220 ENTOMOLOGY. 



undergoes in Europe an extraordinarily rapid growth; it 

 stings early in June the chrysalids of Vanessa poly chloros, 

 and by the middle of July the adults appear. I'cleas ovu- 

 lorum requires only from four to six weeks to develop; it, 

 however, flies somewhat later, so as to find the young silk 

 caterpillars on which to lay its eggs. 



Ichneumons rarely develop within adult insects, but cer- 

 tain Braconids infest Coccinellae. The small Ohalcids 

 (Pteromali) mostly inhabit the tender pupae of bark-boring 

 beetles and leaf-rollers. Among the smaller ichneumons 

 several females usually inhabit a single host, while from GOO 

 to 700 individuals of Pteromalus puparum may inhabit a 

 single chrysalid. 



Most, ichneumons develop within their hosts, but many 

 species of Chalcids live on the outside and suck the blood 

 of their victims. Certain ichneumon larva; living within 

 their host undergo the most remarkable change as respects 

 their mouth-parts. In the larva of Microgaster globatus 

 (according to Judeich and Nitsche) there are in the early 

 stages only the wart-like rudimentary sucking mouth-parts, 

 but after the last moult they acquire ordinary biting mandi- 

 bles, with which they can gnaw through the skin of their 

 host. 



The yonng of the Tachina-flies are true footless maggots, 

 and take their liquid food by suction through the mouth, 

 the mouth-parts being very rudimentary. Tachina (Seno- 

 metopia) militaris has been observed by Riley to lay from 

 one to six eggs on the skin of the army-worm, "fastening 

 them by an insoluble cement on the upper surface of the 

 two or three first rings of the body." The young maggots 

 on hatching penetrate within the body of the caterpillar, 

 aud, lying among the internal organs, absorb the blood of 

 their unwilliug host, causing it to finally weaken and die. 

 Usually but a single maggot lives in its host. Many grass- 

 hoppers as well as caterpillars are destroyed by them. 



Insectivorous Insects. — There are very many carnivorous 

 kinds which devour insects entire. Such are the ground- 



