CHAPTER XXIV 

 PARASITIC INSECTS AND MITES 



Parasitic insects are common causes of skin diseases in 

 domestic animals. The diseased conditions of the skin, and the 

 irritation that they may cause the animal, depend on the life 

 history and habits of the parasite. Species that are unable to 

 live independently of a host and are permanent parasites are 

 usually the most injurious to the animal. This is especially 

 true of parasites that are capable of puncturing the skin or 

 burrowing into it. Temporary parasites may cause fatal forms 

 of disease. This is true of the larvae of the sheep bot-fly, which 

 develop in the sinuses of the head, causing severe inflammation 

 lof these parts, nervous symptoms and death. The character 

 of the symptoms of a parasitic disease depends on the habits 

 of the parasite, and the tissue or organ that it may attack. 



The parasitic flies belong to the order Dipt era, and the 

 families Muscidce and (Estridce. Fleas belong to the sub-order 

 Pulicidce. The order Herniptera includes the lice, and the 

 most important families are PedicuJidce and Ricinidce. Mites 

 and ticks belong to the order Acarina. The' most important 

 parasites belonging to this order are the SarcoptidcB and I.vodidw. 



CEstridae. — The three common bot-flies are the GastropJiilus 

 equi, Ilijpoderma lineata and (Estriis oris. These flies are 

 important because of the parasitic habits of their larvae. They 

 inhabit the stomach and intestines of horses (Fig. 62) ; the 

 subcutaneous tissue and skin of cattle ; and the sinuses of the 

 head and nasal cavities of sheep. 



The common hot-fiy of the horse {G. eqid) has a heavy, hairy 

 body. Its color is bro^^^l, with dark and yellowish spots. The 

 female fly can be seen during the warm weather, hovering around 

 the horse, and darting toward the animal for the purpose of 



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