Larval Stage in Water
- During the larval stage, the true flies that require water for the larval stage have larva that can crawl around. Some develop little "prolegs" (not true legs) that they use to maneuver around stream and lake beds. Other true fly larvae wriggle like worms, while yet others feature a row of six suction discs that allow them to move like caterpillars. Larvae such as mosquito larvae swim.
Larval Stage on Land
- The housefly, a true fly, has a larval stage that lives in warm sheltered areas such as manure piles and soil containing manure. Its larvae, called maggots, are legless and move by sending ripples along their body length. They move either above ground or underground up to 50 feet away from their warm moist egg location to reach a dry, cool place in order to change into pupae.
- Following the fourth molt, the fly enters the pupa stage and creates a pupa case. During the pupae stage, most of the movement is restricted to motion inside the pupal skin that enables the fly to develop into an adult. Once the pupae stage has come to an end, usually within two days, the skin splits and the adult emerges. One exception is the mosquito pupa which lives at the water's surface and dives in a tumbling, jerking motion when disturbed.
- The structures behind the wings on a true fly, where the hind wings are on other insects, look like tiny stalked knobs. These are called halteres and may aid the fly in direction and balance.
The transparent, membranous wings of true flies function like normal wings and beat typically 200-400 beats per second for smaller flies and up to 1,000 strokes per second for tiny midges.
The adult true fly also ambulates on its six jointed legs.