Caterpillars are an occasional but destructive houseplant pest, and the damage they do is out of all proportion to their numbers. A single caterpillar can chew through leaves overnight, leaving ragged holes and dark pellets of frass behind. They are most common on plants that have spent summer outdoors, but they are manageable once you know what to look for.
Life Cycle of Caterpillars
Understanding the cycle explains why they appear so suddenly. An adult moth lays eggs, usually on the undersides of leaves. The eggs hatch into small caterpillars that feed constantly and grow quickly, moulting several times. After a couple of weeks of feeding, they pupate, often in the soil or a sheltered spot, and later emerge as adult moths. The feeding larval stage is the one that damages your plants, and it is the stage you need to interrupt.
Identifying Caterpillars
Physical Characteristics
Look for soft-bodied larvae with a distinct head and several pairs of legs, moving in the characteristic looping or crawling motion. Green species blend in with foliage and are easiest to find by looking for the damage first, then searching nearby. Frass, the small dark droppings they leave, is often the first clue, collecting on lower leaves or the soil surface.
Where to Look
Check leaf undersides, new growth, and the crevices where leaves meet stems. Caterpillars often feed at night and hide during the day, so inspect after dark with a torch if you can see damage but not the pest.
Where Do Caterpillars Come From?
The usual entry point is an open window or door in summer, letting an adult moth in to lay eggs. Far more often, they arrive on plants that have spent the warmer months outside. If you move houseplants out for summer, as many people do in the UK, check them thoroughly before bringing them back in.
Damage Caused by Caterpillars on House Plants
Caterpillars eat leaf tissue, leaving irregular holes, chewed edges, and sometimes whole leaves stripped back to the midrib. On a large plant this is cosmetic; on a small or young plant a single caterpillar can do serious harm in a night or two. Because they feed fast and hide well, the damage often appears before you ever see the pest. They do not transmit disease the way some sap-sucking pests do, but the open wounds they leave can be an entry point for rot.
How to Get Rid of Caterpillars
Immediate Steps
For caterpillars, physical removal is the most effective first step, because their numbers are usually small.
- Isolate the affected plant so any caterpillars cannot move to their neighbours.
- Pick the caterpillars off by hand and remove them. Wear gloves if you prefer, as a few species can irritate skin.
- Check leaf undersides for clusters of eggs and wipe them off.
- Inspect again after dark for the ones that hid during the day.
Natural Treatments
If hand-picking is not keeping up, an insecticidal soap knocks back small caterpillars and is gentle on the plant. Zero-in Horticultural Soap is a potassium-salt soap that works on contact. Neem-based products, such as our natural leaf shine made with neem oil, also deter feeding. Apply to the undersides of leaves where eggs and young larvae sit, and repeat after several days to catch any that have newly hatched.
Biological Controls
The most targeted biological option is Bacillus thuringiensis (Bt), a naturally occurring bacterium that affects caterpillars specifically and leaves everything else unharmed. It is widely available as a garden product and is the gentlest way to deal with a larger outbreak.
When to Reach for a Stronger Control
For a heavy infestation on a robust plant, a ready-to-use insecticide such as Provanto Ultimate Bug Killer will clear them. Use it as a last resort, follow the label, and avoid spraying anything in flower that pollinators visit. You will find the full range in our pest and fungal control collection.
Prevention
Prevention is mostly about keeping egg-laying moths away and catching arrivals early.
- Quarantine any plant that has been outdoors, and any new plant, for a couple of weeks before it joins the rest. See why you should quarantine new houseplants.
- Inspect plants regularly, especially leaf undersides and new growth.
- Use fly screens on windows you leave open in summer if moths are a recurring problem.
- Deal with damage promptly. The sooner you spot frass or holes, the fewer caterpillars you will have to remove.
Caterpillars look alarming, but they are one of the more straightforward pests to control, because they are large enough to remove by hand and rarely arrive in great numbers. To brush up on the wider picture, our overview of the most common houseplant pests is a useful companion.