Adult fungus gnats are about 1/8 inch long with long legs and long, threadlike antennae. Larvae are about 1/4 inch long, translucent gray to white wormlike creatures with no legs and a shiny, black head.

Adult flies: Last seen in greenhouses with high humidity flying near the surface of the growing medium. Larvae: Last seen in moist soil. Young plants are most susceptible to fungus gnats. Watch for stunting and dieback.

Criminal history

Excess water and algae on floors and benches attract fungus gnats. A prime greenhouse condition for fungus gnats is relative humidity of 70 percent or higher. Egg-laying females can smell the microbial activity in fresh media, and fungus gnats are attracted to soil-borne diseases.