Red spider mite
A sap-feeding mite barely visible to the naked eye, thriving in the hot dry air of a heated room or a greenhouse. The first sign is a fine pale stippling on the leaves; by the time webbing is obvious between the leaves and stems the population is large.
Caused by: Tetranychus urticae · also called two-spotted spider mite, glasshouse red spider mite
What brings it on
Hot dry air above about 20 °C with low humidity — a heated room in winter, or a greenhouse in summer. Populations build extremely fast in those conditions and slowly or not at all in cool humid ones.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Red spider mite
Checked 2026-08-13
Usually seen: March, April, May, June, July, August, September, October
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Raise humidity and keep plants from drying out. Red spider mite is fundamentally a dry-air problem, and a humid greenhouse or a well-grouped set of houseplants is markedly less affected.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Red spider mite
Checked 2026-08-13
Dealing with it once it is there
- Under glass, the predatory mite Phytoseiulus persimilis is effective and is introduced when the pest is first seen and the temperature is reliably above about 16 °C. On houseplants, wiping the leaves and raising humidity reduces numbers, and badly infested growth is best removed.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Red spider mite — biological control
Checked 2026-08-13
Signs that lead here
Each of these lists the other things that produce the same sign, and how to tell them apart.
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.
Plant-specific guides
Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.