Gnats are those small, restless flies that seem to appear out of nowhere around fruit bowls and houseplants. How long they actually live depends on which species you’re dealing with — anywhere from about a week to three weeks, give or take, depending on food, temperature, and moisture.
What to grab
Trappify’s yellow sticky traps catch fungus gnats and fruit flies alike — stick a few directly in potted soil or near fruit bowls and you’ll see the population drop within days.
Different gnat species, different lifespans
“Gnat” actually covers a handful of different flies — fungus gnats, fruit flies, black flies, phorid flies, eye gnats, biting midges. They look similar enough to lump together, but their habits and lifespans vary more than people expect.
Fruit flies
Around 20-25 days total, roughly three weeks to complete a full life cycle depending on food availability and temperature. Females are ready to mate just two days after reaching adulthood, and the next generation is ready to start the cycle again within three days of that — which is exactly why a fruit fly problem can go from “a couple flies” to “a real problem” in under a week.
Fungus gnats
14-17 days, and these are the ones you’ll find breeding in overwatered houseplants specifically. Larvae feed on plant roots, which is part of why a fungus gnat problem can actually stress your plants, not just annoy you. Eggs hatch into larvae roughly 3 days after being laid.
Eye gnats
11 days to about three weeks. These are drawn to organic matter and well-drained soil, and unlike most gnats, they’ll feed on perspiration, eye fluid, and open wounds — genuinely unpleasant, though not dangerous.
Black flies
Also called turkey gnats or buffalo gnats. Bite livestock, wildlife, and people. Females lay up to 450 eggs directly in running water, since larvae are aquatic and feed on small organisms in the water. Pupae take 2-6 days, and once mature, adults feed on both blood and nectar. Full cycle: up to about 4 weeks.
Biting midges
Adults live 3-4 weeks. Females lay a smaller batch than most gnats — 25-100 eggs. Larvae take about two weeks to develop, pupae another 2-3 days.
Phorid flies
Common in drains, sewer lines, and anywhere with a leaky pipe — larvae feed on the organic buildup in that kind of environment. Females can lay up to 500 eggs over a lifetime, and adults live 11-22 days depending on conditions.
What actually determines how long they survive
All gnats go through the same basic stages — egg, larva, pupa, adult — and most don’t eat as adults unless they’re actively preparing to lay eggs. The larval stage is where the real activity (and vulnerability) happens: no food during that stage, and they simply don’t survive to adulthood. Dragonflies are one of their more significant natural predators, for what it’s worth.
Moisture
Gnats need consistent water and humidity to thrive — garbage cans, overwatered plants, under sinks, leaky pipes, condensation around window vents. You’ll rarely find an established gnat population in a genuinely dry environment; moisture is basically a requirement, not a preference.
Food source
If gnats keep showing up indoors, check for organic material they can actually feed on — mold, moss, compost, fungus. Potting soil is a classic hiding spot, since they feed on decaying roots and leaf matter right where you can’t easily see it.
Does cold weather kill them?
Not outright, but it stops reproduction cold (so to speak). Below about 60°F, lifespan drops sharply. The sweet spot for a healthy gnat life cycle is 65-75°F — which, unfortunately, is also roughly room temperature in most homes year-round.
Getting rid of them
First, actually identify what you’re dealing with — small flies, long thin legs, delicate wings. Eggs are basically invisible to the naked eye; larvae are legless and tiny, often under an eighth of an inch.
Kill what’s already there
Toss any infested fruit or vegetables, hang sticky traps near problem areas, and for fruit flies specifically, apple cider vinegar works well as a DIY trap — undiluted ACV in an open jar draws them in, then seal and dispose after a couple of days. Repeat until you stop catching anything.
Remove what’s attracting them
Clear decayed material out of houseplants, fix any leaky pipes (phorid flies specifically love this), and seal cracks where water can pool and sit. Take the trash out consistently, and after watering plants, drain any excess water that collects in the saucer underneath — that standing water is exactly the kind of spot gnats are drawn to.
Bottom line
Gnats don’t live long individually — a week to three weeks depending on species — but they make up for it with fast, high-volume reproduction. A single female can lay hundreds of eggs, hatching anywhere from 4 to 30 days later. Kill off one generation without removing the moisture and food source drawing them in, and you’ll just be dealing with the next one shortly after.