- insects with wings, or insects whose ancestors had wings
Immature mayflies are aquatic and have abdominal gills, two cerci, a median filament and chewing mouth parts. The terrestrial (living out of water, on the land) adults, however, have vestigial mouth parts and do not feed. The pale brown coloured mature adults live only one or two days, and their main purpose is to find a mate, reproduce and continue the species. Adults vary from 4 to 50 mm in body length and have two long filament-like cerci extending from the tip of the abdomen. Mayflies normally have two pairs of membranous wings with a lacy network of many longitudinal and cross veins that are held upright over the body when at rest. Unlike other insects mayflies have a winged stage, called subimago preceding the adult stage (imago). This stage is similar to the adult in all ways except that it cannot fly and is sexually immature. The subimago is a brief stage and moults into the fully mature adult. Adult mayflies often emerge in large numbers from lakes, streams and ponds, and they are especially attracted to night lights. Their populations are reduced in polluted waters, hence they are good indicators of clean water. Species of the genus Hexagenia are common residents of northwestern Ontario.
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