Erineum
Guides
Acalitus brevitarsus
Alder erineum mite
Acalitus brevitarsus is an eriophyid mite that induces distinctive galls on alder species (Alnus). The mite lives and feeds within erineum—dense mats of hair-like structures—on the lower leaf surface, causing pale, domed swellings on the upper surface. It overwinters in old cones and bark crevices during autumn. The species is known from Europe, ranging from Spain to Russia.
Aceria
gall mites, eriophyid mites, four-legged mites
Aceria is a large genus of eriophyid mites (family Eriophyidae) containing over 900 described species. These microscopic, worm-like arachnids are obligate plant parasites that induce distinctive plant growth abnormalities including galls, erinea, and witches' brooms. Some species are economically significant agricultural pests, while others have been deployed as biological control agents against invasive weeds. The genus exhibits extreme host specificity, with most species restricted to a single plant species or genus.
Aceria calaceris
Rocky Mountain maple felt mite
Aceria calaceris, the Rocky Mountain maple felt mite, is an eriophyid mite that induces distinctive felt-like galls called erinea on maple leaves. This microscopic species was first described by Hartford H. Keifer in 1952 from Fallen Leaf Lake. It has a complex life cycle involving two female morphs—protogynes for reproduction and deutogynes for overwintering—plus a single male form. The species is found in the western United States and Canada, where it specializes on three maple species.
Aceria erinea
Walnut Blister Mite
Aceria erinea is a gall-forming eriophyid mite that induces characteristic blister-like galls on the leaves of common walnut (Juglans regia). First described by Alfred Nalepa in 1891, this microscopic arachnid is a specialized plant parasite with a highly restricted host range. The mite's feeding activity causes distinctive erineum galls—fuzzy, felt-like patches on leaf surfaces. Like other eriophyid mites, it has a worm-like body with only four legs and undergoes rapid development, completing its life cycle in approximately one to two weeks under favorable conditions.