Genus Tarsonemus Canestrini and Fanzago 1876. Tarsonemus sauli. This species is stated by Gedoelst to have been found in tumours of certain animals-viz., the horse, dog, and mouse. Fig. 56 shows the characteristics of a Tarsonemus. FIG. 56.—TARSONEMUS LATUS (AFTER BANKS). FAMILY CHEYLETIDÆ Palpi of three to five segments thickened at the base; with lateral movement; the last article often has two combs. Mandibles long and needle-like. The body is generally oval. Legs short, five-jointed, and usually end in two claws with a bunch of hairs or bristles between them. Some species are predaceous and others parasitic. Genus Cheyletus Latreille 1797. Syn.: Acarus eruditus Schrank 1781. Anterior legs as long as body. Newstead and Duvall have shown that this species is parthenogenetic; they give the following particulars of the life-history and dimensions: Incubation period from 3 days in June to 15 in February. Pronymphal period from 5 to 17 days. Deutonymphal period from 7 to 20 days. Period between last ecdysis and first egg laid 13 to 17 days. 15 mm. long, I mm. broad, smooth. 23 mm. long after hatching to 32 mm. long 25 mm. (recent) to 39 mm. long (full fed). 54 to 57 mm. long (full fed). 69 to 71 mm. (recent) to 765 mm. long (full 66 1 Newstead and Duvall, Reports of the Grain Pests (War) Committee," No. 2, Royal Society. It is a common species in grain, cereals, hay, clover, and other feeding-stuffs, where it lives upon other soft-skinned forage-loving mites. It was very common FIG. 58.-CHEYLETUS ERUDITUS (AFTER NEWSTEAD AND MORRIS). X 325. Reproduced by permission from Report No. 8 of the Grain Pest (War) Committee of the Royal Society. in bales of hay and bran used in the British Expeditionary Force. I have examined specimens labelled Mark VIII., and taken from the horse's skin, which belonged to this species. It has been obtained from the ear of the guinea-pig,' and is stated to hunt Listrophorus gibbus (see p. 86) in the depths of the rabbit's fur. Picaglia2 blamed this form for causing a dermatosis of a horse. Megnin stated that he often found it upon horses, together with other acari which had tumbled from the rack. Newstead and Morris state that it has been found by them in groomings from healthy army horses in France and Flanders. I have seen veterinarians find this species in stable dust and blame it for causing a skin eruption for which they had failed to find the real cause-viz., the sarcopt. Genus Cheyletiella Canestrini 1886. Cheyletiella parasitivorax (Megnin 1878). This species differs from the last in that the palpi are not so large and have no combs on the last article but a bifid cirrus with three small hairs; the anterior two pairs of legs are shorter than the posterior; the tarsi end in a leaf-like cirrus with pectinate borders. Male 27 mm. long; female ·420 mm. long (Fig. 59). It does not produce disease, but is found in the depth of the rabbit's fur, where it is said to prey upon Listrophorus gibbus (see p. 85). I have detected it once in the dusty deposit from the skin of a cat which had strayed whilst severely affected with pneumonia. FAMILY TETRANYCHIDE Soft mites with trachea and two pairs of eyes; palpi composed of four segments, the last but one of which 1 Veterinary Journal, 1920, vol. lxxvi., p. 331. 2 Picaglia quoted by Railliet, Traité de Zoologie Médicale et Agricole, Paris, 1895, p. 696. has a powerful claw; the legs have six segments, with sucker discs between the claws of the tarsus. upon plants. Genus Tetranychus Dufour 1832. Parasitic Tetranychus molestissimus Weyenbergh 1886. "Bicho colorda " of the Argentine and Uruguay. It is found on the under-side of the leaves of South American plants, and from December to February attacks warm-blooded animals. Commonly called Red spiders. An allied species, T. telarius, causes "red disease " of the vine, and has been recorded from man in France. (See Fig. 60.) |