Adult

A small dark fly, 4-5 mm long, more delicate than the shore fly, with longer legs and antennae and iridescent wings. Often seen flying weakly around the plants, growing medium or substrate.

Larva

Small, white transparent larvae with shiny black heads and no legs, found in the growing medium around the roots or on the inside of pots when the rootball is knocked out.

Sticky trap

Sciarid fly adults stuck on a sticky trap

Damage

(Photograph pending). Sciarid larvae can damage the roots of young seedlings or tunnel into the stems of cuttings, causing poor vigour, plant wilting and collapse. They can also be secondary organisms, feeding on damaged or diseased tissue. Sciarid flies can also carry disease spores e.g. Pythium

Biological control agents

Atheta coriaria

Adult

A small black shiny 'rove' beetle, 3-4 mm long with short wings. Very mobile, tends to burrow into the growing medium but can also be seen under pots or flying. Feeds on various soil-dwelling invertebrates including sciarid fly eggs, larvae and pupae.

Larva

Small larvae, 1-4mm long depending on age, the small ones are white/cream and the larger ones are light tan in colour. Has 3 pairs of legs at the front end. Feeds on various soil-dwelling invertebrates including sciarid fly eggs, larvae and pupae.

Hypoaspis miles or H. aculeifer

(Photo pending) Ground or compost-dwelling predatory mites, up to 1 mm long. The young mites are white and the adults are pale brown with a darker brown 'shield' on the back. Very active, running over or within compost or under pots and trays, searching for prey. Will feed on many soil-dwelling invertebrates but sciarid larvae are preferred prey.

Insect-pathogenic nematodes, e.g Steinernema feltiae

(Photograph pending). The tiny worm-like nematodes are drenched onto the compost or growing medium and the nematodes enter the bodies of sciarid larvae, releasing a symbiotic bacteria which kills the larvae. The nematodes reproduce inside the remains of the larvae and the next generation of nematodes move through the growing medium to find further host insects.