Spider mites are the houseplant pest most people discover too late. They are barely visible, they breed fast in warm, dry indoor air, and by the time you notice the fine webbing, the population is already large. The good news is that they can be beaten without harsh chemicals — but only if you treat repeatedly, because no spray kills their eggs.
What spider mites are
Spider mites are arachnids, relatives of spiders and ticks — not insects. The most common species indoors is the two-spotted spider mite (Tetranychus urticae). Adults are less than 1/20 inch (about 0.5 mm) long, with eight legs and an oval body, and the two-spotted mite has a dark blotch on each side. In warm, dry conditions a new generation can develop in under a week, which is why a small problem becomes a big one so quickly.
Damage is worst in hot, dusty conditions and on water-stressed plants. They favour many common houseplants, and they spread easily from one plant to another when leaves touch.
How to tell it is spider mites
- Fine speckling (stippling) — tiny pale or yellow speckles on the upper leaf surface, where mites have drained individual cells
- Dull, bronzed leaves — foliage loses its shine, turns grey or bronze, then yellows and drops
- Fine silk webbing on leaf undersides, between leaves and stems — webbing is what separates spider mites from other tiny pests such as aphids and thrips
- Tiny moving specks on the leaf undersides, visible with a 10x hand lens
The paper test: hold a sheet of white paper under a suspect leaf and tap the leaf sharply. Spider mites show up as tiny specks that start moving on the paper. UC IPM and Iowa State both describe this test, and the Missouri Botanical Garden describes it the same way.
Do not wait for visible webs to confirm an infestation — by then the damage is advanced. Check the undersides of leaves on new plants before you bring them home, and check your collection weekly in winter, when indoor heating makes the air dry.
Step 1: isolate and rinse
- Move the plant away from your other plants immediately — at least a few feet, preferably into a separate room.
- Cut off the worst leaves and bin them.
- Take the plant to a sink or shower and rinse every surface with a strong stream of room-temperature water, especially the leaf undersides. This physically removes most mites and their webbing.
- Wipe dusty leaves on nearby plants, since dust favours mites.
Step 2: spray the undersides with soap or oil
Insecticidal soap and horticultural oil only kill mites they touch, so thorough coverage of the leaf undersides is essential. Colorado State Extension calls a 2% summer horticultural oil “perhaps the most effective miticide available for home use”, while insecticidal soap is marginally effective against two-spotted spider mite and weaker through webbing — so rinse the webbing off first.
- Test on a small area a few days before treating the whole plant, and do not spray water-stressed plants or when the temperature is above 90°F (32°C).
- Use a product labelled for indoor use on your plant and your pest, and follow the label. Spray outdoors if you can, and keep pets away until the leaves are dry.
- Neem oil is another option used by many growers, but treat it as one tool among several, not a cure on its own.
Step 3: repeat for 4–6 weeks
This is the step people skip, and the reason mites “come back”. Most sprays do not kill the eggs, which hatch over the following days. Iowa State Extension advises repeating treatment every week for 4 to 6 weeks. Other guides recommend every 3–5 days for at least three treatments. Either way, keep going after the plant looks clean — stop early and the next generation re-establishes itself.
While you treat, raise the humidity and keep the plant well watered. Dry, stressed plants favour mites; a pebble tray, grouping plants together, or a humidifier all help. Do not overwater, though — soggy soil causes its own problems.
Step 4: predators, for large collections
For a plant room or a large collection, predatory mites such as Phytoseiulus persimilis are the main biological control — the RHS lists them for glasshouse red spider mite. UC IPM gives a guideline of roughly one predator for every ten spider mites. Keep sprays away from plants where you have released predators, since spinosad and some pyrethroids harm them.
What makes spider mites worse
Avoid general insecticides such as pyrethroids, carbaryl, and malathion. They kill the predatory mites that naturally suppress spider mites, and they can make an infestation worse. Spider mites also develop resistance to treatments faster than almost any other pest, so rotate between different treatments rather than using the same product every time.
Sources
- Plant Blueprint — How to Get Rid of Spider Mites on Houseplants (6-Step Plan): https://www.plantblueprint.com/the-infirmary/how-to-get-rid-of-spider-mites/
- Grove Plant Care — Spider mites vs thrips: how to tell and treat them: https://www.groveplantcare.com/plant-care/spider-mites-thrips
- Rooted Treasures Farms — The Complete Guide to Spider Mites on Houseplants: https://rootedtreasuresfarms.com/blogs/news/complete-guide-getting-rid-of-spider-mites