Parasites and Predators 



couple of eggs in each parasitised egg. From the hyper- 

 parasite's eggs two fat and lusty grubs emerged, and they 

 remained within the gipsy-moth's egg, feeding upon the 

 yolk. Fate, however, was not to treat them kindly, for 

 they had hardly begun to enjoy life when a third parasite 

 came along and deposited its egg within that of the gipsy- 

 moth. From the egg of this third parasite there hatched 

 a youngster, which devoured his two companions, the 

 grubs of the second parasite and, weathering all the 

 storms of infancy, emerged in due course as a perfect 

 insect. 



And the tale with variations could be repeated over and 

 over again. The struggle for existence amongst the insects 

 is indeed severe. Amongst the birds, parasites are not 

 common, or we should say, more correctly, that bird 

 parasites are not common, for the birds, like the rest of us, 

 have their worries in the shape of insect parasites. Many 

 of the cuckoos have parasitic tendencies ; the frigate-birds 

 and skuas are also parasites. 



A most peculiar and insidious parasite, known as 

 Sacculina^ occurs amongst the crabs. Sacculina in its 

 young stages is a free swimming individual ; with the 

 passage of time it loses its good character, enters the body 

 of a crab and resigns itself to a parasitic life in its worst 

 form. Changing its appearance as well as its habits, it 

 becomes converted into what may be termed as little 

 better than a growth which branches in all directions 

 within the body of its unfortunate host. 



The worms can offer parasites galore, unpleasant 

 creatures most of them, yet teeming with interest one and 

 all. Flat-worms, tape-worms, thread-worms and liver- 

 flukes, they are nearly all of parasitic habit. We may let 

 the very common liver-fluke serve as our example of 

 a parasitic worm. This creature lives upon the livers of 

 sheep and cattle. They are not pleasant visitors, for they 

 cause the death of hundreds of thousands of sheep 

 annually. They are interesting because they form an 



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