i 3 6 



ENTOMOLOGY 



is rather complex. Briefly, while the larval skin still retains its hold on 

 the support, the posterior end of the pupa is withdrawn from the old 

 integument and by the vigorous whirling and twisting of the body the 

 hooks of the terminal cremaster of the pupa are entangled in the silken 

 support. At first the pupa is elongate (E) and soft, but in an hour or so 

 it has contracted, hardened, and assumed its characteristic form and 

 coloration (F). 



Pupal Respiration. Except under special conditions, pupae breathe 

 by means of ordinary abdominal spiracles. Aquatic pupae have special 

 respiratory organs, such as the tracheal filaments of Simulium (Fig. 231), 

 and the respiratory tubes of Culex (Fig. 230). 



Pupal Protection. Inactive and helpless, most pupae are concealed 

 in one way or another from the observation of enemies 

 and are protected from moisture, sudden changes of 

 temperature, mechanical shock and other adverse in- 

 fluences. The larvae of many moths burrow into the 

 ground and make an earthen cell in which to pupate; 

 a large number of coleopterous larvae (Lachnosterna, 

 Osmoderma, Passalus, Lucanus, etc.) make a chamber 

 in earth or wood, the walls of the cell being strength- 

 ened with a cementing fluid or more or less silk, form- 

 ing a rude cocoon. Silken cocoons are spun by some 

 Neuroptera (Chrysopidae, Fig. 215), by Trichoptera 

 (whose cases are essentially cocoons), Lepidoptera, 

 a few Coleoptera (as Curculionidae, Donacia), some 

 Diptera (as Cecidomyiidae), Siphonaptera, and many 

 Hymenoptera (for example, Tenthredinidas, Ichneu- 

 monidae, wasps, bees and some ants). 



The cocoon-making instinct is most highly developed 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. 

 216), 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; Tropcea 

 luna and Tdea 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 inconspicuous 



FIG. 215. Co- 

 coon of Chrysopa , 

 after emergence of 

 imago. Slightly en- 

 larged. 



