Butterwort Care: The Gnat-Eating Houseplant

Butterworts (Pinguicula) are small carnivorous rosettes whose leaves are coated in a sticky, glistening mucilage. Fungus gnats, fruit flies and other tiny flying insects land on that film, stick, and are slowly digested. For an indoor gardener with a gnat problem, a few Mexican butterworts on the windowsill are the closest thing to living flypaper: they are easy, they stay small, and they do not need the bog conditions or cold winter dormancy that make Venus flytraps tricky in a house. The catch is that they are picky about three things—water, soil and light—and they change shape every winter in a way that alarms first-time growers. Get those right and they are one of the most forgiving carnivorous plants you can grow, and a natural fit for the rest of our houseplants and container gardening guide.

In this guide

1. What Butterworts Are and How They Catch Gnats
2. Best Butterworts for a Gnat-Eating Windowsill
3. Light: Bright, but Not Scorching
4. Water: The Rule That Matters Most
5. Soil and Pots
6. Temperature and Humidity
7. Feeding: Let the Gnats Do It
8. Using Butterworts Against Fungus Gnats
9. Other Plants That Eat Flies
10. Flowers and Propagation
11. Troubleshooting Common Problems
12. A Simple Year-Round Care Calendar
13. Frequently Asked Questions

What Butterworts Are and How They Catch Gnats

Every butterwort leaf carries two kinds of glands. Stalked glands secrete droplets of sticky mucilage that look like dew and attract small insects; sessile glands sit flat on the leaf surface and release digestive enzymes once prey is trapped. Some species roll the leaf edge slightly to hold larger prey, but the plant does not move fast like a flytrap. A gnat lands, struggles, gets coated, and within a day or two you will see a small black speck dissolving on the leaf. The plant absorbs nitrogen and phosphorus from its prey, which is why it can grow in nutrient-poor soils that would starve most houseplants.

There are more than 80 species, and they fall into three practical groups. Mexican (tropical) butterworts grow from rocky slopes in Mexico and Central America; they handle household temperatures and humidity and are the ones sold as gnat catchers. Temperate butterworts such as P. vulgaris and P. grandiflora come from cold northern bogs and form a dormant winter bud called a hibernaculum; they need a chilled winter rest and rarely thrive on a windowsill. Warm-temperate species native to the US Southeast, such as P. lutea, P. caerulea and P. primuliflora, are bog plants that suit an outdoor bog garden in zones 8–10 better than a pot indoors. If you are new to the group, our carnivorous plants for beginners guide compares butterworts with flytraps, sundews and pitcher plants.

Best Butterworts for a Gnat-Eating Windowsill

Stick to Mexican species and their hybrids for indoor gnat control. These are the ones you will see most often from carnivorous plant nurseries:

• P. moranensis — the classic. Broad, flat summer leaves up to 4 inches across, pink to magenta flowers, many color forms. Very tolerant of beginner mistakes.
• P. gigantea — large, upright, slightly cupped leaves; one of the best catchers because of its surface area. Purple flowers.
• P. esseriana — compact rosette under 2 inches, good for small pots and terrariums, pale pink flowers.
• P. ‘Tina’ (P. agnata × P. zecheri) — vigorous hybrid that offsets quickly and stays carnivorous most of the year.
• P. agnata — pale green to bluish leaves, white flowers with a blue tip; grows nearly year-round with little seasonal change.
• P. cyclosecta — small, silvery-purple leaves in strong light; slower but very ornamental.

For maximum catch, put two or three plants of a large-leaved type such as P. gigantea or P. moranensis right next to the pots where gnats breed. Butterworts do not lure insects from across the room; they catch what flies past them.

Light: Bright, but Not Scorching

Butterworts want more light than most foliage houseplants. An unobstructed east window is ideal; a south or west window works if the plant sits a foot or two back from the glass or behind a sheer curtain so the leaves do not bleach in the afternoon. In good light, leaves stay compact and often blush pink or red at the edges. In poor light they turn pale, stretch upward, and produce less mucilage, which means fewer gnats caught.

A small LED grow light solves the problem for north windows, kitchens and offices. Run it 12–14 hours a day with the plant 6–12 inches below a typical full-spectrum panel. Butterworts are among the easiest carnivorous plants to grow entirely under lights; many hobbyists keep whole collections on shelves. If you already run lights for seedlings or herbs, a butterwort pot placed at the edge of the tray will do fine.

Water: The Rule That Matters Most

Like nearly all carnivorous plants, butterworts evolved in mineral-poor conditions and their roots are damaged by dissolved salts. Use distilled water, rainwater, or reverse-osmosis water. A cheap TDS meter is useful: aim for under 50 ppm total dissolved solids. Softened water is worse than hard tap water because it is loaded with sodium. Bottled “spring” or “mineral” water is not safe either. Some growers in very soft-water cities get away with tap water, but you will not know until white crust builds on the soil and the plant declines over several months, so it is not worth the gamble.

How much water depends on the season. Mexican butterworts have two growth phases, and you water each differently:

• Summer (carnivorous) phase, roughly April–October: keep the mix evenly moist. Either water from the top when the surface just starts to dry, or stand the pot in a saucer with about ¼ inch of water and let it dry out before refilling. Do not leave it sitting in deep water for weeks; Mexican species are not bog plants.
• Winter (succulent) phase, roughly November–March: the plant shrinks into a tight rosette of small, thick, non-sticky leaves. Let the mix dry almost completely between waterings, often every 2–3 weeks. Overwatering a winter rosette is the most common way people rot their butterworts.

Not every Mexican species makes a dramatic winter rosette. P. agnata, P. gigantea and ‘Tina’ may stay mostly carnivorous year-round indoors; water those a little less in winter but do not let them go bone dry for long. Watch the leaves: sticky, flat leaves mean “summer rules,” small tight non-sticky leaves mean “winter rules.”

Soil and Pots

Mexican butterworts grow on limestone slopes and cliff faces, so they want a gritty, fast-draining, mostly mineral mix. Regular potting soil is a hard no: it contains fertilizer and wetting agents that burn the roots. Good mixes include:

• Equal parts perlite, washed horticultural sand, and sphagnum peat or coco coir.
• Two parts pumice or perlite, one part peat, one part coarse sand (better for growers who tend to overwater).
• A fully mineral mix of pumice, lava rock fines and a little sand, top-dressed with fine grit—popular with experienced growers because it resists rot.

Rinse sand and perlite before use, and avoid “play sand” or beach sand, which can carry salts and lime fines. If you use coir, buy a low-sodium, rinsed brand and soak it in distilled water first. Our peat moss vs coco coir guide explains the trade-offs.

Butterworts have small, shallow root systems. A 3- to 4-inch plastic or glazed pot is plenty for one plant, and a shallow bulb pan holds several. Avoid unglazed terra-cotta: minerals wick into the clay and back into the mix, and the pot dries too fast in summer. Repot every two or three years, ideally in early spring as the plant switches from its winter rosette to summer leaves.

Temperature and Humidity

This is where Mexican butterworts make life easy. They grow well between 60°F and 85°F and tolerate brief dips into the 40s and peaks into the 90s. They do not need a terrarium; ordinary household humidity of 40–60% is fine, and very high humidity in a closed container can actually encourage rot in winter. Keep them away from heating vents that blast dry hot air, and do not leave them on a windowsill that drops near freezing on January nights. Temperate species are the exception—they need about three months near 35–45°F to form and break hibernacula, which is why they are rarely sold as indoor plants.

Feeding: Let the Gnats Do It

Never add fertilizer to the soil. A butterwort sitting near other houseplants catches enough small insects to feed itself, and even a plant that catches nothing will survive, just more slowly. If you grow plants under lights in a bug-free room and want faster growth, you can sprinkle a few grains of crushed dried bloodworms or fish flakes on the sticky leaves once a month in summer. Use a tiny pinch—excess food can mold on the leaf. Do not feed during the winter rosette phase, when the leaves are not sticky and cannot digest anything.

Using Butterworts Against Fungus Gnats

A healthy butterwort will catch dozens of adult gnats, and a leaf peppered with black specks is satisfying to look at. But be realistic: the plant catches flying adults, not the larvae living in your potting soil, and gnats lay eggs fast. Butterworts are a monitoring and suppression tool, not a cure on their own. Combine them with the steps that break the life cycle:

• Let the top inch of soil in your other houseplants dry out between waterings; larvae need constantly damp mix.
• Water infested pots with a BTI (Bacillus thuringiensis israelensis) drench for several weeks to kill larvae; see our guide to Mosquito Bits for fungus gnats.
• Top-dress pots with ½ inch of coarse sand or grit so adults cannot lay eggs as easily.
• Place butterworts and yellow sticky cards right beside the worst pots.

Our full walkthrough on how to get rid of fungus gnats covers the rest. Used together, butterworts tend to keep a low gnat population from flaring back up, which is where they really earn their space.

Other Plants That Eat Flies

If you want a mixed windowsill of insect-eating plants, a few others work indoors, each with different needs. Cape sundew (Drosera capensis) is the other great gnat trap; its sticky tentacles curl around prey and it tolerates windowsill conditions, though it prefers wetter soil than a butterwort. See how to grow sundews. Venus flytraps catch larger insects but need full sun and a cold winter dormancy, which is hard to provide indoors. Tropical pitcher plants (Nepenthes) catch crawling insects and some flyers and like warm, humid, bright spots. Butterworts remain the lowest-effort choice for gnats specifically.

Flowers and Propagation

Mexican butterworts flower in late winter or spring, sending up 3- to 6-inch stalks with single violet-like blooms in pink, purple, lavender or white. The flowers are not carnivorous and are held high, away from the sticky leaves, so pollinators are not trapped. Enjoy them; flowering does not exhaust the plant.

The easiest way to make more plants is leaf pulls, done when the plant is in its winter rosette and the small succulent leaves come away cleanly:

1. Gently wiggle a healthy leaf sideways until it pops off the base intact, including the pale attachment point.
2. Lay it flat on the surface of a moist mineral mix or on damp milled sphagnum, base touching the medium. Do not bury it.
3. Cover the container loosely with a clear lid or bag to keep humidity up, and place it in bright, indirect light or under a grow light.
4. In 3–6 weeks tiny plantlets form at the base. Pot them up once they have several leaves and roots of their own.

Hybrids like ‘Tina’ also produce offsets that can be separated at repotting. Seed is possible but slow and requires hand pollination; leaf pulls are far quicker.

Troubleshooting Common Problems

Leaves are not sticky

Usually the plant is entering its winter phase, which is normal. If it happens in summer, the cause is low light or low humidity combined with heat. Move it to a brighter spot or closer to the grow light.

Plant turns mushy or black at the base

Rot from overwatering, almost always in winter. Unpot it, remove dead tissue, take leaf pulls from any firm leaves, and repot what remains in a drier, grittier mix. Water much less until spring.

Leaves pale, stretched or curling up

Too little light. Butterworts stretch upward reaching for brightness. Bleached, crispy patches mean the opposite: too much direct afternoon sun through glass.

White crust on the soil and slow decline

Mineral buildup from tap or bottled water. Flush the pot with several volumes of distilled water, or better, repot into fresh mix and switch water sources.

White fuzz or cottony bugs

Mealybugs, including root mealybugs, are the main pest. Most insecticides and oils damage the leaf glands. Remove pests with a cotton swab dipped in water, isolate the plant, and if root mealybugs are present, bare-root and repot in fresh mix. Systemic granules are used by some growers, but test on one plant first.

A Simple Year-Round Care Calendar

• March–April: plants switch to sticky summer leaves; repot if needed; resume regular watering.
• May–September: peak gnat-catching season. Keep evenly moist with pure water, bright light, no fertilizer.
• October–November: leaves shrink and lose stickiness on species that go succulent; begin cutting back water.
• December–February: dry winter rest; water every 2–3 weeks; take leaf pulls; watch for flower stalks late in the season.