THE SHEEP-LOUSE-PHTHIRIASIS-LOUSINESS. 

 Trichodectes sph^rocephalus, Nitzsch. 



Plate V. 



The little redheaded sheep-louse is not very abundant in this coun- 

 try, and easily escapes detection. It is, nevertheless, of sufiQcient 

 economic importance to engage our attention. 



The genus Trichodectes, to which this parasite belongs, is classed by 

 scientists in the order Mallophaga, to which order the bird-lice belong. 

 They are said by Packard [Guide lo Study of Insects, p. 554), to live 

 upon the hairs of mammalia and feathers of birds. 



Description. — The sheep-louse is quite small, about 1""" or one- 

 twenty- fifth of an inch in length. The female is slightly longer and 

 larger. It is characterized by its reddish head and the pale, transverse 

 bauds which cross the abdomen. Neumann describes the species as fol- 

 lows: 



Its head is wider thau loug ; truncated in front, the anteunal band making the 

 turn of the forehead which carries long hairs on its border. The autennie are hairy 

 and a little longer in the male than iu the female. The abdomen carries sub-quad- 

 raugiilar median spots. The general color is whitish ; the spots and head are ferru- 

 ginous. Length of female 1.6""", and male 1.4™™. 



This general descrii)tion is very good, but would hardly serve to dif- 

 ferentiate this species from others without figures and comparative 

 descriptions. Entomological anatomists enter into very minute details 

 of description for determining these species, but a comparison of speci- 

 mens found with the figures in Plates V and VI will assist the farmer 

 more thau a loug technical description. As yet the only form recorded 

 from sheep in this country is the one species, Trichodectes sphwrocepha- 

 lus, or T. ovis, which is a synonym. The following appear to be the 

 most marked differences between this and other species : The species is 

 generally smaller than others. The breadth of the abdomen is relatively 

 narrower, and that of the male seems to be more obtuse. The dorsal 

 sutures on the head (see Plate V, Fig. 2 e, e), are fainter iu the middle. 

 The -front of the head is more convex. The brown markings on the 

 head are all relatively fainter; those on the back of the male and 

 female increase from the first to the fourth and then decrease to the last 

 iu a gradual manner. The claws of both anterior and posterior feet are 

 more nearly of the same size. The eggs (Figs. 6 and 7) are midway in 

 size between those of the two species figured on Plate VI. These eggs 

 have a cap marked by vertical stride, which constitute a generic charac- 



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