FLEAS 71 



hen stick-tight flea dies in the larval stages if the temperature falls 

 below 50°F. Our poultry is thus saved in this country from a serious 

 scourge. 



The flea larvae rip up the egg shell, which generally cracks longitu- 

 dinally, with a spine situated on the front of the head. When they 

 emerge after about ten minutes' wriggling they are minute cylindrical 

 semi-transparent maggots adorned with a few hairs but without eyes 

 and with merely a pair of anal struts on the last segment to serve as 

 appendages (Plate XVIII). Some species are very much more hairy 

 than others. They twist about actively in the nest debris and some- 

 times curl themselves up sharply like a watch spring. It is especially in 

 this stage that fleas require a humid atmosphere. Even the sweat and 

 urine from the host's body play a large part in keeping the larvae 

 alive. They cannot survive dry heat. Feather lice which pass their 

 early stages on their hosts are independent of external climatic changes 

 and their situation in this respect is singularly secure compared with fleas. 



Buxton once measured the relative temperature and humidity in a 

 Palestine cow-shed and two rat holes opening into it. The temperature 

 recorded was the same in all three spots, but the greater humidity in 

 the holes was sufficient to make the development of the flea larvae 

 possible within them. No doubt it is the moisture requirements of the 

 larvae which has imposed one of the greatest barriers to the infestation 

 of birds by fleas. For insects such as these the change from a mammal's 

 humid nest or lair to the dry aerial home of birds is revolutionary. It is 

 significant that most of the existing bird fleas are found on species which 

 breed on the ground and in banks, or use mud freely in the construction 

 of their nests. 



According to the temperature and humidity, which may speed up 

 or delay metamorphosis during all its phases, the larval stage of a flea 

 may last from one to twenty-four weeks. During this period it moults 

 three times. (There are a few exceptions among the sedentary species 

 which have only two moults.) 



It is an undisputed fact that the mouth-parts of the larvae of fleas 

 are adapted to gnawing but their diet has been the source of endless 

 discussion. Leeuwenhoek as far back as 1694 noticed larvae of the 

 pigeon flea "red with blood" but subsequent writers maintained that 

 this element did not form part of their normal food. On the contrary, 

 they were said to maintain themselves on organic refuse such as the 

 dung of their host, dead flies, the bodies of adult fleas and the sawdust 



