Flies

Flies are well adapted for aerial movement, and typically have short and/or streamlined bodies. The second segment of the thorax, which bears the wings and contains the flight muscles, is greatly enlarged, with the other two segments being reduced to mere collar-like structures. The third segment bears the halteres, which help to balance the insect during flight. A further adaptation for flight is the reduction in number of the neural ganglia, and concentration of nerve tissue in the thorax, a feature that is most extreme in the highly dervied Muscomorpha infraorder.

Flies have a mobile head with eyes, and, in most cases, have large compound eyes on the sides of the head, with three small ocelli on the top. The antennae take a variety of forms, but are often short, to reduce drag while flying.

Flies consume only liquid food, and their mouthparts and digestive tract show various modifications for this diet. The most apparently primitive flies have piercing blade-like mandibles and fleshy palps, but these have become adapted into numerous different forms in different groups. These include both the fine stilleto-like sucking mouthparts of mosquitos, and the fleshy proboscis of houseflies. The gut typically includes large diverticulae, allowing the insect to store large quantities of liquid after a meal.