218 INJUKIOUS IKSECTS 



stupidity, or disappointment, nips off the stalks of the 

 half-grown grapes and allows them to fall to the ground 

 untasted. It is fortunate for the grape-grower therefore 

 that Nature has furnished the ready means to prevent its 

 ever becoming excessively numerous, for we have never 

 known it to swarm in very great numbers. The obvious 

 reason is, that it is so freely attacked by a small parasitic 

 Ichneumon-fly belonging to a genus (Microgaster) ex- 

 ceedingly numerous in species that three out of every 

 four worms we meet with will generally be found to be 

 thus victimized. The eggs of the parasite are deposited 

 within the body of the worm, while it is yet young, and 

 the young maggots hatching from them feed on the fatty 

 parts of their victim. After the last moult of a worm 

 that has been thus attacked, numerous little heads may 

 be seen gradually pushing through different parts of its 

 body; and as soon as they have worked themselves so far 

 out that they are held only by the last joint of the body, 

 they commence forming their small snow-white cocoons, 

 which stand on end, pushes open a little lid which it had 

 previously cut with its jaws, and soars away to fulfil its 

 mission. It is one of those remarkable and not easily 

 explained facts, which often confront the student of Na- 

 ture, that, while one of these Hog-caterpillars in its nor- 

 mal and healthy condition may be starved to death in 

 two or three days, another that is writhing with its 

 body full of parasites will live without food for as 

 many weeks. Indeed we have known one to rest for 

 three weeks without food in a semi-paralyzed condition, 

 and after the parasitic flies had all escaped from their 

 cocoons, it would rouse itself and make a desperate 

 effort to regain strength by nibbling at a leaf which 

 was offered to it. But all worms thus attacked suc- 

 cumb in the end, and the grape-grower should let 

 alone all such as are found to be covered with white 

 cocoons, and not, as has been often done, destroy them 



