Thrips are tiny, slender insects that cause silvery streaks and distorted growth on a wide range of plants, and they are one of the hardest pests to see — most are only 1–2 mm long, about the size of a comma. They attack vegetables, flowers, fruit and houseplants, and they are a particular problem in greenhouses and indoors. They are also virus carriers, which makes them more dangerous than their size suggests. The good news is that they are sensitive to water and to predators, and a combination of methods can keep them in check.

This guide covers how to identify thrips, what damage they cause, how they live, and how to control them organically.

Identifying thrips

Thrips are tiny, slender, dark brown, black or pale yellow insects, 1–2 mm long, with narrow, fringed wings. They are hard to see with the naked eye, but they are visible if you look closely at a damaged leaf, or if you tap a flower over a sheet of white paper and watch for tiny, dark, moving specks.

Look for:

  • Silvery or bronze streaks and speckles on leaves, where the thrips have sucked out cell contents
  • Leaves that are distorted, curled or stunted, especially new growth
  • Flowers that are deformed, streaked or fail to open properly
  • Dark specks of droppings on the leaves and petals
  • Tiny, slender insects on the leaves and in the flowers, visible with a hand lens or on white paper

Thrips are sometimes confused with other pests. Spider mites also cause stippling, but they are smaller, cause finer dots and produce webbing. Aphids are larger, pear-shaped and cluster on shoot tips. If the damage is silvery streaks and distortion, and you find tiny, slender insects in the flowers, it is thrips. If you are unsure, our pest identifier helper can help you work through the symptoms, and your local extension service can confirm an identification.

The thrips lifecycle

Thrips reproduce quickly in warm conditions. The female lays tiny eggs inside the leaf or flower tissue, where they are protected from sprays. The eggs hatch into small, wingless larvae that feed on the leaves and flowers for a week or two, then drop to the soil or hide in a sheltered place to pupate. The adults emerge a few days later and fly to new plants.

In a warm greenhouse, the whole cycle can take as little as two to three weeks, and there may be several overlapping generations at once — eggs, larvae, pupae and adults all present on the same plant. That is why a single spray rarely solves the problem: it may kill the adults and larvae but leave the eggs inside the leaf tissue and the pupae in the soil untouched, and a new generation appears within days.

Outdoors, thrips are worst in hot, dry weather and die back in cold weather, though they can survive mild winters in sheltered spots. In greenhouses and indoors, they can remain active all year.

Damage signs

Thrips damage plants by piercing individual cells and sucking out the contents, which leaves a silvery or bronze streak where the cell has collapsed. On leaves, this shows as silvery speckles and streaks, often along the veins. On flowers, it shows as deformed, streaked petals that fail to open properly. On fruit, it can cause silvery scarring and distortion.

The crops most affected include onions — onion thrips are a major pest, causing silvery leaves and reduced bulb size — as well as tomatoes, peppers, cucumbers, beans and many flowers, especially roses, gladioli and dahlias. On houseplants, thrips cause silvery leaves and distorted new growth, and they are one of the commonest causes of a plant that slowly declines for no obvious reason.

Thrips also spread plant viruses, including tomato spotted wilt virus, which affects tomatoes, peppers and many other crops. There is no cure for a virus-infected plant, which is why thrips should be taken seriously even when the direct feeding damage looks light.

Organic-first control, in order

Work through these steps in order, starting with the gentlest. Thrips control takes persistence — expect to repeat the steps for several weeks.

1. Inspect regularly. Check the leaves and flowers at least once a week in warm weather, and tap flowers over white paper to check for thrips. Early detection is essential, because the lifecycle is fast and overlapping generations make late control much harder.

2. Use blue sticky traps. Blue sticky cards attract thrips — they are more attracted to blue than to yellow — and they catch adults, reduce numbers and show you how bad the problem is. Hang them just above the plants in a greenhouse, or near affected houseplants. Traps alone will not control a heavy infestation, but they are an essential part of the control programme.

3. Spray with water. A strong jet of water knocks thrips off the leaves and raises the humidity, which slows their reproduction. Repeat every few days. For houseplants, a regular shower under the tap or in the shower can help a lot.

4. Remove badly affected leaves and flowers. If a few leaves or flowers are heavily infested, remove them and drop them in a bucket of soapy water or a sealed bag — do not compost them in a cold heap. This removes a whole generation at once.

5. Encourage beneficial insects. Predatory mites, lacewings and pirate bugs all eat thrips, and they are available from biological control suppliers for greenhouse use. Outdoors, ladybirds, lacewings and other predators eat thrips, so avoid spraying anything that kills them. Plant flowers that attract predators, and leave some habitat.

6. Improve growing conditions. Keep plants healthy with steady watering and moderate feeding, and avoid overcrowding — good airflow makes plants less attractive. Mulching helps keep watering steady. Avoid heavy nitrogen fertiliser, which produces soft growth. Our fertiliser calculator can help you avoid over-feeding.

7. Least-toxic sprays, last. If the steps above have not brought numbers down, insecticidal soap or horticultural oil can be used, but they are only partly effective against thrips because the eggs are inside the leaf tissue and the pupae are in the soil. Apply thoroughly, covering the undersides of leaves and the flowers, in the evening to avoid harming bees and to reduce leaf scorch, and repeat every five to seven days for at least three weeks to catch each new generation as it emerges. Spinosad, a naturally derived insecticide, is effective against thrips in some areas, but it is also toxic to bees when wet, so apply it in the evening when bees are not active and only if it is approved in your area. Always read and follow the label, use only products approved for the crop in your area, and wash produce before eating. Never use a broad-spectrum insecticide: it kills the predators that control thrips.

If you are unsure which product is appropriate, check your local extension service for recommendations in your area.

Prevention

Prevention is mostly about inspection and hygiene. Check new plants carefully before bringing them into the greenhouse or the house — thrips often arrive on a new purchase. Isolate suspect plants and check them for a week before placing them among your other plants.

Keep the greenhouse tidy: clear away old plant material where thrips can breed, and clean the greenhouse in winter. Ventilate well in summer, and use blue sticky traps as an early-warning system even when you do not have a problem. For houseplants, keep them in good light with steady watering, isolate any plant with thrips, and check the leaves and flowers weekly. See also our guide to fungus gnats, another common indoor pest.

When is it a serious problem vs cosmetic?

A few thrips causing light silvering on a few leaves of a healthy outdoor plant are cosmetic — the plant will cope, and predators and weather will keep numbers down. It becomes a serious problem when leaves and flowers are badly distorted, when growth is stunted, when fruit is scarred, or when greenhouse crops or young plants are affected. In a greenhouse, even a moderate population should be taken seriously, because the warm, sheltered conditions let numbers build fast and the virus risk is real.

Thrips on a single outdoor rose are a nuisance. Thrips covering a greenhouse full of cucumbers, or thrips on onions that are silvering the whole crop, are a serious problem. The difference is numbers, speed of increase and the setting — and weekly inspection is how you tell which one you have.

Frequently asked questions

What do thrips look like? Tiny, slender, dark or pale insects, 1–2 mm long, with narrow fringed wings. They are hard to see without a hand lens, but they are visible as tiny moving specks on white paper tapped from a flower.

Do thrips bite people? Some species can bite, causing a mild, temporary irritation, but they do not feed on people and are not dangerous. They are a plant problem, not a health problem.

Will thrips go away in winter? Outdoors, cold weather kills most of them, though some survive in sheltered spots. In a greenhouse or indoors, they can remain active all year, so winter is the time to clean the greenhouse and break the cycle.

Are thrips the same as spider mites? No. Spider mites are smaller, cause finer stippling and produce webbing. Thrips cause silvery streaks and distortion, and they are larger and more visible. See our guide to spider mites on plants.

Can I use washing-up liquid on thrips? It is sometimes recommended as a home remedy, but washing-up liquid is not formulated for plants and can damage leaves, especially in sun. Insecticidal soap, made for the purpose and used at the label rate, is safer and more reliable.

The bottom line

Thrips are tiny, fast-breeding and hard to see, but they can be controlled with persistence: inspect weekly, use blue sticky traps, spray with water, remove infested leaves, encourage predators, and use insecticidal soap only if the gentler steps have not worked. For more pest guidance, see the guides hub and the garden tools.