The adult hemerocallis gall midge is a small fly – or midge. The female flies lay their eggs in the developing flowers buds of daylilies in May and June. These hatch into larvae, which feed inside the buds, causing abnormal flower development. Hundreds can be found in each flower bud.
The larvae look like almost transparent, small maggots, up to 3mm (less than 1/8in) long. As they feed, a watery liquid develops inside the bud, often making it difficult to see the larvae.
Once fully fed, the larvae drop into the soil and overwinter inside silk cocoons. The adult midges emerge in May-June and the lifecycle repeats again. There is just one generation per year.
The first hemerocallis gall midges were recorded in the UK in 1989, and have since spread to many parts of the UK.