Plant care guide
Snake Plant Gnats: What They Say About Your Watering
Updated
Why does my Snake plant have fungus gnats?
Gnats around a snake plant are fungus gnats breeding in potting mix that stays moist. A snake plant should dry out between waterings, so gnats are a sign the mix is wetter than this plant wants, which also puts the roots at risk of rot.
What to do first
Stop watering until the mix is dry, empty any saucer or outer pot, and trap adults with yellow sticky cards. Check the roots if the leaves are soft or the pot stays wet. Use a Bti drench only if larvae persist.
Small dark flies around a snake plant are a nuisance, but they are also useful information. Fungus gnats breed in damp potting mix, and a snake plant is meant to dry out between waterings. Treat the gnats as a warning about the root zone, and the fix for both problems is the same.
Confirm they are fungus gnats
Clemson HGIC’s houseplant pests factsheet describes adult fungus gnats as delicate flies about 3 mm (1/8 in) long. They run over the mix or fly weakly near it, and are drawn to light, so you may see them at windows.
The UC IPM fungus gnat Pest Note describes the larvae: a shiny black head and a whitish to clear, legless body, living in the top layer of moist mix. To check, push a few chunks of raw potato, cut side down, into the mix. UC IPM says larvae are drawn to them within a few days.
University of Maryland Extension suggests covering the pot, or a nearby drain, with screen or cheesecloth for several days to find where the flies emerge (UMD: Fungus Gnats on Indoor Plants). Iowa State Extension notes they can also come from drains and condensation trays.
Why gnats matter more on a snake plant
NC State Extension says snake plant needs well-drained soil and careful watering, because the roots rot if overwatered. It advises letting the soil dry between waterings from spring to autumn, and watering only every one to two months in winter. Penn State Extension suggests a cactus mix or a mix with perlite, and watering only when the mix is dry (Penn State: Snake Plant).
Iowa State calls fungus gnats a good indicator of overwatering. Its houseplant pests guide adds that larvae feed on fungi and decaying matter, including roots that have died from overwatering. So check the plant, not just the flies:
- Leaves firm and upright, mix drying normally: the gnats are likely the main problem.
- Leaves soft, mushy at the base or falling over, mix wet for days: look at the roots now. Our snake plant root rot guide covers what to cut and how to repot.
What to do
- Stop watering until the mix is dry. Clemson says dry conditions kill the larvae. A snake plant tolerates this well; Penn State notes it can go a month or so without water.
- Empty saucers and outer pots. Clemson and Iowa State both warn against pots standing in water.
- Trap adults. UC IPM suggests small squares of yellow sticky trap on sticks in the pot. They show whether numbers are falling, though Iowa State notes they do not stop new adults hatching.
- Use Bti if larvae persist. UC IPM, Clemson and UMD list Bacillus thuringiensis subsp. israelensis (Bti) as a soil drench for larvae. UC IPM says repeat applications at about five-day intervals are commonly needed. Water it in only as far as the label requires, so the mix can dry again.
- Leave the sprays. UC IPM says insecticides are rarely warranted for fungus gnats in homes. Iowa State says insecticides are not needed once the soil is allowed to dry.
UC IPM gives a generation time of about 17 days at 24 °C (75 °F). A few adults may keep appearing for a couple of weeks after you change your watering.
Handle it safely
The ASPCA lists snake plant as toxic to dogs and cats. Its saponins can cause nausea, vomiting and diarrhea. NC State adds that the sap can irritate skin, so wear gloves if you unpot the plant to inspect the roots.
Prevent a return
- Repot in fresh, free-draining mix. UC IPM warns against incompletely composted organic matter and recommends pasteurized potting mix.
- Use a pot with a drainage hole. NC State stresses well-drained soil for this plant.
- Water to the season. Follow NC State’s spring-to-autumn and winter schedule above instead of a fixed weekly routine.
For gnat biology and treatment options across plants, see our fungus gnat guide. Fuzz on the surface often comes with the same wet mix; see moldy soil on a snake plant. More care pages are on the snake plant hub.
References
- UC Statewide IPM Program: Pest Notes: Fungus Gnats (Publication 7448)
- Clemson Cooperative Extension HGIC 2252: Common Houseplant Insects & Related Pests
- University of Maryland Extension: Fungus Gnats on Indoor Plants
- NC State Extension Gardener Plant Toolbox: Dracaena trifasciata
- Penn State Extension: Snake Plant, a Forgiving, Low-Maintenance Houseplant
- Iowa State University Extension: Diagnosing Houseplant Problems Caused by Insect Pests
- ASPCA Animal Poison Control: Snake Plant
How this guide was put together: UC Statewide IPM Program, Clemson Cooperative Extension, University of Maryland Extension, NC State Extension, Penn State Extension, Iowa State University Extension and ASPCA guidance.