Spider mites on houseplants: how to spot them and get rid of them

Spider mites are tiny plant-feeding arachnids that suck the contents of leaf cells, leaving fine pale stippling, a dusty look and, in heavy infestations, silky webbing. To get rid of them on houseplants, isolate the plant, rinse the leaf undersides, then spray insecticidal soap or horticultural oil every 5–7 days for three to four rounds, because most products do not kill the eggs.

How to tell it's spider mites: the white-paper test

You don't need a microscope. Hold a sheet of white paper under a suspect shoot and tap the leaves sharply 5–10 times. Wait 10–20 seconds and look under a lamp: dust lies still, while spider mites start crawling. UC IPM describes them as "tiny, moving dots" to the naked eye, with adult females less than 1/20 inch long, living in colonies mostly on leaf undersides.

Under a 10x hand lens or a phone's macro mode, an adult has eight legs, an oval body and, in the common twospotted spider mite, a dark blotch on each side. Eggs look like clear droplets that turn cream colored before hatching.

What the damage looks like

• Stippling: hundreds of pin-sized pale dots on the upper surface, matching feeding spots below. Clemson HGIC describes it as light-colored speckling that gives the whole plant a faded look.
• Bronzing or yellowing, then leaf drop as feeding continues.
• Webbing between leaf and petiole, in branch forks and at shoot tips. Webbing means the colony is already large; most early infestations have none.

Spider mites vs. look-alikes

"White spider mites" are usually pale twospotted mites or their shed skins; very small, fast white specks in damp soil are more often springtails or soil mites (see bugs in soil). Soil mites live in the potting mix and eat decaying matter; spider mites live on the foliage.

Why spider mites are not insects, and why that matters

Spider mites are arachnids, related to spiders and ticks. Many products sold "for insects" barely touch them. UC IPM warns that spider mites often flare up after sprays of some organophosphates or pyrethroids: these kill the mites' predators but not the mites. Systemic imidacloprid granules don't control them either (see systemic insecticide).

When you shop, look for "spider mites" or "mites" listed on the label. In US stores the practical options are:

• Insecticidal soap (potassium salts of fatty acids), ready-to-use sprays.
• Horticultural oil, including neem oil (clarified hydrophobic neem extract). See neem oil on houseplants.
• Labeled miticides for houseplants, for heavy, repeat infestations.

Soaps and oils work only by contact, so coverage of leaf undersides decides the result. Colorado State Extension lists soap and oil sprays among the most useful houseplant options and notes that strong water sprays are particularly effective for dislodging spider mites.

Life cycle: why the calendar matters

The cycle is egg, six-legged larva, two eight-legged nymph stages, adult. According to UNH Extension, eggs hatch in 3 to 19 days depending on temperature, development to adult takes about 19 days in cool conditions, and miticides usually kill adults and nymphs but not eggs, so a second spray 7–10 days later is needed. UC IPM adds that in hot weather a generation can finish in less than a week.

Winter is peak season indoors. Forced-air heat drops indoor humidity to 20–30 % and a sill above a register or radiator runs hot. Spider mites thrive in hot, dry, dusty conditions and on drought-stressed plants, which is why a palm or English ivy near a heat source is so often the first victim.

How to get rid of spider mites: a day-by-day plan

For one medium plant at 70–75 °F. In a hot room shift intervals toward 5 days; in a cool room toward 7–10.

1. Day 0, isolate. Move the plant to another room, at least 5–6 feet from other pots. Run the paper test on every neighbor; mites spread on air currents, touching leaves and hands.
2. Day 0, rinse. Cover the soil with a plastic bag and shower the foliage with lukewarm water for 3–5 minutes, aiming at the undersides. This removes a large share of the mites and their webbing. Cut off leaves that are mostly stippled if the plant can spare 10–20 % of its foliage.
3. Day 0, clean around. Wipe the sill, window glass, pot, saucer and any stake or moss pole.
4. Day 1, first spray. Insecticidal soap or horticultural/neem oil at label rate. Wet the undersides until they drip. Don't spray a water-stressed plant or in hot sun; water the day before and treat in the evening or in shade. Test on one leaf first for sensitive plants such as ferns.
5. Days 2–6, check. Paper test on 2–3 shoots daily. Live mites should drop sharply within 1–3 days.
6. Day 7, second spray. Same product. This catches mites that hatched from eggs that survived round one.
7. Day 14, third spray. In a hot room do it at day 12.
8. Day 21, fourth spray only if you found any live mites in the last week. If not, stop: spraying clean plants "just in case" only selects for resistance.
9. Days 21–45, quarantine. Keep the plant apart for 3–4 weeks after the last live mite and check new growth every 4–5 days.

Wear gloves, read the label and treat in a bathroom or outdoors, away from food, aquariums and pet bowls.

If a whole windowsill is infested

With three or more infested pots, treat the whole group on the same day and the same schedule. Check hiding spots: the inner crown of palms such as parlor palm and areca palm, the inside of a weeping fig, the leaf bases of dracaena. When mites "come back," the usual reason is one untreated plant left on the same shelf.

Predatory mites

Predatory mites such as Phytoseiulus persimilis eat spider mites and are sold by mail order. Colorado State notes they are perishable and must be released soon after purchase. They need warmth, humidity of roughly 60 % or more, and a break of several weeks from sprays. They make sense for a sunroom or large collection, rarely for two or three pots.

What doesn't work and why

• Garlic, onion or tobacco teas. Short-lived repellent effect at best; the colony under the leaf keeps breeding.
• Dish soap instead of insecticidal soap. Colorado State Extension explains that dish detergents are not formulated or tested for plants and can injure foliage. Use a labeled insecticidal soap.
• One "strong" spray. Eggs survive; the population rebounds within 10 days.
• Raising the dose. Burns leaves without fixing a wrong product choice.
• Misting alone. Higher humidity slows mites but doesn't eliminate them, and constantly wet leaves invite leaf spot on calathea and prayer plant.
• Ladybugs from the garden center. Indoors they fly to the windows and die.

How to know they're gone

Old stippling never fades, since the damaged cells are dead. Judge by three checks:

• The paper test on 3–4 different shoots finds no moving specks, three times in a row, 4–5 days apart.
• Leaves that opened after the last spray are clean.
• No new webbing 10 days after you wiped forks and pot rims.

If a plant has lost over 60–70 % of its leaves and has no healthy growing tips, it is often faster to root a clean cutting and discard the rest. See propagation.

How to prevent spider mites

• Keep plants a foot or more away from heat registers and radiators in winter; aim for 40–60 % humidity (see humidity).
• Water consistently; drought-stressed plants are hit hardest.
• Rinse or wipe foliage every 2–4 weeks. It removes dust and lets you catch the first stippling.
• Quarantine new plants and gifts for at least three weeks, as Colorado State recommends for all new houseplants.
• Keep cut bouquets away from your plants for the first week.

For the bigger picture of what else attacks indoor plants, see common houseplant pests.