y2 FLEAS, FLUKES AND CUCKOOS 



in used spittoons. Aristotle was quite ignorant of the life-history of the 

 flea but he had observed that dung was a contributing factor to their 

 welfare. He wrote, "Fleas are the result of putrefaction of smaller 

 bodies, for example where dried dung is, there you find fleas." One 

 early naturalist reared the larvae on "the bran hke substance which 

 sticks in the comb when puppies are combed." It appears that this 

 unattractive diet is adequate for the larvae of the tropical rat flea and the 

 human flea but not for all species. Sharif proved that in addition to organic 

 refuse which forms a necessary part of its diet it is essential for the larvae 

 of the common rat flea to eat small quantities of blood. In nature this 

 is provided by the female flea which, during her interminable meals, 

 squirts out quantities of undigested blood through the anus, and thus 

 amply justifies her Gargantuan appetite. 



It was also proved experimentally that it is impossible to rear 

 larvae successfully if the iron content has been extracted from the blood 

 fed to them. One wonders if, in some cases, the blood-sucking habit of 

 insects was acquired in connection with a lack of iron in their diet. 

 This substance is essential to their normal growth and development, 

 and a new source of supply may have conferred an immeasurable 

 advantage on the pioneers who first tapped it accidentally. 



It is, however, most unusual for an insect to require blood during 

 more than one phase of its life-cycle and in this way, as in so many 

 others, fleas are peculiar and exceptionally interesting. " Her young 

 ones also suck up blood." In the case of the common house-martin flea 

 [Ceratophyllus hirundinis) and the common hen flea it is known that their 

 larvae thrive best on food which contains excrement and blood drop- 

 pings of their parents, but it appears that at a pinch they can be reared 

 successfully on broken down feather sheaths and epidermal scales. 



The larvae of fleas sometimes swarm in thousands in one nest. 

 It is therefore not surprising that they are occasionally found on the 

 bodies of nesthngs. Twenty per cent, of sand-martins are said to be 

 infested during the nesting season. No doubt if they could evolve a 

 closer relationship with the host at the larval stage their lives would be 

 less hazardous and bird fleas as a whole might, Hke the feather Hce, 

 become more successful in the walk of life they have chosen. 



The larva spins itself a cocoon before pupating. This is attached to 

 twigs in the nest, and since grains of sand and dirt adhere to the outside, 

 the camouflage is most efl^ective. There is a certain amount of specific 

 variation in the structure of cocoons. Those of the common hen flea 



