Fungus Gnats- What Are They And How To Get Rid Of Them

10/09/2011 01:44 pm ET | Updated Oct 11, 2012

Q: I have these flying bugs hanging out around my indoor plants and its driving me crazy. It is as if they are just coming from the soil but i do not see them congregating on the actual plants. What are they?
A: It sounds like you have fungus gnats. They are small flies that develop in the growing medium of your houseplants. They are a minor pest nuisance and harmless but I do understand how annoying they can be. They hang out around your houseplant flying in erratic patterns and lay their larvae in the top couple inches of your houseplants soil. They have a short life cycle (7-10 days) but as long as they have an attractive moist soil they will lay eggs and the cycle continues.

Q: How did I get them? I just moved some of my plants in from outside, did that have anything to do with it?
A: The gnats easily colonize in soil outside, laying eggs in the cracks of your planting medium. When you bring your plants inside these colonies can come with your plant. When you move your plants from outside to in, take the opportunity to replant them in new soil - this will lessen the chance of fungus gnats being a problem in your household. Fungus gnats do fly and could find other ways to get in to your home and target wet soil.

Q: So know that I have them how do I get rid of them organically?
A: Since the gnats are attracted to moist soil to lay their eggs you can let the top couple of inches of your plants soil surface dry so that they do not continue to colonize. If you have a plant that requires consistent moisture levels to thrive this might not be the most practical option since you might be putting your plant through risk. Another option is using beneficial nematodes which brings with it a little more confidence then trying to play the guessing game.

Q: What are beneficial nematodes?
A: Beneficial nematodes are the good guys. They are living microscopic round worms that occur naturally in soil. They will attack the fungus gnat larvae and keep going until all are destroyed thus breaking the nuisance cycle. They can be purchased at most garden centers and kept cool until ready to use. The soil needs to be moist when you apply the nematodes.

Q: Can they come back again?
A: When there is nothing left for the beneficial nematodes to eat they will die as well, so there is a chance that you might get a completely new infestation in the future. Keep your nematode jar in the refrigerator and use as needed. If you transfer them to another container make sure there are some holes in the vessel so that they can breath. They can keep for a couple of months if stored properly. Use when you need to for a fungus gnat free zone. The gnat larvae feed on plant debris so as a preventative measure remove any decaying plant material as you see it.

Flickr photo by jlucier