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having the bristles erect, and others having them depressed. At first 

 sight I supposed that these bristles were a sexual character. 



I have shown at great length, in my Papers on Willow-gall In- 

 sects, published in the Proceedings of the Entomological Society ,of 

 Philadelphia, that, in the case of many larvae dwelling in the interior 

 of vegetable substances, and deriving their food from such substances, 

 there are what may be called "Guest-larvffi,"' belonging to distinct 

 Species, and often to distinct Genera, to distinct Families, and even 

 to distinct Orders of Insects. These last take advantage of the tene- 

 ment prepared for them by the original inhabitant, who thus becomes 

 their Host, and feed conjointly with him upon the same vegetable 

 food. Technically, such insects are called '"Inquilines ;*' but until I 

 publis>hed on the subject, entomologists were not aware how ex- 

 tensively this system prevails throughout the world of insects. From 

 the "Parasites," properly so called, these "Inquilines," or "Guests," as 

 we may call them in English, differ very widely, in that they are 

 normally vegetable feeders, and only occasionally or incidentally de- 

 stroy the life of their unfortunate Hosts; whereas the true "Para- 

 sites" feed exclusively upon the living bodies of their insect victims, 

 and with a few exceptions live inside those living bodies, devouring 

 the flesh piecemeal, although some few of them attach themselves ex- 

 ternally to their prey, and gradually suck its life away like so many 

 miniature leeches.* These last, by the way, must not be confounded 

 with what I have called "Cannibal" insects; for each of these exter- 

 nally-feeding Parasitical larva? attaches itself to a single victim, which 

 it never quits till it has attained its full growth, whereas the true Can- 

 nibal larva roams hither and thither, and before it attains its full 

 growth will probably have devoured dozens of victims. Hence, by a, 

 beautiful provision of nature, all the Parasitical larvae, whether in- 

 ternal or external feeders, are legless, because they have no occasion 

 for locomotion ; whereas all Cannibal larv^, inasmuch as they require 

 to move from place to place, are furnished with legs, and are usually 

 pretty strong on the leg besides. In two words — to return to our 

 new friends, the Guest-larvse — the difference between the Guest- 

 larvfe on the one hand and the Parasitical larva? and Cannibal larv?3 

 on the other hand, is pretty nearly that between an American burglar 

 on the one hand and a Polynesian cannibal on the other hand. The 

 insect Guest and the human burglar desire the goods of their victims 

 and do not usually take their lives, unless, for the object that they 



*1 have ascertained that a number of larvse belonging to the Chalcis fam- 

 ily have this peculiar habil , and antong the Ichneumon flies the genus Ophion 

 has long been known to feed externally in the larva state. 



