Similar to those of some osmylids (Osmylidae) at first glance, they have spindly legs on a bulky thorax, long antennae, and flexible, threadlike mouthparts.

The females deposit their eggs singly or as small clutches on plants that droop over freshwater lakes or slow-moving rivers.

Spongillafly larvae leave the water and go to hidden places nearby to pupate, choosing locations like beneath rocks or behind tree bark.

But this is apparently due to convergent evolution; actually, the spongillaflies seem to be closer to the brown lacewings (Hemerobiidae) than to the osmylids, but even more closely related to the dustywings (Coniopterygidae).

[1] The genus Cratosisyrops, from the Aptian Crato Formation, was suggested to be a spongillafly member, but later authors Perkovsky and Makarkin in 2015 noted the fossil lacks details to confidently place it in the family.