278 ENTOMOLOGY 



An anomalous beetle, Platypsyllus castoris, occurs through- 

 out North America and also in Europe as a parasite of the 

 beaver. 



The fleas, allied to Diptera but constituting a distinct order 

 (Siphonaptera), are familiar parasites of chickens, cats, dogs 

 and human beings. These insects (Fig. 30) are well adapted 

 by their laterally compressed bodies for slipping about among 

 hairs, and their saltatory powers and general elusiveness are 

 well known. Their wings are reduced to mere rudiments, their 

 eyes when present are minute and simple and their mouth 

 parts are suctorial. 



Among Diptera, there are a few external parasites, the best 

 known of which is th sheep tick (Melophagus ovinus) , though 

 several highly interesting but little-studied forms are parasitic 

 upon birds and bats. 



The larvae of the bot flies (CEstridse) are common internal 

 parasites of mammals. The sheep bot fly (CEstrus ovis) 

 deposits her eggs or larvae on the nostrils of sheep; the 

 maggots develop in the frontal sinuses of the host, causing 

 vertigo or even death, and when full grown escape through 

 the nostrils and pupate in the soil. The horse bot fly (Gas- 

 trophilus equi) glues its eggs to the hairs of horses, especially 

 on the fore legs and shoulders, whence the larvae are licked off 

 and swallowed; once in the stomach, the bots fasten them- 

 selves to its lining, by means of special hooks, and withstand 

 almost all efforts to dislodge them ; though when the bots have 

 attained their growth they release their hold and pass with the 

 excrement to the soil. Bots of the genus Hypoderma form 

 tumors on cattle and other mammals, domesticated or wild. 

 The ox-warble (H. lineata, Fig. 210, /) reaches the oesophagus 

 of its host in the same manner as the horse bot, according to 

 Curtice, but then makes its way into the subcutaneous tissue 

 and causes the well-known tumors on the back of the animal ; 

 when full grown the bots squirm out of these tumors and drop 

 to the ground, leaving permanent holes in the hide. 



Parasitism in General. Parasitic insects evidently do not 



