These wasps are extremely rare, but surprisingly diverse, with over 90 species in 16 genera, and are known from all parts of the world.

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 of, or injecting them inside leaves.

If the caterpillar is neither attacked by another parasitoid nor fed to a vespid, the trigonalid larva fails to develop.

[9] A possible specimen is known from the mid-Cretaceous Burmese amber of Myanmar, but this differs substantially from modern members of the family, and may belong to the stem-group.

[10] Suggested relatives of Trigonalidae within Trigonaloidea include the extinct family Maimetshidae, known from the Cretaceous period.