What little is known about the biology of these insects indicates a remarkably improbable life history: in nearly all known species, females lay thousands of minute eggs, "clamping" them to the edges or injecting them inside of leaves. The egg must then be consumed by a caterpillar. Once inside the caterpillar, the trigonalid egg either hatches and attacks any other parasitoid larvae (including its siblings) in the caterpillar, or it waits until the caterpillar is killed and fed to a vespid larva, which it then attacks. Therefore, they are parasitoids or hyperparasitoids, but in a manner virtually unique among the insects, in that the eggs must be swallowed by a host. A few species are known to directly parasitise sawflies, however.