Fig. [240].—Vermiform Mites, highly magnified. A, Demodex folliculorum; B, Eriophyes (Phyptoptus) ribis.
The Eriophyidae are unique among Mites in possessing only two pairs of legs, situated quite at the anterior part of the body. The mouth-parts are very simple.
There are three genera, Eriophyes (Phyptoptus) with about one hundred and fifty known species, Monochetus with a single species, and Phyllocoptes with about fifty species.
Among the best known examples are Eriophyes tiliae, which produces the “nail-galls” on lime-leaves, and E. ribis, the “black-currant Gall-mite,” which feeds between the folded leaves of the leaf-buds, and gives rise to swelling and distortion.
Fam. 2. Demodicidae.—The single genus Demodex which constitutes this family consists of a few species of microscopic Mites which inhabit the hair-follicles of mammals, and are the cause of what is known as “follicular mange,” some other forms of mange being due to members of the succeeding family. Demodex possesses eight short, three-jointed legs, each terminated by two claws. The abdomen is much produced, and is transversely striated. About ten species have been described, but of these five are probably varieties of D. folliculorum (Fig. [240], A), which infests Man.
Sub-Order 2. Astigmata.
The Astigmata are Mites of more or less globular form, with chelate chelicerae and five-jointed legs. All members of the group are eyeless. Their habits are very various, some feeding on vegetable matter and others on carrion, while a large number are parasitic on animals. Tracheae are absent. There is only one family.
Fig. [241].—A, Leg of a fowl infested with “leg-scab”; B, female of Sarcoptes mutans, greatly magnified. (After Neumann.)