46 OUTLINES OF ENTOMOLOGY. 



punctured and a great number of the little grub-like larvae hatch and 

 burrow back and forth in the fatty tissue of their victim, avoiding at 

 first its vital parts ; and when it is fatally injured, though perhaps it 

 [Fig. 20.] does not die for several days, they emerge in an 



erect position and cover the back of the cater- 

 pillar with their email white cocoons attached 

 r^w'thVcoonsol ** tbe lower end and standing up like grains of 



pastes (after Riley). Color, ^ flU Qver j t M()gt of the largef gpecies 



weave their cocoons inside the body of their victim. The internal 

 parasitic larvae are said to breathe through branchia similar to those of 

 water insects, which are situated at one end of the body and communi- 

 cate with the air tubes of the insect they infest. 



The large species represented in Fig. 19 is Opihon Macrurum, Linn. 

 The abdomen broadens toward the tip and is compressed laterally. 

 The entire body and wing- veins are of a honey-yellow color. It quite 

 frequently enters our lighted rooms on summer nights, and if taken 

 into the hand will administer so sharp a thrust with its ovipositor that 

 the captor involuntarily releases it. It is parasitic on the large cater- 

 pillars belonging to the family of our native silk worms. 



The PBOCTROTRYPID^S is a family of exceedingly small flies, most 

 of which are " Egg parasites." Their bodies are rather slender and the 

 wings almost without veins, but in some species are fringed with fine 

 hairs around the edges. They breed, as a rule, in the eggs of larger 

 insects, of which they destroy great numbers. The family of the 

 CHALCIDID^E is also composed mainly of very small species, some of 

 which also breed in eggs, but usually in the bodies of other insects, 

 especially in those of Aphides. They are often of beautiful metallic 

 colors. The antennae are elbowed and have from six to fourteen 

 joints. A considerable number have the thighs of the hinder legs 

 very much thickened for jumping. The wings have very few veins and 

 no enclosed cells. In the male the abdomen is seven-jointed, while in 

 the female it has only six joints. Except in a very few species the ovi- 

 positor is entirely withdrawn into the body except when in use. They are 

 not infrequently parasitic upon other parasites, and, therefore, to be reck' 

 oned among injurious species. In this group, also, we find the de- 

 structive " Joint-worm flies" (Isosoma hordii Har. tritici and I. grander 

 Biley), which puncture the stalks of small grain at the joints in de- 

 positing their eggs, the larvae afterward feeding upon the sap, and 

 where they are numerous, preventing the growth of the stalk and the 

 filling of the head. Mr. F. M. Webster of Indiana made the discovery 

 that many of the females of I. grande were wingless. As most of these 

 insects hibernate in the straw, burning the latter after threshing and 



