Spider mites are members of the Acari (mite) family Teranychidae. They generally live on the undersides of plants, where they spin webs and cause damage by puncturing plant cells to feed. Some spider mites feed on a broad range of plants others have a limited host range.

Beech red spider mite (Eotetranychus fagi) is specific to beech (Fagus sylvatica) and was first discovered in Britain in 2004. Adult mites are less than 1mm in length and are normally a pale greenish yellow rather than red as the name suggests.

Infestations cause fine pale yellow mottling (bronzing) of the upper leaf surface which is usually concentrated along larger leaf veins. The undersides of leaves can be covered with black excrement spots and are littered with cast mite skins and egg shells giving a dusty appearance.

Beech grown as a hedge tends to be more vulnerable to this mite than standard trees.

It is likely to have several generations during the summer months and will overwinter on the bark as eggs.

Although the damage caused by the mites can look unsightly by late summer, it unlikely to affect the long term health of infested trees and can be tolerated. This is fortunate as the pesticides available to home gardeners are unlikely to be effective and it is not practical to spray large trees or hedges.