Spider mites

Spider mites are barely visible, breed fast in dry heated rooms, and are the pest most likely to catch you by surprise in winter.

How to tell

• Tiny pale dots on the leaves, as if they'd been pricked with a pin.
• Fine, silky webbing on the undersides of leaves and where leaves meet the stem.
• Leaves turning dull, greyish or bronze, then dry.
• Hold a sheet of white paper under a leaf and tap it: specks that start moving are mites.

Where they come from

New plants, cut flowers, open windows and clothes. At room temperature a generation takes one to two weeks, so a few mites become a colony quickly, and dry air speeds them up.

How to get rid of them

1. Isolate the plant from the others straight away, and check its neighbours.
2. Rinse the whole plant in the shower with lukewarm water, undersides included. This removes most of the mites and webbing.
3. Spray leaves on both sides with insecticidal soap or a neem-based product until they drip.
4. Repeat every 5–7 days for at least three weeks. Sprays don't kill eggs; the repeats catch each new hatch.
5. Cut off leaves that are badly damaged; they won't recover.

For large collections, predatory mites (*Phytoseiulus persimilis*) are an effective biological control and safe around children and pets.

How to prevent them

Check the undersides of leaves when you water, keep new plants apart for two weeks, raise humidity in winter, and give plants an occasional shower. Mites hate moisture.