MITES. 547 



are Myobiidce, small, oval mites, not unlike lice in shape, which infest mice 

 and other small mammals, and birds ; and Demodicidce, the few species of 

 which are long, tapering, microscopic mites, infesting the hair-follicles of 

 man and other animals. In man, the common Demodex follicidorum (Simon) 

 often occurs on the face, where its presence is indicated externally by a black 

 speck ; but as it is a parasite of very small size and stationary habits, its 

 presence does not cause anything like the same annoyance as that of 

 Sarcoptes scabiei. 



The Trombidiidce are a family of brown, or bright scarlet mites, which are 

 in the habit of attaching themselves to insects, to which they cling so tightly 

 that they may often be seen in numbers attached to Museum specimens. 

 They attack flies, sawflies, and other insects, but are most conspicuous 

 when attached to the wings of dragonflies in more or less symmetrical 

 rows. Some very large species, measuring nearly half an inch in length, are 

 often found pinned in miscellaneous collections of insects, etc., from 

 Africa and the East Indies. ' 



The Tetranychidce are allied to the last family, but are plant-feeders. The 

 two best known species are that great pest in hothouses, the " Red Spider" 

 (Tetranychus telarius, Linn.), which, however, is not a 

 spider, but a mite ; and the harvest bug (T. autumnalis, "Red Spiders" 

 Shaw), which burrows into the skin, causing great incon- (Tetranychus). 

 venience ; while in the case of allied tropical species, sup- 

 puration and ulceration may result in extreme cases. However, most of the 

 species of this family are harmless, living on plants, or under stones, and 

 not attacking animals. 



The last family we have to notice, the Tyroglyphidce, includes several of 

 the most typical mites, such as the cheese-mites and the sugar-mite. Tyro- 

 ylyphus siro (Linn.), the commonest of the former, abounds 

 in cheese, causing a kind of dry rot ; and the dust from such Cheese-Mites,etc. 

 a cheese, when placed under the microscope, generally proves (Tyroglyphidw). 

 to be full of mites. They are harmless when swallowed, nor 

 do they attack the skin. Other mites, belonging to the genus Cheyletus (Latr.), 

 with large claw-like palpi, feed on cheese-mites, etc. Yery small mites, 

 belonging to the genus Tyroglyphus, are among the most destructive pests in 

 collections of insects. The sugar-mite (T. sacchari, Cameron), abounds in 

 unrefined sugar, and is sometimes the cause of a complaint known as "grocer's 

 itch." Now, however, almost all sugar brought into the market is more or 

 less refined, and no longer liable to the attacks of mites. Most of the 

 Tyroglyphidce are harmless, some feeding on dried vegetable or animal sub- 

 stances, while others are carnivorous, feeding on insects ; and others, again, 

 are, or may accidentally become, parasitic. Cases of dysentery have some- 

 times been attributed to the presence in the intestines of mites belonging 

 to this family, which had been accidentally swallowed. 



ORDER VIII. TARDIGRADA. 



These are small mites found among moss and seaweed. The cephalothorax 

 and abdomen are fused together ; the body is broad, with four indistinct 

 rings on the body. The sexes are not separate. The position of this group 

 is still doubtful. 



