1 1 6 Book-lice and Bark-lice ; Biting Bird-lice 



The most interesting thing in connection with the Mallophaga, excepting 

 their parasitic life and strange food-habits, is the puzzling problem of their 

 distribution. The problem in its largest phase is this: the species of Mal- 

 lophaga are, in a majority of cases, peculiar (so far as recorded) each to some 

 one host species. But the instances are many where a single parasite species 

 is common to a few or even to many host species. How does this condition 

 of commonness to several hosts come to exist? 



As the Mallophaga are wingless, their power of migration from bird to 

 bird is limited. Moreover, they can live for but a short time off the body 



of a warm-blooded host. After a bird is 

 shot, the Mallophaga on it die in from 

 two hours to three or four days: in rare 

 cases living individuals are found on the 

 drying bird-skin after a week. Although 

 the parasites in a badly infested hen-house 

 will be seen on the roosts and in the nests, 

 in Nature the insects are rarely found off 

 the host's body. On such a likely place 

 as an ocean rock from which I had just 

 frightened hundreds of perching pelicans, 

 cormorants, and gulls no parasites could 

 be found. Practically migration must be 



accomplished while the bodies of the hosts 



FlG. 145. Bonnet-shaped pharyngeal mntart c 1]r u rac , pc . 



ar( ' ntact ' 



sclerite, lateral aspect, from a biting 



bird-louse, Eurymo$tus taurus, from mating and nesting, and when gregarious 



an albatross. (Greatly magnified.) b j rds roost Qr perch dosely together- 



Occasional migration might occur from a bird of prey to its captured 

 victim, or from victim to hawk. 



The general character of the cases in which a single Mallophagan species 

 is common to several host-species may now be considered. Docophonis 

 lari has been found on thirteen species of sea-gulls, and Nirmus lineolatus 

 on nine. Gulls are gregarious, perching together on large food-masses 

 and on ocean rocks. But on these rocks gulls are closely associated with 

 other coast birds, as cormorants, pelicans, murres, etc. And the gull-para- 

 sites might have opportunities to migrate to these other bird-species. 

 Docophorus icterodes and Trinoton luridum are common to many duck species 

 (each has been collected from nine), but ducks also are gregarious, and in 

 addition are much given to hybridizing. But a parasite may be common to 

 several host-species of non-gregarious habits. Docophorus platystomus is 

 common to several hawk-species, D. cursor to several owl-species, D. excisus 

 to several swallows, D. californiensis to several woodpeckers, and D. com- 

 munis to several passerine birds. In the other genera of Mallophaga are 



