66 



ENTOMOLOGY 



diffuses a characteristic but indescribable odor that is probably repellent. 

 The larva of Cerura everts a curious spraying apparatus from the under 

 side of the neck. 



Alluring Glands. Odors are largely used among insects to attract 

 the opposite sex. The androconia of male butterflies have already been 

 spoken of. Males of Catocala concumbens disseminate an alluring odor 

 from scent tufts on the middle legs. Female saturniid moths (as cecro- 

 pia and promethea) entice the males by means of a characteristic odor 

 emanating from the extremity of the abdomen. In lycaenid caterpillars, 

 an eversible sac on the dorsum of the seventh abdominal segment secretes 

 a sweet fluid, for the sake of which these larvae are sought out by ants. 



Wax Glands. Wax is secreted by insects of several orders, but es- 

 pecially Hymenoptera and Hemiptera. In the worker honey bee the 



wax exudes from unicellular hypo- 

 dermal glands and appears on the 

 under side of the abdomen as four 

 pairs of wax scales (Fig. 102). 

 Plant lice of the genus Schizoneura 

 owe their woolly appearance to 

 dense white filaments of wax, 

 which arise from glandular hypo- 

 dermal cells. In scale insects, 

 waxen threads, emerging from 

 cuticular pores, become matted 

 together to form a continuous 

 shield over and often under the 

 insect itself, the cast skins often 

 being incorporated into this waxen 



scale. The wax glands in Coccidae are simply enlarged hypodermis 

 cells. 



Silk Glands. Larvae of very diverse orders spin silk, for the purpose 

 of making cocoons, webs, cases, and supports of one kind or another. 

 Silk glands, though most characteristic of Lepidoptera and Trichoptera, 

 occur also in the cocoon-spinning larvae of not a few Hymenoptera (saw 

 flies, ichneumons, wasps, bees, etc.), in Diptera (Cecidomyiidae), Neurop- 

 tera (Chrysopidae, Myrmeleonidae), and in various larvae whose pupae are 

 suspended from a silken support, as in the coleopterous families Coccinel- 

 lidae and Chrysomelidae (in part) and the dipterous family Syrphidas, as 

 well as most diurnal Lepidoptera. 



The silk glands of caterpillars are homologous with the true salivary 



FIG. 103. Head of caterpillar of Samia 

 cecropia. a, antenna; c, clypeus; /, labrum; 

 Ip, labial palpus; m, mandible; mp, maxillary 

 palpi; o, ocelli; s, spinneret. 



