Fungus gnats are tiny flies that as adults, resemble mosquitoes. Fungus gnats don't bite people, but their presence can be annoying. Their larval stage lives in wet, overly moist potting mix, where they feed on decaying matter.
The first step to managing fungus gnats is allowing the soil in your houseplants to dry out in between watering. To read more about how to manage this pest, visit the UC IPM publication Pest Notes: Fungus Gnats.