"' Parasitic Insects. Hemijitera s. Rhynchota. 983 



cages with reeds into which the mites creep in the daytime, when 

 they can be destroyed. 



24. Insects Parasitic on the Domestic Animals. 



Of the class of insects belonging to the Hexapoda, several 

 species of the orders of Rhynchota, Hemiptera, Diptera, and 

 Aplianiptera as well as Hymenoptera are known to cause 

 more or less severe disease. Their injurious influence is exerted 

 in various ways. By creeping around on the surface of the skin 

 they irritate and hinder the animals from eating, especially on 

 pasture, and in weakly individuals this may now and then liave 

 serious consequences. Some insects nourish themselves on the 

 sweat or blood of their hosts, others inoculate acrid substances 

 into the skin or into the mucous membranes of the natural open- 

 ings of the body, causing acute edematous swellings, which 

 sometimes materially interfere with eating and breathing, but 

 at times produce severe general s5T:nptoms of poisoning. At the 

 bitten or stung spot deep seated changes may occur in the skin 

 or subcutaneous connective tissue, such as pustules, hemor- 

 rhages, abscesses, etc., which, on account of the itching usually 

 present, lead to traumatic artificial eczemas with the well known 

 results. The larvae of some varieties establish themselves on 

 raw surfaces, in the skin, and in the subcutaneous connective 

 tissue, or in the body cavities, occasion persistent and even se- 

 vere tissue changes, and in this way may cause the death of the 

 animals. Finally, certain varieties may bring al)out the spread 

 of infectious diseases by inoculating bacteria or protozoa adher- 

 ing to their bodies into the skin wounds. 



In the following pages these parasites will be discussed 

 briefly, while detailed descriptions will be left to zoological 

 works. 



A. Hemiptera s. Rhynchota. 



(a) Lice. (Pediculida.) Parasites generally occurring in 

 badly nourished or cachectic animals, the females of which glue 

 their pear-shaped eggs (nits) to the hairs. They suck blood, 

 cause itching and, when present in great number, lead to a 

 further decline in condition. They may multiply immensely, 

 especially in young cattle during the long stabling in winter, 

 from neglect of skin hygiene, and now and then cause extensive 

 eczema. In Germany lice occur more frequently in military 

 horses, especially in the eastern provinces where much oppor- 

 tunity for contagion from civilian horses is present (Wohler). 



In the domestic animals several varieties of blood sucking lice (Haematopinus) 

 occvir; thus in the horse Haematophinus s. Pediculus equi s. macroeephalus (Fig. 

 160), in cattle the H. eurysternus and the H. tenuirostris, in calves the H. vituli, 

 in goats the H. stenopsis, in dogs the H. piliferus, in pigs the H. suis s. urius. The 

 Hseniatopinus suis is the largest existing louse, its length reaching 4.5 mm.; very 



