FLEAS 91 



prevalent group of fleas on rats and mice on the mainland of North 

 Africa. Similarly penguins and certain other sea birds nesting on the 

 islands off South America, South Africa and Australia and on various 

 islands in between such as Bird Island, the Falkland Isles, Kidney Isle 

 and so forth, are infested with a genus of fleas clearly descended from 

 South American rodent fleas. Originally they must have picked up 

 these fleas in the Cape Horn area and carried them westwards and 

 eastwards to their various breeding stations. On the Kerguelen Isles, 

 in South Georgia and on Antipodes Isle, the diving petrel {Pelecanoides 

 urinatrix), a gull {Larus dominicanus) and a burrow-nesting parrakeet 

 [Plaiycercus unicolor) have each acquired a flea of the family Pygiop- 

 syllidae, a group of primitive marsupial fleas which are the dominant 

 Aphaniptera of the Australian region. 



In Britain we have 16 species of bird fleas. Of these no less than 1 1 

 belong to the genus Ceratophyllus, The family in which these fleas are 

 placed contains the majority of species from the north temperate 

 climates of the world, and the genus in question claims 45 out of some 

 55 bird fleas known. These fleas have made the change over to birds 

 along a slightly different evolutionary path from those mentioned 

 above. They are clearly descended from the fleas of tree-climbing 

 rodents such as squirrels and certain rats (Plate Xld), and have 

 probably been evolved from this source twice or even more often. Both 

 types of hosts have developed arboreal habits, and the fleas from 

 squirrels are in a sense pre-adapted to the dry aerial environment of 

 birds' nests. The mutual arboreal habit now ensures the necessary 

 opportunity for straggling. Ceratophyllus gallinae has been recorded 

 frequently from squirrels' dreys and the squirrel flea [Monopsyllus 

 sciurorum) is repeatedly found in birds' nests. It has been collected from 

 crows' nests in Northamptonshire in localities where the rightful host, 

 the red squirrel, is no longer to be found. 



There are two other genera of bird fleas represented in Britain 

 which, although they may be included in the same family, are not 

 closely related to Ceratophyllus. The first is Dasypsyllus gallinulae, a flea 

 found on a wide variety of birds nesting on or near the ground. This is 

 rather an ancient and obscure genus and it is only possible to hazard 

 a guess as to the mammal fleas from which it is derived. The arrange- 

 ment of bristles on the head is somewhat similar to that found on a 

 prevalent genus of South American fleas, Pleochaetis, which may have 

 given rise to Dasypsyllus. All the other known species, except one, are 



