True Flies (Diptera)
This large order of insects, second only to beetles (Coleoptera) in diversity, is the dominant order of aquatic insects. There are about 17,000 species in North America with nearly 3,500 species being aquatic. Iowa likely has several hundred species of aquatic dipterans, with about a third of these in the family Chironomidae (midges). As a group, aquatic Diptera have been poorly studied in Iowa and most other places. Many larvae cannot be identified to species and many adults (which can be identified to species) have never been linked to their larval stages. Several groups within the order have been better studied because they are pests or potentially pose public health risks. Examples are mosquitos, black flies, deerflies and horseflies. At first glance, many aquatic diptera larvae look like maggots or worms and can be distinguished from all other aquatic insects by the lack of three pairs of legs on the thorax. Some have fleshy "leg-like" features (prolegs, pseudopods, creeping welts) but no jointed legs like a caddisfly,for example, displays. Adult Diptera have only two (di) wings (ptera) instead of the four that most other winged insects have.