56 CHILDHOOD OF ANIMALS 



surface, usually creeping out on the banks. The larval integument 

 then splits open and a creature which has the form of a winged 

 insect and seems able to fly emerges. This, however, goes through 

 another moult, generally within a few minutes or hours of the first 

 moult, and the perfect insect appears and takes to flight. Its 

 mouth-organs are rudimentary and it is incapable of taking food, 

 and dies generally three or four hours after its emergence, in this 

 brief space of time having met the other sex and performed the 

 duties of reproduction. Dragon-flies similarly lay their eggs in 

 water ; the larvae live from one to two years, and then, coming to 

 the surface, go through metamorphosis. The perfect insects are 

 predaceous creatures with powerful jaws ; they hawk and devour 

 smaller insects, but the total duration of their adult life is at most 

 a few months. In many beetles the disproportion between the 

 duration of youth and of the adult is still more remarkable. The 

 larvae of longicorn beetles are vegetarian, burrowing in the bark or 

 wood of-trees. Mr. C. J. Gahan has related a remarkable case under 

 his own observation. In May 1890 Captain Ernest Blunt, R.E., 

 brought one of these larvae to theBritish Museum. The larva was in a 

 boot-tree which he had had in use for fourteen years, seven of which 

 had been spent in North -West India. The larva was transferred 

 to a piece of beech-wood forming part of a museum stand, and lived 

 there until May 1895, when it was transferred to a fresh piece of 

 wood ; it died shortly afterwards. Mr. Gahan has told me of 

 another case. Mr. Walter Rose, of Ilford, sent to the Museum in 

 September 1910 the wooden base of a bronze ornament which he 

 had had for just five years. It was one of a pair given him, but he 

 was unable to find out where it had come from. Two longicorn 

 beetles of a South European species emerged from the wooden 

 base a day or two after it had been received at the Museum. That 

 gave five years certain with some unknown period in addition for 

 the life of the larvae. The exact duration of the life of the adults 

 is not known, but certainly is very much shorter than that of the 

 larvae, usually not extending over the first winter after emergence. 

 A still more extraordinary case is that of the seventeen-year cicada, 

 a North American land bug. The adult insects are heavily built 

 creatures nearly an inch and a quarter in length, with two pairs of 

 transparent wings. The mouth -parts are imperfect and the creatures 

 do not feed, living only two or three weeks. The eggs are laid in 

 slits cut in the bark of trees, and the larvae, soon after hatching, 

 burrow into the ground, where they live on vegetable matter. They 



