290 Forty-second Report on the State Museum. [148] 



beetle, and, as in the present instance, to render valuable service in 

 reducing the numbers of this pest. Its principal interest, perhaps, 

 is in the fact that, up to the present, only two or three true parasites 

 of this beetle have been discovered among its thirty or more known 

 natural enemies. 



As an aid in the recognition of this parasite, it may be stated that 

 they are quite minute forms, as five of them placed closely together 

 would not exceed in surface that of the head of an ordinary pin. 

 Their color is yellowish-brown, and in general shape they resemble 

 many of the lady-bugs {Coccinelhdce), being oval, flat beneath and 

 convex above. When examined with a microscope, they are found to 

 possess eight legs, and this feature, of course, removes them from the 

 lice and all other true insects, which have but six legs. 



Their scientific classification places them among the Arachnoidea, 

 in which are included scorpions, spiders, and mites. As their body 



consists of but one piece, instead of being 

 made up of several segments, they fall in 

 the last-named order, the mites (Acarina). 

 This order embraces a large number of 

 greatly differing forms that have been ar- 

 ranged in several families to include, 

 follows : The spinning and the harvest mite^ 

 \\ m^^M^m _^ {Trombididce), the snouted mites (Bdellidce), 



fresh-water mites (Hydrachnidce), parasitic 

 Fig. 48.— The chicken-louse, mites (Gamasidce), the ticks {Ixodidce), the 

 DEKMANTssusAviuM-eDiarKed.i^gg^.lg_j^i^gg (^OribaUdce), the cheese-mites 



{Tyroglyphidce), \ic\i-m\ies, {Sarcoptidce), gall and bud-mites (Phytoptidce), 

 and others. The particular family to which this potato-beetle parasite 

 belongs is the Gamasidce, nearly all the species of which, in their wide 

 distribution, live parasitically on mammals, fishes, birds, and 

 insects. The common " chicken-louse," Dermanyssus avium, shown in 

 Fig. 48, which is also found on caged canary birds, is a well-known 

 species of this family. 



From examples taken from some Colorado potato-beetles in Ohio, 

 in 1873, this little Gamasid mite was described and named by Pro- 

 fessor Riley as Uropoda Americana. It was found to be closely allied 

 to a species that had long been known to infest beetles in Europe — 

 the Uropoda vegetans, having the same habit of attaching itself to its 

 host by a chord or filament, one end of which was fastened to the 

 anal end of the mite and the other to the beetle. Many had been the 

 surmises of the nature and object of this singular attachment in the 

 European species. Some of the old wi'iters had regarded it as a kind 



