What are gall mites?
Gall mites, also known as eriophyid mites, are minute animals usually less than 0.2mm long when fully grown. They have elongate bodies and two pairs of legs, unlike other mites which have four pairs. Their size means they can usually only be seen with the aid of a microscope. Their presence is readily detected by the distinctive abnormal plant growths induced by their feeding activities.
There are many species of eriophyid mite which are usually host specific this means that each species of mite will only feed on a single, or several closely related, plant species.
Eriophyid mites feed by sucking sap but while doing so secrete chemicals into the plant tissue that converts some of the normal (parenchyma) plant cells to meristem tissues which can give rise to a range of growth forms. These then grow to produce the gall. The mites can then suck sap from plant cells lining the gall structure, which are invariably more nutritious than unaffected tissue, but often do not cause serious damage to the plant.