Eriophyid mites induce plant galls. These galls develop from epidermal cells that are infected by growth regulators injected by the mites. Each species of mite has particular chemicals that cause galls to form which are of specific benefit to the mite. After the induced change has altered the behavior of the affected cell or cells, the mite does not have to remain on the site to insure continuation of gall growth. Eriophyid galls occur on soft plant parts, usually on green tissue that was infested when the plant was young.
Galls occur in many different shapes.
These include pouch or purse, bladder galls, nail galls, finger galls and head galls. Sampling For detection of spider and false spider mites , a 10X to 15X magnifying glass is a necessity. Examine the undersides of the leaves closely for mites, cast skins and webbing. A more efficient technique is to place a sheet of white typing paper beneath the leaves and strike the foliage sharply. The mites will fall onto the paper and can be more easily observed and identified than on the green foliage.