Hemerocallis gall midge has one generation a year. Adult midges emerge in May-June and lay eggs on the developing flower buds of daylilies.
The larvae feed inside the buds causing them to develop in an abnormally. Instead of being long and slender, infested flower buds are shortened and have an enlarged conical shape. The larvae are up to 3mm long and almost transparent, which can make them difficult to see in the watery liquid that accumulates between the petals in the base of the bud. Nearly 400 larvae have been found in a single flower bud; this is likely to be the progeny of more than one female midge.
When fully fed, the larvae go into the soil where they overwinter inside silk cocoons. Galled flower buds either rot or dry up without opening.