In some species, the larvae are saprotrophs, specifically detritivores,[1] eating decaying plant and animal matter in the soil or in ponds and streams.

Insects such as aphids are considered crop pests, so the aphid-eating larvae of some hoverflies are economically and ecologically important.

Hoverflies are harmless to most mammals, though many species are mimics of stinging wasps and bees, a mimicry which may serve to ward off predators.

[11] Due to this coloration, they are often mistaken both by insect-eating birds and by humans for wasps or bees; they exhibit Batesian mimicry.

[6] Bee flies of the family Bombyliidae often mimic Hymenoptera and hover around flowers, as well, rendering some bombyliid species hard to tell apart from Syrphidae at first glance.

[6][14] Predatory species are beneficial to farmers and gardeners, because aphids destroy crops, and hoverfly maggots are often used in biological control.

The genus Prosyrphus, found in Late Cretaceous (Cenomanian) Burmese amber, appears to represent a stem group to the family.

[21] While some hoverfly larvae are aquatic and are often found in stagnant water, those of species that prey upon aphids and other plant parasites are usually terrestrial, residing on leaves.

[27] Many syrphid fly species have short, unspecialized mouth parts and tend to feed on flowers that are more open as the nectar and pollen can be easily accessed.

The orchid species Epipactis veratrifolia mimics alarm pheromones of aphids which attracts pollinating hoverflies.

[29] Another plant, the slipper orchid in southwest China, also achieves pollination by deceit by exploiting the innate yellow color preference of syrphids.

[32] Larvae in the subfamily Eristalinae live in semi-aquatic and aquatic environments, including manure and compost, and can filter and purify water.

Fredrik Sjöberg's [sv] book The Fly Trap concerns his enthusiasm for hoverflies on the island of Runmarö in the Baltic Sea.