Spider mites are among the most frustrating garden pests, because they are almost invisible — and by the time you notice the damage, there are usually thousands of them. They are tiny, sap-sucking relatives of spiders that thrive in hot, dry conditions, and they attack vegetables, fruit, roses and houseplants alike. The good news is that they are very sensitive to humidity and water, which gives you a simple and effective weapon against them.
This guide covers how to identify spider mites, what damage they cause, how they live, and how to control them without reaching for harsh chemicals.
Identifying spider mites
Spider mites are tiny — most are less than half a millimetre long, about the size of a full stop. They are usually pale green, yellow or reddish, with two dark spots on their back (the two-spotted spider mite is the most common species in gardens). You will rarely see an individual mite clearly with the naked eye, but you can see the signs of a colony.
Look for:
- Fine yellow or white stippling on leaves — tiny pale dots where the mites have sucked out cell contents
- Leaves that turn yellow, then bronze or grey, and eventually dry up and drop
- Fine silk webbing on the undersides of leaves and between stems, especially in heavy infestations
- Tiny moving dots on the underside of a leaf, visible if you hold a sheet of white paper under the leaf and tap it — the mites fall onto the paper and can be seen moving
The stippling is the most reliable early sign. If the upper surface of a leaf looks dusty or speckled with tiny pale dots, and the underside feels slightly gritty, check for mites with the white-paper test.
Spider mites are often confused with other problems. Thrips also cause silvery stippling, but thrips are larger, darker and move more visibly, and they do not make webbing. Aphids are much larger and cluster on shoot tips. Nutrient deficiency can yellow leaves, but it does not cause stippling or webbing. 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 spider mite lifecycle
Spider mites reproduce extremely fast in hot, dry weather. A female lays dozens of tiny eggs on the underside of a leaf, and in warm conditions those eggs hatch in a few days. The young mites mature in about a week and begin laying eggs themselves. In a hot summer, a generation can take as little as five to seven days, which means numbers can explode from a few mites to thousands in a fortnight.
They thrive in dry air and dusty conditions, and they hate humidity and rain. This is why they are worst in hot, dry summers, in greenhouses and on indoor plants in centrally heated rooms. They are also favoured by the use of broad-spectrum insecticides, which kill their predators — predatory mites, ladybirds and lacewings — while leaving the spider mites themselves largely unharmed.
In autumn, as temperatures fall, many spider mites turn reddish-orange and seek sheltered places to overwinter — in bark crevices, under plant debris and in greenhouse frames. In mild climates and indoors, they can remain active all year.
Damage signs
Spider mites feed by piercing individual leaf cells and sucking out the contents. Each feeding site leaves a tiny pale dot, and as thousands of mites feed, the dots merge into a stippled, dusty appearance. The leaf loses its ability to photosynthesise, turns yellow, then bronze, and eventually dries up and falls.
On tomatoes and other vegetables, heavy infestations reduce yield and can kill young plants. On cucumbers and beans, the leaves bronze and dry quickly. On roses and fruit trees, they weaken the plant and reduce flowering and fruiting. On houseplants, they are one of the commonest causes of a plant that slowly yellows and loses leaves for no obvious reason — check the undersides of the leaves before you blame watering.
The webbing appears in heavy infestations, when the mites spin fine silk to protect their colonies and to travel between leaves. If you can see webbing, the infestation is already serious and needs action.
Organic-first control, in order
Work through these steps in order, starting with the gentlest.
1. Inspect regularly. Check the undersides of leaves at least once a week in hot, dry weather, and use the white-paper test if you see stippling. Early detection is everything: a small colony is easy to deal with, a large one is not.
2. Raise humidity and spray with water. This is the single most effective control for spider mites, because they hate water. A strong jet of water on the undersides of leaves knocks mites off and raises the humidity around the plant, which slows their reproduction. Repeat every few days in hot weather. For houseplants, mist the leaves regularly and consider moving the plant to a more humid spot — a bathroom, or a tray of damp pebbles. For greenhouse plants, damp down the floor and paths on hot days.
3. Remove badly affected leaves. If a few leaves 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, and do not leave them on the ground where mites can spread to other plants.
4. Encourage beneficial insects. Predatory mites are the natural enemy of spider mites, and they are available from biological control suppliers for greenhouse use. Outdoors, ladybirds, lacewings and other predators eat spider mites, so avoid spraying anything that kills them. Planting flowers that attract predators helps.
5. Improve growing conditions. Water plants steadily and mulch to keep the soil moist — stressed, dusty plants are far more vulnerable than healthy ones. Mulching helps keep soil moisture even. Avoid over-feeding with nitrogen, which produces soft growth that mites favour, and avoid broad-spectrum insecticides, which kill predators and make the problem worse.
6. Least-toxic sprays, last. If the steps above have not brought numbers down, insecticidal soap or horticultural oil can be used. These work by contact and by smothering, so you must cover the undersides of the leaves thoroughly. Apply in the evening to avoid leaf scorch and to protect bees, and repeat after five to seven days to catch mites that hatch after the first spray. 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 for spider mites: it kills predators and the mites come back worse.
If you are unsure which product is appropriate, check your local extension service for recommendations in your area.
Prevention
Prevention is mostly about humidity and plant health. Water plants steadily, mulch to keep the soil moist, and avoid letting plants get dusty and stressed in hot weather. In a greenhouse, damp down the floor on hot days and ventilate well. Indoors, mist houseplants regularly, keep them away from hot radiators, and group plants together to raise the humidity around them.
Inspect new plants carefully before bringing them home or into the greenhouse — spider mites often arrive on a new purchase. Isolate any plant you suspect, and check it with the white-paper test before placing it among your other plants.
Keep the greenhouse and garden tidy: clear away plant debris where mites overwinter, and clean greenhouse frames and staging in winter. For houseplants, see also our guide to fungus gnats, another common indoor pest.
When is it a serious problem vs cosmetic?
A few mites causing light stippling on a few lower leaves of a healthy outdoor plant are cosmetic — raise the humidity, spray the leaves with water and let predators do the rest. It becomes a serious problem when stippling covers most of the leaves, when leaves are turning bronze and dropping, when webbing is visible, or when young plants or greenhouse crops are affected. In that case, act quickly with the steps above, and repeat the water spraying every few days until the population collapses.
Spider mites on a single rose in a garden are a nuisance. Spider mites covering a greenhouse full of cucumbers in July are a serious problem. The difference is numbers, speed of increase and the value of the crop — and weekly inspection is how you tell which one you have.
Frequently asked questions
Can spider mites kill plants? Yes, in heavy infestations — especially young plants, greenhouse crops and houseplants. They weaken the plant by destroying leaf cells, and a severe infestation can defoliate a plant entirely. Healthy, established plants usually survive a moderate population.
Are spider mites harmful to people or pets? No. They do not bite people or pets and are not poisonous. They are a plant problem, not a health problem.
Do spider mites come from the soil? They usually arrive on plants, on the wind or on clothing and tools, and they overwinter in sheltered places such as bark crevices and plant debris. They are not primarily a soil pest.
Will rain get rid of spider mites? Rain helps a lot — mites hate water and wet conditions. A wet summer usually means few spider mites. In dry weather, regular spraying with water mimics the effect.
Can I use washing-up liquid on spider mites? 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
Spider mites are tiny, fast-breeding and worst in hot, dry conditions — and they hate water. Inspect weekly, spray the undersides of leaves with water, raise humidity, encourage predators, and reach for insecticidal soap only if the gentler steps have not worked. For more pest guidance, see the guides hub and the garden tools.