The muscid flies have a range of larval forms depending on the species. Some are simple maggot-like forms lacking any conspicuous structures (prolegs, welts, siphons etc). One muscid group resembles the genus Limnophora (known overseas) and is larger than other muscids, with obvious prolegs and 2 respiratory siphons. The larvae of all forms have no obvious head structure.
Muscid larvae are found in many stream types, and they can be particularly common amongst algal mats on stony streambeds.
Muscid larvae are thought to be predators, probably feeding on other fly larvae and worms.
Muscids can be found in good quality streams, but they can also thrive in quite polluted streams. Their ability to live in polluted habitats explains their low tolerance values of 3 (hard bottom sites) and 1.6 (soft bottom sites).