118 WORK AT HOME AND IN THE FIELD 



insect patients with very great success ; but we must do our best 

 to adopt hygienic principles, paying the greatest attention to 

 proper means of ventilation and to a regular and wholesome diet- 

 ing. In the case of diarrhoea a very common insect malady the 

 best we can do is to avoid the young and juicy leaves of the food 

 plant, and substitute the older and drier foliage. 



Ichneumon flies have already been mentioned as great enemies 

 of larvae. These flies either deposit their eggs on the skins of 

 caterpillars, or thrust their sharp ovipositors into the creature's 

 flesh and lay their eggs beneath the skin. When the young 

 ichneumons are hatched, they immediately begin to feed on the 

 fatty matter that is usually stored in comparative abundance under 

 the skin of the caterpillar, and thus they grow at the expense of 

 their host, within whose body they lie completely hidden from 

 view. 



The poor caterpillar, though being eaten alive, often shows no 

 external signs of the mischief wrought within, and, even though 

 its substance is really decreased by the hungry internal parasites, 

 yet the rapid growth of these robbers maintains the general plump- 

 ness of a healthy larva. But the ichneumons, having at last 

 devoured the store of fat, and avoided the vital organs of the 

 caterpillar, as if with a view to preserve their living home to the 

 latest moment, now commence to attack the latter, speedily 

 reducing the vitality of their host to the lowest ebb, and finally 

 causing its death. 



This untimely end may come before the caterpillar is full grown, 

 or the insect may change to the pupa before the ichneumons have 

 done their worst, but it rarely occurs that the unfortunate creature 

 has sufficient strength to carry it on to the final stage. 



A large number of the collected larvae will have been ' stung,' 

 much to the disgust and disappointment of the rearer ; and hence 

 the advantage of rearing your specimens from ova wherever possible, 

 providing you keep them so well under cover that the ichneumons 

 cannot visit your broods. 



The Management of Pupce 



The disappointments connected with the rearing of Lepidopteni 

 are by no means at an end when all have passed successfully into 

 the pupal condition, and the number of perfect insects obtained 

 will often fall far short of the number of pupae in your boxes ; but 



