170 



AN INTRODUCTION TO ENTOMOLOGY 



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

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

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



silk-like secretion (Fig. i! 



the locusts, Acridiidas, lay their eggs in 

 oval masses and cover them with a 

 tough substance; the scale-insects 

 of the genus Puhinaria excrete a 

 large cottony egg-sac (Fig. 189); 



^^ 





Fig. 187 — Egg-mass of the 

 squash-bug. 



Fig. 188. — Egg-ssLCot Hydrophilus 

 (After Miall). 



Fig. 189. — Pulvinan'atnnumerabUis, females on 

 grape with egg sacb 



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

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

 egg-cases, termed 

 ootheca, 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 

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

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

 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 

 m a i> *^^^*^^ 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 



i:)D. 



o f 



