PEST PROFILES: FLIES
Click on image to view larger. Fungus gnats (Sciarids)
Adults are small (1/8 inch long), fragile grayish to black flies with long, slender legs and thread-like antennae. Their wings are clear or smoky-colored with no pattern and few distinct veins. Larvae are clear to creamy-white and can grow to about 1/4 inch long. They have shiny black head capsules.
Larval stages can damage healthy roots, stunting or killing young plants even where there is no fungal food source. Prolonged infestations may cause stunted, off-colored plants or foliage. Damage may actually be more severe to young plants when the potting media or soil has been sterilized. Fungus gnat larvae may also aid in the introduction and spread of plant diseases.
Fungus gnats develop through complete metamorphosis: egg; larva; pupa; and adult. Development occurs in 2 to 4 weeks. Fungus gnats normally follow a predictable cycle of population development: The first 2 generations are the largest, followed by a leveling off or decline in numbers.