Bibionid larvae grow up in grassy areas and are herbivores and scavengers feeding on dead vegetation or living plant roots.

Adults of most Plecia and some species of Bibio do not eat, but subsist solely on the food taken in during the larval stage and drop steadily when in flight until they are a few inches above the ground, hovering slowly.

Adult-stage bibionids are quite short-lived, and some species of Plecia (lovebugs) spend much of their adult lives copulating.

Fossil bibionids are known questionably from the Jurassic, while some forms from the early part of the Upper Cretaceous look quite similar to modern species.

Bibionid flies are very abundant among insect fossils from the Tertiary period, and many species have been described, although often based on highly fragmentary material.

[citation needed] The genera Penthetria and Plecia were sometimes placed in a separate family Pleciidae but no support for this has been found in molecular phylogenetic studies.