1869.] RITCHIE — ON PIERIS RAP^. 299 



other animals, have their peculiar parasite, and, in the majority 

 of cases, are preyed upon by those creatures internally and 

 externally. The most beneficial parasites to us, in connection 

 with insect pests, are the ichneumons. 



One of the reasons that Pieris Ripoe does not commit such 

 ravages in England, is, no doubt, owing to the fact — one well 

 attested by Entomologists — of the powerful check kept on this 

 species in Europe by ichneumons. 



Reaumur writes as follows : — " Out of thirty individuals of 

 this common cabbage caterpillar, put into a glass to feed, twenty- 

 five were fatally pierced by an ichneumon (Micwgaster glohatus)." 

 Such a percentage of mortality must tell on a colony of cater- 

 pillars. 



The question may here be asked, after the recommendation of 

 hand-picking, netting, &c., is nature doing anything to help us 

 in the matter of the cabbage butterfly in Canada ? We 

 answer in the affirmative. Any observer of the larvae on 

 cabbages will have noticed a small four-winged fly very actively 

 running over the plants, looking as if it had lost something, 

 running down this rib, then up that, under one leaf, then flying 

 to another. By close attention you will see the cause of this 

 uneasiness on the part of this little hi/menopter, for so we call 

 her, as she belongs to the Hymenoptera, or membranous winged 

 order of insects. She.i§ hunting the caterpillars of the cabbage 

 butterfly, for the purpose of dvipositing her egg or eggs in their 

 bodies. This she does by means of her ovipositor, piercing the 

 body of the creature — but not in a vital part — so that her young 

 may have a nidus where food will greet them immediately on 

 their comjng out of the egg. They then live on the juices 

 of the caterpillar until they (the parasites) undergo their 

 metamorphosis and attain the imago or winged state, when they 

 eat their way out of the caterpillars' bodies and fly away. This 

 is given as an illustration of one of Nature's methods of keeping 

 in check noxious caterpillars. We noticed this circumstance 

 last summer in connection with the cabbage butterfly. In all 

 probability the preponderance of ichneumons will so afi'ect the 

 prospects of this insect that in a year or two they will become 

 good colonists, and instead of producing want and famine they 

 will ornament our Canadian landscape by their airy gambols 

 and spare the cabbages. 



Still farmers and gardeners should not leave all to nature, but 



