Cocoons, Nests and Eggs 



Certain insects' eggs cannot hatch without the aid of 

 some higher animal, aid which is certainly involuntary, 

 seeing that the larvae from these eggs are parasitic. Let 

 us consider two totally dissimilar cases. There is a British 

 fly, not unlike a honey-bee in appearance and known as 

 the horse bot-fly. This insect is an interesting though 

 obnoxious pest to horses, in whose neighbourhood it may 

 often be seen flying on warm sunny days. Suddenly the 

 fly will dart at a horse, settle for an instant and fly away 

 rapidly. This operation will be repeated over and over 

 again. Each time the fly settles on the horse she deposits 

 a single elongated egg which is so sticky at one end that 

 it becomes attached to a single hair of its host. The eggs 

 are always attached on some part of the horse which may 

 easily be reached by its tongue, for a reason we shall see 

 presently. The free end that is, the unattached end of 

 each egg is furnished with a little lid. Now the presence 

 of these eggs irritates the horse. What then is more natural 

 than that it should lick the offending spot ? And this is 

 precisely what the mother fly intended should happen. 

 The friction of the animal's tongue in conjunction with 

 its saliva causes the little lids of the eggs to open, and out 

 come the larvae. They pass into the horse's mouth, thence 

 to its stomach, and affix themselves to its wall. But that is 

 another story. Let us turn to our second example, which 

 is even more curious. 



A South American fly, or rather its grub, lives in the 

 flesh of human beings, causing ugly, suppurating tumours. 

 How these grubs entered the flesh of their hosts long 

 remained a mystery, till a French naturalist solved the 

 riddle. The fly had never been seen to lay its eggs on 

 a human being or on his clothing, yet its grubs certainly 

 made a home in his flesh. How came they there ? The 

 capture of a blood-thirsty, blood-sucking mosquito, with 

 some of the eggs of this obnoxious fly adhering to its 

 abdomen, gave a clue to the mystery. Piece by piece the 

 evidence was constructed, till at length the problem was 



