Housefly

They are the prey of many animals.

An excerpt from the article 22 facts about Housefly
They constitute a significant meal for birds, reptiles, amphibians, spiders, and other insects. In turn, eggs, larvae, and pupae are usually threatened by parasitism.

Histeridae beetles feed on fly larvae and some mites larvae such as  Macrocheles muscaedomesticae feed on fly eggs. A single larva is capable of eating 20 of these per day.