The integument of the house fly larva consists of an outer acellular cuticle and an inner single layer of epithelium which rests on a basement membrane. The cuticle is covered with an epicuticle and has a stratified structure. The cuticle is 5µm thick in young larvae (36 hours old), 25µm in 60-hour-old larvae and 40µm in last (third) instar larvae.
The larva is white and cylindrical, with the posterior end broad and flattened. It tapers anteriorly.
There are no eyes or appendages, although there are some ventral spiny ridges which aid locomotion. The larvae have 13 segments, but the first two are partially fused so that only 12 segments are apparent.
Some of the internal organs may be seen through the cuticle. The spiracles are openings for air to enter the respiratory system of the larva. The posterior spiracles (on the broad blunt end) are distinctive.
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