Several carnivorous houseplants can trap and kill fungus gnats, the tiny flies that hover around your potted plants. The most effective options are sundews, butterworts, and pitcher plants, all of which lure gnats with visual or scent cues and digest them on contact. While no single plant will wipe out a serious infestation on its own, placing one or two carnivorous plants near your houseplant collection creates a living, self-sustaining trap that works around the clock.
Why Gnats Show Up in the First Place
The gnats circling your houseplants are almost certainly fungus gnats, not fruit flies. Fungus gnats are slender with long segmented antennae and spindly legs. Fruit flies are rounder, with short antennae, and cluster near ripening food rather than soil. The distinction matters because fungus gnats breed in moist potting mix, where their larvae feed on fungi and organic matter. Overwatered plants, rich compost, and poor drainage all create the damp conditions they need to reproduce. A single pot can produce dozens of adults in a few weeks.
The adults are mostly a nuisance, but the larvae can damage fine root hairs on seedlings and young plants. Carnivorous plants target the adults, breaking the breeding cycle by reducing the number of gnats that can lay eggs in your soil.
Sundews: The Most Effective Gnat Killers
Sundews (Drosera) are the top choice for gnat control indoors. Their leaves are covered in tiny hair-like structures that produce glistening, sticky droplets. To a fungus gnat, these droplets look like water. When an insect lands, it sticks immediately. The gnat’s struggling triggers the hairs to slowly bend inward, pulling the insect closer to the leaf surface, where digestive enzymes break it down into nutrients the plant absorbs.
There are at least 194 species, so you have plenty to choose from. Two stand out for indoor gnat control:
- Drosera tokaiensis: A compact rosette sundew from Japan, only 1 to 2 inches across at maturity. Its small size makes it easy to tuck next to houseplants on a windowsill or shelf. Botanical gardens have used this species directly on propagation shelves for insect control.
- Drosera binata (forked-leaf sundew): A larger species that grows into a bushy form with more trapping surface area. The variety known as multifida is particularly adaptable and a good pick for beginners. It needs strong light, so place it in a sunny window or under grow lights.
Sundews need bright light to produce their sticky “dew.” In a dim corner, the droplets dry up and the plant loses its trapping ability. A south-facing window or a spot under grow lights keeps them active. They also need consistently moist soil and do best in a tray of distilled or rainwater. Tap water contains minerals that build up and can kill these plants over time.
Butterworts: A Low-Maintenance Alternative
Butterworts (Pinguicula) work like living flypaper. Their fleshy, succulent-looking leaves are coated in a sticky mucus produced by tiny glandular hairs. This mucus does double duty: it shimmers in light to attract insects visually, and it gives off a faint fungal or moldy scent that specifically draws in fungus gnats. Once a gnat lands, it can’t pull free. The leaf margins slowly curl inward over the insect, and digestion begins.
This trapping method is especially effective for small insects like gnats and thrips. Butterworts won’t catch anything large, but they excel at picking off the tiny flies you’re trying to eliminate.
Mexican butterworts are the best group for indoor growing. They thrive on sunny windowsills, in terrariums, or under fluorescent grow lights (where many varieties blush pink or red). Their care is slightly easier than sundews because they tolerate a wider range of conditions. During summer and fall, when the plant produces its sticky carnivorous leaves, keep the soil consistently wet using a tray of water underneath the pot. In winter, many Mexican species shift to smaller, non-carnivorous succulent leaves. During this dormant phase, let the soil dry out between waterings.
Use plastic or glazed ceramic pots with drainage holes. A soil mix of peat and sand, or peat, sand, and perlite, mimics their natural growing conditions. Like sundews, butterworts need mineral-free water: distilled, reverse-osmosis, or collected rainwater.
How Many Plants You Actually Need
One small sundew or butterwort can catch several gnats a day, but a single plant won’t eliminate an established population. The math is simple: if fungus gnats are breeding faster in your soil than your carnivorous plant can catch adults, the population keeps growing. For a few houseplants on a shelf, one or two sundews placed right next to the affected pots can make a noticeable difference within a week or two. For a larger collection, you’ll want three or four carnivorous plants spread among the group.
Position matters. Place carnivorous plants as close to the gnat source as possible. Fungus gnats are weak fliers and tend to stay near the soil they emerged from. A sundew across the room won’t catch much. A sundew sitting right next to (or even in the same tray as) an infested pot will intercept gnats as they take flight.
What Carnivorous Plants Won’t Do
Carnivorous plants reduce gnat numbers, but they rarely solve the problem alone. As one botanical garden put it, sundews “may not eliminate all your insect issues, but they provide a beautiful and entertaining control option.” They’re best used alongside basic prevention: letting the top inch of soil dry between waterings, removing decaying plant material, and using well-draining potting mixes that don’t stay soggy.
If you’re dealing with a heavy infestation, yellow sticky traps near the soil surface catch large numbers of adults quickly, while carnivorous plants provide ongoing, passive control once the population is knocked down. Together, the combination is more effective than either method on its own.
Venus Flytraps: Popular but Not Ideal
Venus flytraps are the most famous carnivorous plant, but they’re actually a poor choice for gnat control. Their snap traps are designed for larger prey like beetles and spiders. Fungus gnats are so small they often walk right out between the interlocking “teeth” of the trap before it closes fully. Each trap can also only close and reopen a limited number of times before it dies, so wasting closures on tiny gnats that escape is counterproductive. Stick with sundews and butterworts for gnat-sized insects.
Quick Comparison
- Sundews: Most trapping surface area, very effective for gnats, needs bright light and constant moisture. Best for sunny spots or grow-light setups.
- Butterworts: Slightly easier care, naturally attract gnats with scent, go semi-dormant in winter. Great for windowsills and terrariums.
- Venus flytraps: Traps are too large for gnats. Not recommended for this purpose.
Both sundews and butterworts are widely available online and at garden centers that carry houseplants. They typically cost between $5 and $15. Starting with one of each gives you two different trapping strategies working simultaneously, and you get to watch the plants do their work, which is genuinely fascinating once the first gnat sticks.