Tiny little flies buzzing around my houseplants; it’s not the welcome home committee I’d wanted. Fungus gnats, or compost flies, are small, dark, short-lived gnats that love houseplants. The adults are annoying but harmless; the larvae, however, feed off the roots of houseplants. They are particularly fond of tender roots, fungus and other rotting material. An infestation can do considerable damage to seedlings, young plants and cuttings. Often it’s a sign that you’ve been overwatering and the roots are rotting a little. You can put out yellow sticky traps to catch the adults, but you may trap pollinators, too.
The best solution is to grow butterwort. Pinguicula (pings for short) are a genus of carnivorous plants that have sticky, glandular leaves that trap and eat their prey. Look closely and you’ll see little gnats struggling away, much like the yellow sticky trap, except more exciting. The leaves emit a faint rotting smell that attracts insects to the glistening pools of digestive enzymes. They get stuck and the plant turns them into a digestive soup to sup.
Like all carnivorous plants, pinguiculas do this to supplement their diet: they live in soils with poor mineral content. Their pretty flowers attract different flying insects from their leaves, so they never trap their pollinators.
The name butterwort comes from the Latin pinguis, meaning fat, referring to the fleshy leaves. The most common are Mexican butterworts with leaves up to 10cm long and cute, violet-like, pinky-purple flowers. These make great houseplants. They like warm conditions all year round, but can go outside in summer. They can grow in full sun or shade, but do best somewhere in between. In full sun the leaves often turn brilliant pink, but watering can be an issue in strong light because the leaves scorch if splashed. Come winter, they ditch their sticky leaves for succulent ones, surviving with little or no water; the compost just has to remain damp.
Like other carnivorous plants, they do not like alkaline conditions and are happiest drinking rainwater. It’s easiest to water them from below, draining off any excess after a couple of hours.
They are easy to propagate. Gently pull off a leaf and nudge the end into some very free-draining compost (add lots of perlite). New babies will appear at the end of leaf after a couple of weeks.
