The Tachinidae are a large and variable family of true flies within the insect order Diptera, with more than 8,200 known species and many more to be discovered.

[2] Reproductive strategies vary greatly between tachinid species, largely, but not always clearly, according to their respective life cycles.

Larvae (maggots) of most members of this family are parasitoids (developing inside a living host, ultimately killing it).

[6] Probably the majority of female tachinids lay white, ovoid eggs with flat undersides onto the skin of the host insect.

In a closely related strategy some genera are effectively ovoviviparous (some authorities prefer the term ovolarviparous[8]) and deposit a hatching larva onto the host.

[11] Yet another strategy of oviposition among some Tachinidae is to lay large numbers of small, darkly coloured eggs on the food plants of the host species.

[12] Conversely, certain tachinid flies that prey on useful insects are themselves considered as pests; they can present troublesome problems in the sericulture industry by attacking silkworm larvae.

Adult tachinids are not parasitic, but either do not feed at all or visit flowers, decaying matter, or similar sources of energy to sustain themselves until they have concluded their procreative activities.

As many species typically feed on pollen, they can be important pollinators of some plants, especially at higher elevations in mountains where bees are relatively few.

It is largely based on morphological characters of the adult flies, but also on reproductive habits and on the immature stage.

Some Tachinidae are generalists; for instance, Compsilura concinnata uses, at least, 200 different hosts, and thus are less safe to be used as biological controls because they will attack non-pest species, resulting in population decline.

[17] The oldest known putatively tachinid fossil (Lithexorista) dates from the Eocene Green River Formation in Wyoming.