414 INSECTS ABROAD. 



their peculiar fashion, so that they were as round as balls. 

 They are enabled to assume this attitude by means of the struc- 

 ture of the body. In the first place, the abdomen is attached 

 to the thorax by a short foot-stalk; and in the next, its under 

 .surface is hollowed. The insect, therefore, can bring the abdomen 

 completely forward, when the thorax and closed legs fit into the 

 hollow of the abdomen, and, the head being bent downwards, 

 the Ruby-tail is rolled up as completely as a hedgehog. 



There are numbers of species belonging to this splendid group, 

 and, on account of their insect-destroying habits, many of them 

 are extremely useful to agriculturists, as they feed not on the 

 food laid up for the larvae, but on the larva themselves. For 

 example, we have already seen that the larvae of certain Saw 

 Flies pass the chief part of their larval state upon the plant on 

 which the eggs have been laid, and then, when they are full-fed, 

 leave the plant and burrow into the ground, where they pass 

 through their changes into pupa and perfect insect. Such is 

 the case with the well-known Saw Fly which infests the goose- 

 berry; and the services rendered by the Chrysis in thinning 

 the numbers of these troublesome insects, are thus described 

 by M. St, Fargeau. 



He remarks that after the larva? of the Saw Fly had burrowed 

 into the ground, he saw a female Chrysis make its way to the 

 burrows, bend her abdomen forward, and thrust the tubular 

 ovipositor into the holes and deposit an egg in each, the whole 

 operation occupying barely a second of time. In the following 

 year he witnessed a wonderful sight at the same spot. At least 

 a hundred males as well as many females had been hatched, and 

 were traversing in all directions the ground in which the Saw 

 Fly larva had burrowed. As they ran backwards and forwards 

 in the sunbeams, their glittering bodies flashed like jewels, and 

 this beautiful scene was repeated for many clay-. 



The insects always made their appearance from ten to twelve 

 in the morning, after which time they dispersed; and M. St. 

 fargeau thinks that when they had once left the spot they did 

 not return, but that those which appeared on each successive 

 morning were merely hatched out of the cells of the Saw Flies 

 which they had supplanted. 



As is often the case with insects, the two sexes differ much in 

 their colouring, so that the males and females of the same species 



