THE WEB OF LIFE 311 



Some of the tales of parasites are grim, almost like 

 nightmare imaginings. Eoubaud has told us, for instance, of 

 two species of fly (he called the genus Choeromyia) which hve 

 in the burrows of the Cape Ant-Eater and the Wart-hog. 

 The adults Hve on dung and love darkness. The larvse 

 lie in the damp ground, able to endure prolonged fasting, 

 biding their time. They are attracted to the warmth of 

 their hosts ; they emerge from the earth and fix themselves 

 to the skin, piercing it and drawing blood. They can 

 ingest three times their weight of blood. Roubaud reared 

 one on himself, which reminds us that there is another 

 fly of somewhat similar habit, Auchmeromyia luteola, 

 whose larvae pierce the human skin and suck blood. 



Fabre tells us of a pigmy black Chalcid fly which follows 

 the giant Cigale, hke a Nemesis, as she lays her eggs in the 

 twigs. As soon as the Cigale has fllled one chamber and 

 passed on to the next, the anonymous Chalcid dehberately 

 inserts her alien egg, which eflectively undoes the larger 

 mother's labours. For out of the egg comes a grub which 

 devours the Cigale's eggs. ' A small, quick- hatching grub, 

 richly nourished on a dozen eggs, will replace the family 

 of the Cigale '. 



How curious, too, are the facts of hyper-parasitism, where 

 one parasite preys on another. The gall-fly Charips 

 victrix seems to destroy a beneficial Braconid that preys 

 upon plant-lice ; another gall-fly, Cothonaspis zig-zag, 

 destroys Phora aeletiw, which is a parasite of the injurious 

 cut-worm of the cotton. 



A comphcation in regard to the theory of galls has arisen 

 through the growth of scepticism as to the part which the 

 so-called gall-making animals play. Most galls are believed 

 to represent the plant's reaction to the secretions of the 



