316 BIOLOGY: GENERAL AND MEDICAL 



buries herself beneath the skin of the host, 

 the abdomen then swelling to great size and 

 causing itching papules or " chiggerbuttons " 

 to form upon the skin. 



Order Coleoptera. Of these insects, the bee- 

 tles, a vast number are parasitic, in some 

 or all of their stages, upon plants, every imagin- 

 able structure being attacked by some kind of 

 beetle. 



Beetles are, however, very rarely parasites of 

 higher animals and rarely parasites of other 

 insects. An exception to this is found in the 

 interesting Stylopidae, which live between the 

 abdominal plates of certain hymenopterous 

 insects, the abdomen out of sight, the head 

 peeping out; another is found in Peatypsyllus 

 castris, which is an external parasite of the 

 beaver. 



Order Hymenoptera. This great order of in- 

 sects furnishes the greatest numbers and most 

 interesting examples of parasitism. In the 

 family Ichneumonidae more than ten thousand 

 parasitic species are already known, with acces- 

 sions constantly being made. 

 Some of the hymenoptera are plant parasites 

 and, like the dipterous insects of similar habits, 

 sting the plants at the time of oviposition in 

 such manner as to form galls and other excres- 

 cences, upon the tissue of which the larvae feed. 

 The usual habit of the hymenopterous parasites 

 is to ovulate in the larvae and pupae of other 

 insects, the eggs hatching in their bodies and 

 the larvae feeding upon the blood and fat until 

 ready to pupate themselves, when they usually 

 bore their way out and spin silken cocoons, in 

 which they mature. A familiar example of 

 such a hymenopterous parasite is found in 

 Apanteles congregatus, which tiny insect lays 



