222 FLEAS, FLUKES AND CUCKOOS 



One of the most interesting flies parasitising birds is Camus hemap- 

 terus. It is a tiny, shining, black-bodied fly, only a few millimetres in 

 length and it lives among the feathers of the host. The life-cycle is 

 passed in the nest. The larva (according to Nordberg) is saprophagous 

 and feeds on dead and decaying animal matter. Up to a few years ago 

 it was thought that the adult was a blood-sucker, but the mouth-parts 

 are not adapted for piercing and sucking and it is now considered more 

 probable that it feeds on the fatty or waxy exudates from growing 

 feathers. Both sexes of the fly are fully winged when they hatch, but 

 after reaching a host — even if the distance covered is a few inches from 

 the bottom of the nest to the back of a nestling — they break off their own 

 wings, some distance from the base where there is a line of weakness, 

 leaving a stump. After the wings are shed the abdomen becomes 

 enormously distended owing to the abnormal growth of the fatty tissues. 

 This curious condition is known as physogastry and it is usually devel- 

 oped by flies and beetles which are parasitic or symbiotic in ants' or 

 termites'nests. 



Camus hemaptems has a wide distribution in Europe and America. 

 Host-selection seems to depend on the type of nesting site rather than 

 the species of bird. Tits, starlings, woodpeckers, and other hole-nesters are 

 greatly favoured, but a wide range of host records exists which includes 

 falcons, finches, warblers, crows, pigeons and swallows. It is not a com- 

 mon species in this country, although it is probably often overlooked, 

 and has been bred from the nests of the starling, hedge-sparrow, barn- 

 owl and blackbird. There are numbers of British species from the allied 

 genus Meoneura, all of which are very small flies about one mm. in 

 length. Sand-martins appear to be the host of M. lamellata, and a great 

 variety of birds harbour M. neottiophila in their nests, including hawks, 

 tits, woodpeckers, pigeons, finches, blackbirds, and carrion-crows. 



The bird itself is an important enemy of flies but the various para- 

 sites which attack them are more important, especially in the larval 

 stages. One type of mite eats the eggs of Muscidae, the adults hitch- 

 hiking around on the body of the fly. There is also a formidable list of 

 Protozoa (including the trypanosomes) and Fungi, of which flies are the 

 known host. An exceptionally large number of pathological organisms 

 are associated with Diptera owing to their unsavoury habits. Thus 

 while feeding upon the excrement of birds they swallow the spores of 

 Coccidia, the causative agent of so-called grouse disease, which is thus 

 spread to other individual birds. They also swallow the eggs of tape- 



