148 



ENTOMOLOGY 



respiratory organs, such as the tracheal filaments of Simulium (Fig. 233),. 

 and the respiratory tubes of Culex (Fig. 232). 



Pupal Protection. Inactive and helpless, most pupae are concealed 

 in one way or another from the observation of enemies and are pro- 

 tected from moisture, sudden changes of temperature, mechanical shock 

 and other adverse influences. The larvae of many moths burrow into 

 the ground and make an earthen cell in which to 

 pupate; a large number of coleopterous larvae (Lach- 

 nosterna, Osmoderma, Passalus, Lucanus, etc.) make 

 a chamber in earth or wood, the walls of the cells 

 being strengthened with a cementing fluid or more or 

 less silk, forming a rude cocoon. Silken cocoons are 

 spun by some Neuroptera (Chrysopidae, Fig. 217), 

 by Trichoptera (whose cases are essentially cocoons) , 

 Lepidoptera* a few Coleoptera (as Curculionidae, 

 Donacia), some Diptera (as Itonididae), Siphonaptera, 

 and many Hymenoptera (for example, Tenthredi- 

 nidae, Ichneumonidae, wasps, bees and some ants). 



The cocoon-making instinct is most highly 

 oped in Lepidoptera and the most elaborate cocoons 

 are those of Saturniidae. The cocoon of Samia 

 cecropia is a tough, water-proof structure and is double (Fig. 218), 

 there being two air spaces around the pupa; thus the pupa is pro- 

 tected against moisture and sudden changes of temperature and from 

 most birds as well, though the downy woodpecker not infrequently punc- 

 tures the cocoon. S. cecropia binds its cocoon firmly to a twig; Trop&a 

 luna and Telea polyphemus spin among leaves, and their cocoons (with 

 some exceptions) fall to the ground; Callosamia promethea, whose cocoon 

 is covered with a curved leaf, fastens the leaf to the twig with a wrapping 

 of silk, so that the leaf with its burden hangs to the twig throughout the 

 winter. The leaves surrounding cocoons may render them inconspicu- 

 ous or may serve merely as a foundation for the cocoon. While silk and 

 often a waterproof gum or cement form' the basis of a cocoon, much 

 foreign material, such as bits of soil or wood, is often mixed in; the 

 cocoons of many common Arctiidae, as Diacrisia mrginica and Isia 

 Isabella, consist principally of hairs, stripped from the body of the 

 larva. 



Butterflies have discarded the cocoon, traces of which occur in 

 Hesperiidae, which draw together a few leaves with a scanty supply of 

 silk to make a flimsy substitute for a cocoon. Papilionid and pierid 



FIG. 217. Co- 

 coon of Chrysopa, 

 after emergence of 

 imago. Slightly en- 

 larged. 



