170 



AN INTRODUCTION TO ENTOMOLOGY 



The laying of eggs in compact masses, however, is not correlated, 

 in most cases, with gregarious habits of the larvae. The water- 

 scavenger beetles, Hydrophilidse, make egg-sacks out of a hardened 

 silk-like secretion (Fig. i88) ; the locusts, Acridiidae, lay their eggs in 



oval masses and cover them with a 



,..► '^,.. -. .,^ tough substance; the scale-insects 



r ,! , , - of the genus Pulvinaria excrete a 



i"' •. ' V- _ \ large cottony egg-sac (Fig. 189); 



Fig. 187 — Egg- mass of the 

 squash-bug. 



Fig. 188. — Egg-sacoi Hydrophilus 

 (After Miall). 



Fig. 189. — Pulvinaria innumerabilis, females on 

 grape with egg sacs 



the eggs of the praying mantis are laid in masses and overlaid with 

 a hard covering of silk (Fig. 190) ; and cockroaches produce pod-like 

 egg-cases, termed 

 Gotheca, each 

 containing many 

 eggs (Fig. 191). 



Among the 

 more remarkable 

 of the methods of 

 caring for eggs is 



that of the lace-winged flies, Chrysopa. These insects place 

 each of their eggs on the summit of a stiff stalk of hard silk 

 (Fig. 192). 



Duration of the egg-state. — In the life-cycle of most insects, 

 a few days, and only a few, intervene between the laying of 

 p. an egg and the emergence of the nymph, naiad, or larva from 



— E g g- it. In some the duration of the egg-state is even shorter, the 

 ™ f- ^ I hatching of the egg taking place very soon after it is laid, or 

 pray- even, as sometimes in flesh-flies, before it is laid. On the 

 ^ ^ 2 other hand, in certain species, the greater part of the life of an 

 tis. individual is passed within the egg-shell. The common 

 apple-tree tent-caterpillars, Clisiocampa americana, lays 

 its eggs in early summer; but these eggs do not hatch till the fol- 

 lowing spring; while the remainder of the life-cycle occupies only a 



