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The spider mite life cycle starts with a small round egg. There are three active larval stages, each separated by a resting stage before the final molt to adult. The life cycle of spider mites is temperature driven and proceeds more rapidly at warmer temperatures. At 25ºC it takes about 9 days for a spider mite to mature. Females may live for up to 4 weeks and lay up to 100 eggs. Because of their short life cycle, spider mite populations can increase very rapidly in hot weather. For example, the potential progeny of one female mite in one month increases from 20 at 15.5ºC, to 12,000 at 21ºC, to 13 million at 26.5ºC!
Spider mites are usually found in colonies on the underside of the leaves where they are protected from rain (which washes them off) and where temperatures are moderated. The mites spin silk which they attach to leaf veins and which protects the eggs and adults from predators.
Spider mites feed on epidermal cells on the underside of leaves. The mites penetrate the cells with their stylets and suck out the cell contents. This mechanical injury to the cells results in light colored punctures that, when the feeding is severe, cover large areas of the leaf and result in drying of the leaves and defoliation. Photosynthesis is reduced due to damage to the chloroplasts. One species, T. turkestani, injects a toxin that causes severe damage to the plant in addition to mechanical injury and makes it the most destructive species. The population density of the mites, species involved, duration of infestation, and environmental factors all affect the potential damage to the crop.