INSECTS IN RELATION TO OTHER ANIMALS 277 



inoculating them with a protozoan blood-parasite, to the effects 

 of which, fortunately, man is not susceptible. 



Parasitic Insects. Insects belonging to several diverse 

 orders have become peculiarly modified to exist as parasites 

 either upon or within the bodies of birds or mammals. 



Almost all birds are infested by Mallophaga, or bird lice, of 

 which Kellogg has catalogued 264 species from 257 species of 

 North American birds. Sometimes a species of Mallophaga is 

 restricted to a single species of bird, though in the majority of 

 cases this is not so. Several mallophagan species often infest 

 a single bird; thus nine species occur on the hen, and no less 

 than twelve species, representing five genera, on the American 

 coot. These parasites spread by contact from male to female, 

 from old to young, and from one bird to another when the 

 birds are gregarious. When a single species of bird louse 

 occurs on two or more hosts, these are almost always closely 

 allied, and Kellogg has suggested the interesting possibility 

 that such a species has persisted unchanged from a host which 

 was the common ancestor of the two or more present hosts. 

 Mallophaga are not altogether limited to birds, however, for 

 they may be found on cattle, horses, cats, dogs, and some other 

 mammals; Kellogg records eighteen species from fifteen 

 species of mammals. These biting lice feed, not upon blood, 

 but upon epidermal cells and portions of feathers or hairs. 

 They have flat tough bodies (Fig. 17), with no traces of wings, 

 and a large head with only simple eyes ; the eggs are glued to 

 feathers or hairs. 



Mammals only are infested by the sucking lice, or Pediculidae 

 (Hemiptera). These (Fig. 23) have a large oval or rounded 

 abdomen, no wings, a small head, minute simple eyes or none, 

 and claws that are adapted to clutch hairs ; the eggs are glued 

 to hairs. Sucking lice affect horses, cattle, sheep, dogs, mon- 

 keys, seals, elephants, etc., and man is parasitized by three 

 species, namely, the head louse (Pediculus capitis), the body 

 louse (Pediculus vestimenti), and the crab louse (Phthirius 

 pubis), though the first two are possibly the same species. 



