388 PARASITES OF ANIMALS 



external parasites is the so-called horse-tick or forest-fly 

 (Hippobosca equina). They attack the abdomen, flanks, and 

 inner part of the thighs in great numbers, occasioning great 

 distress to the bearer. Being of leathery toughness their 

 bodies are not easily crushed, and they are removed only with 

 great difficulty. There is an equine disease in Sweden called 

 Staclcra, which is erroneously attributed to injuries produced by 

 a species of fly-maggot (Lixus) which lives on the fine-leaved 

 water-drop wort (Phellandrium) . As regards the so-called 

 free parasites, or rather non-parasitic obnoxious insects, which 

 torment solipeds, it is impossible even to enumerate them. 

 The tsetse of South Africa (Olossina morsitans) is terribly 

 fatal to the horse, but it is said that the mule, ass, and zebra 

 do not suffer from its bites an immunity shared by swine, 

 goats, antelopes, and man himself. Major Vardon's rash 

 experiment (based on the supposition that horses deprived of 

 fresh green food would not suffer from the attacks of the fly) 

 proved fatal to an animal which he purposely exposed* on a 

 much infested hill-top. The horse died ten days after it was 

 bitten. According to Chapman, the bites of four tsetse flies 

 are sufficient to kill an ox, but in man the irritation produced 

 is very slight. Amongst other insects proving troublesome to 

 solipeds may be mentioned the leg-sticker (Stomoxys calcitrans) , 

 the clegg (Hamatopota pluvialis) which is very abundant in the 

 West Highlands, various species of Tabanidae and Asilidce 

 (Tabanus autumnalis, T. bovinus, CJtrysops cacutiens, Asilus 

 crabroniformis) , and also a host of ordinary flies and gnats 

 (MuscidcB and Tipulida), as, for example, Anthomyia meteorica 

 and Culex equinus. In India the bite of a species of Simulia 

 gives rise to the formation of open sores of the most intractable 

 character. As regards hemipterous insects it may be said that 

 many species of lice (Anoplurd) produce what is called phthiriasis 

 or lousiness in the horse, some of them being derived from 

 poultry. The best known species are Trichodectes equi, T. 

 scalaris, Hcematopinus equi, H. vituli, H. eurysternus, and the 

 ass r louse (H. asini). Of the half dozen or more species infesting 

 the hen (belonging to the genera Goniocotes, Liotheum, &c.) 

 it is not probable that more than one or, at most, two of them 

 are concerned in the production of poultry-lousiness in the 

 horse. As an equine disorder this kind of phthiriasis was first 

 described by Bouley. Cases in England have been observed 

 by Messrs. Henderson, Moore, and Woodger. For some 



