THE ACAEINA OR MITES. 



139 



Fig. 200.— Phyllocoptes sp., side view, 

 illustration.) 



(Author's 



latter has been sufficiently abundant in California to be considered injurious to the 

 trees. A ?mall roundi.'^h gall, with many folds in its interior and the orifice guarded 

 by long white hairs, is also found on the leaves of black walnut. The mites are red, 

 and were described by Nalepa as Eriophyes tristriatus. On willows there are small 

 rounded galls on the leaves formed by E. semen Walsh, and longitudinal leaf 

 folds caused by E. salicicola Garman. Inrolled loaf margins are caused by an unde- 

 termined species, and large, irregu- 

 lar deformations of the buds are 

 the results of E. aenigma "Walsh. 



Oak leaves often show an erineum 

 on the underside, wliich sometimes 

 becomes a dimple gall; on the white 

 oak it is produced by E. querci Gar- 

 man , wliile that on other oaks is prob- 

 ably the work of a different species. 

 The leaves of basswood frequently 

 have large pouch galls, which are in- 

 habited by E. ahnormis Garman. On 

 the leaves of the American elm small round galls are caused by E. ulmi Garman. On 

 the alder leaves there are often great numbers of small rounded galls produced by 

 E. brevipes Fockeu. Pouch galls on leaves of wild cherry are made by E. serotinae 

 Beutenmiiller, while minute rounded galls on the leaves of the tupelo or sour gum 

 are caused by E. nyssae Trotter. On the twigs and stems of poplar there are some- 

 times very large, irregular deformations, known to the Germans as " knospenwuch- 

 erungen." This gall is produced by E. populi Nalepa and 

 occurs throughout the Northern States from New England to 

 Colorado, where it is rather common. Eriophyes gossypii Banks 

 (fig. 279) occurs injuriously upon cotton in Montserrat and some 

 other West India islands. The mites produce galls which were 

 so numerous as to cover many leaves with a mass of irregular, 

 roughened swellings, curled and distorted. The damage in places 

 has been so severe that the cotton has been thrown into the sea. 

 The galls within are densely clothed with long hairs. Two species 

 are very injurious to the leaves of the tea plant in India and 

 Ceylon, and no good remedies have yet been de\T.sed for them. 



Family DEMODICID^. 



To this family belongs but one genus, Demodex, found in the 

 sebaceous glands and hair follicles of various mammals, includ- 

 ing man. The mite is very small, elongate, with eight short, 

 three-jointed legs, and in front a short, median, sucking 

 rostrum. The palpi are appressed to the under surface of the 

 rostrum. The abdomen is tapering, transversely striate above 

 and below, and rounded at tip. There is a large vulva 

 situate at base of the abdominal venter. The egg is fusi- 

 FiG.291.— Demodex folli- ^^^^^ and gives birth to a hexapod larva, which molts and 

 culorum. (Author's becomes octopod. Two more molts bring it to maturity. The 

 illustration.) njTnphs greatly resemble the adults, and the sexes differ but 



little. D. folliculorum Simon (fig. 291), the species found on man, was long supposed 

 to be the cause of "blackheads" and comedones on the face. Medical authorities 

 claim that the mites do not cause ' ' blackheads, ' ' and that they occur in healthy as well 

 as diseased follicles. The mites migrate over the skin to enter new glands. They 

 occur on children as well as adults, and in all parts of the world. D. phylloides 

 Csokor has been found in Canadian swine, causing white tubercles on the skin, from 



