Poinsettias are the most popular houseplants for Christmas in the…
Fungus Gnats are tiny insects that live in the soil of houseplants. Their larva feed on plant roots and the adults can be a nuisance when they fly around the plants. However, they don’t bite humans. They are fairly easy to ID since they are so small and completely black. Their lifecycle is usually completed in around 10 days under normal indoor conditions. The larva are usually found in the top 2 to 3 inches of a houseplant’s moist potting mix, especially those high in peat moss.
Fungus Gnats can often be controlled by simply letting the top 2 inches of the potting mix dry out before watering again. This is often good for the houseplants themselves as most don’t want to stay constantly moist. Occasionally repotting houseplants to “freshen up” potting mix that has broken down can also help control fungus gnats. If the gnats are still a problem after these measures are taken, a product containing permethrin can be sprayed on the surface of the soil to kill the adults as they emerge. Bonide’s “Systemic Houseplant Insect Control” can also kill the larva.