30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



(1, 2, j) from the hypopharynx being inserted on a sclerotic bar, 

 or rhaphe (Rph), in the dorsal wall of the press, and a single pair 

 from the labium (4) attached laterally. The lumen of the press is 

 continued into a narrow exit tube (D) that opens on the end of the 

 spinneret (Spn). The hypopharyngeal wall of the press is deeply 

 inflected (E) into the lumen (Lum), but evidently can be lifted by 

 the muscles, and then by an elastic springback drive the liquid silk 

 from the spinneret. The silk press is probably also a silk ejection 

 pump. 



As already noted, the maxillae are closely associated with the labium, 

 forming a prominent lobe on the underside of the head bearing the 

 spinneret (fig. 5 B,C), but the hypopharynx (Hphy) also is involved 

 in this structure, since it is united with the inner wall of the labium 

 (Lb). While these parts are movable by their own muscles, the 

 characteristic figure-eight movements of the spinning caterpillar are 

 made by the head and the freely swinging fore part of the body, 

 activated by the elaborate head and body musculature (fig. 11 A,B). 



When the caterpillar in its evolution had once become fully adapted 

 structurally for the performance of its functions in relation to its 

 future pupal and adult state, its successors were then free to vary 

 in superficial ways, and to adopt habits suitable to their own interests. 

 So, as the adults in their evolution were diversified into many species, 

 their caterpillars likewise underwent evolutionary changes as they 

 adopted different ways of living and feeding, until they became as 

 distinctive of their species as the adults. Though most caterpillars 

 have remained vegetarians, feeding in the open on the leaves of herbs 

 or trees, some have penetrated the fruit, others have taken to mining 

 the leaves, boring into stems or wood, or burrowing into the ground, 

 while a few have become aquatic and have developed gills in the form 

 of slender tracheated filaments growing from the back. All these 

 are plant feeders. 



There are species of caterpillars, however, that have renounced 

 vegetarianism for other kinds of food. A good review of these 

 aberrant feeders has been given by Brues (1936), and Clark (1926) 

 has described the carnivorous caterpillars. The wax moth invades 

 beehives and its larvae burrow destructively through the honeycomb, 

 feeding on the wax and the bees' store of pollen. Larvae of the clothes 

 moth eat fur, wool, and feathers. A number of species have become 

 carnivorous, feeding as predators on live aphids, larval coccids, other 

 young homopterons, pupae of moths, spider eggs, and eggs of the 

 bagworm. A lycaenid caterpillar has imitated the aphids by excreting 

 from glands on the end of its abdomen a liquid agreeable to ants. 



