week or two as wigglers, they change into acrobatic tumblers shaped like big-headed question marks. These breathe air through a tube on the back but they do not eat. After a few days, they come to the surface, the skin pops open, the adults crawl out onto the water, the wings unfold, then they fly away.

Both sexes hum or "sing" in flight but only the females suck blood. The males feed on nothing but plant juices and nectar. The females of most species require a meal of blood before they can produce eggs but usually get it from our livestock and wild mammals. A few prefer birds' blood but one of our most common kinds never takes blood. A few bite in the shade in daytime but the worst pests are active in the evening and at night.

The entire life cycle of the mosquito can be watched in the schoolroom or laboratory by bringing in some stagnant water with an egg raft of the house mosquito, or by soaking a piece of sod from a dried-up marsh containing the eggs of floodwater mosquitoes.

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