302 



AN INTRODUCTION TO ENTOMOLOGY 



'95); and recently Mr. R. C. Smith ('21) has found that the larvae 

 of several of our native species have a similar habit. 



The cocoons are generally found on the lower sides of leaves or 

 on the supports of plants; they are spherical and composed of dense 

 layers of silk. In order to emerge the insect cuts a circular lid from 



^3+4 Mi+2 /?5 R^ ^1 



'''''^+^^v"^^^r^ 



Fig. 342. — Diagram of the wings of Chrysopa nigricornis, showing the coalesced 

 veins slightly separated. 



one side of the cocoon; this is done by the pupa by means of its 

 mandibles. After emerging from its cocoon, the pupa crawls about 

 for a short time before changing to the adult state. 



The adults are often attracted to lights at night. A remarkable 

 fact in the life-history of these insects is the way in which the female 

 cares for her eggs. When about to lay an egg she emits from the end 

 of her body a minute drop of a tenacious substance, which is probably 

 a product of the colleterial glands; this she applies to the object on 

 which she is standing and then draws it out into a slender thread by 

 lifting the abdomen ; then an egg is placed on the summit of this 

 thread. The thread dries at once and firmly holds the egg in mid-air. 

 These threads are usually about 12 mm. in length, and occur singly 

 or in groups; a group is represented attached to a leaf in Figure 339. 



About fifty species belonging to this family have been found in 

 the United States and Canada ; the greater number of these belong 

 to the genus Chrysopa. 



