How to Get Rid of Fungus Gnats

Confirm you have fungus gnats

Start by confirming the bug. Fungus Gnats have a few features that set them apart. Adults measure 2–4 mm (up to about 0.16 in) and are usually black and gray. Look for these features:

• Delicate dark body with long legs and antennae
• Weak, erratic flight near plants
• Y-shaped vein pattern in the wings

They are most often confused with fruit fly, mosquito and drain fly. See the full fungus gnat profile for side-by-side details.

Why you have fungus gnats

Fungus Gnats come indoors looking for food, water, warmth or shelter. Gaps around doors, windows, pipes and utility lines give them easy ways in. Clutter, leaks and food left out let a small problem grow into an infestation. They are most active in spring, summer, fall and winter, so expect to see more of them then.

When you'll see fungus gnats

Fungus Gnats are most active in spring, summer, fall and winter. In spring, overwintering adults become active and many species lay their first eggs. Summer heat speeds up development, so populations can grow quickly. In fall, many bugs look for shelter, and some move toward or into buildings. In winter, activity continues mainly indoors in heated spaces.

Typical places to check: indoors, anywhere.

Step-by-step: getting rid of fungus gnats

Step 1: Let the top inch of potting soil dry out between waterings

Let the top inch of potting soil dry out between waterings. Repeat this for at least two to three weeks, since eggs and hidden insects keep appearing for a while.

Step 2: Use yellow sticky traps to catch adults

Use yellow sticky traps to catch adults. This is the step most people skip, and it is the one that makes the biggest difference.

Step 3: Treat soil with Bti (mosquito bits) to kill larvae

Treat soil with Bti (mosquito bits) to kill larvae. Keep notes on where you still see activity so you can focus your effort.

Natural and low-toxicity options

These methods work well alongside the steps above and keep chemical use to a minimum:

• Vacuum insects and egg cases, then empty the canister outdoors right away.
• Wipe surfaces with soapy water to remove scent trails and residue.
• Place sticky traps to find out where activity is highest.
• Run a dehumidifier where damp areas attract them.

If you do use a pesticide, choose one labeled for this pest and the place you're treating, and follow the label exactly. The label is the law.

When to call a professional

Call a licensed pest control company if you still see fungus gnats after three to four weeks of steady effort, if they are spreading to several rooms, or if you share walls with neighbors who have the same problem.

How to keep fungus gnats from coming back

• Seal cracks and gaps with caulk and install door sweeps.
• Store food in sealed containers and take out trash often.
• Fix leaky pipes and faucets and keep basements dry.
• Trim shrubs and branches so they don't touch the house.
• Keep firewood, mulch and debris away from the foundation.

Safety notes

Fungus gnats don't bite; larvae can damage seedlings and young roots.

Keep children and pets away from any traps, baits or treated areas.

About flies & mosquitoes

The fungus gnat is one of the flies & mosquitoes. Flies have only one pair of working wings; the second pair is reduced to small balancing knobs called halteres. They go through complete metamorphosis, and the larvae, called maggots, need moist organic material such as garbage, soil, drain film or standing water.

Fly problems are almost always breeding-site problems. Finding and removing the moist material where larvae develop works far better than swatting adults.

Frequently asked questions