The family Hepialidae is considered to be very primitive, with a number of structural differences to other moths including very short antennae and the lack of a functional proboscis or frenulum (see Kristensen, 1999: 61–62 for details).

Strictly speaking, they are phylogenetically too basal and constitute Microlepidoptera, although hepialids range from very small moths to a wingspan record of 250 mm in Zelotypia.

Whilst the type locality of Eudalaca sanctahelena is from the remote island of St Helena, this is thought to be an error for South Africa.

[4] Swift moths are usually crepuscular and some species form leks, also thought to have arisen independently in the genus Ogygioses (Palaeosetidae).

In other genera, virgin females "assemble" upwind to displaying males,[10] which emit a pheromone from scales on the metathoracic tibiae.

Some species feed on leaf litter, fungi,[15] mosses, decaying vegetation, ferns, gymnosperms and a wide span of monocot and dicot plants.

[4][16] There is very little evidence of hostplant specialisation; whilst the South African species Leto venus is restricted to the tree Virgilia capensis this may be a case of "ecological monophagy".

[6] Chinese medicine makes considerable use of the "mummies" collected of the caterpillar-attacking fungi Ophiocordyceps sinensis, and these can form an expensive ingredient.

[20] However, some species of Wiseana, Oncopera, Oxycanus, Fraus and Dalaca are considered pests of pastures in Australia, New Zealand, and South America.