84 SCIENTIFIC ILLUSTRATIONS [Dea 



Destruction of Destroyers. 



The green and black caterpillars of the white cabbage 

 butterfly, devastate our cabbage beds, make sieves of the leaves, 

 and are disagreeably tenacious of their rights of possession. 

 Pest as it is to the gardeners and cooks, it would be a hundred- 

 fold worse but for the exertions of a fly so small as hardly to be 

 noticed but by its effects. Small though it be, one such insect 

 can compass the destruction of many a caterpillar, though not 

 one thousandth part of the size of a single victim. While the 

 caterpillar is feeding, the ichneumon fly, as it is called, settles 

 upon its back, pierces its skin with a little drill wherewith it 

 is furnished, and in the wound deposits an egg. This process 

 is repeated until the ichneumon's work is done. As each 

 wound is made the caterpillar seems to wince, but shows no 

 further sense of uneasiness and proceeds with its eating as 

 usual. But its food serves very little for its own nourishment, 

 because the ichneumon's eggs are speedily hatched into ichneu- 

 mon grubs, and consume the fatty portions of the caterpillar as 

 fast as it is formed. In process of time the caterpillar ought to 

 take the chrysalis shape, and for that purpose leaves its food 

 and seeks a convenient spot for its change. That change never 

 comes, for the ichneumons have been growing as fast as the 

 caterpillar, with whose development they keep pace. And no 

 sooner has their victim ceased to feed, than they simultaneously 

 eat their way out of the doomed creature, and immediately 

 spin for themselves a number of bright yellow cocoons, among 

 which the dying caterpillar is hopelessly fixed. Sometimes it 

 has sufficient strength to escape, but it never survives. co. 



Detection of Destroyers. 



When the caterpillars of the buff-tip moth have increased to 

 a tolerably large size, they disband their forces, and each indi- 

 vidual proceeds on its own course of destruction. Were it not 

 for the colours they assume, these creatures would do great 

 damage ; but the ground being yellow and the stripes black, the 

 caterpillars are so conspicuous that sharp-sighted birds soon find 

 them out, and having discovered a colonyj hold revelry thereon, 

 and exterminate the band. co. 



