1920] Fracker: Lepidoptera 169 



Of all the major orders, in only one, the Lepidoptera, have 

 the larvae attempted to meet the conditions of life as it exists 

 and, with minimum protection, succeeded solely through their 

 immense vitality. 



If the uniformity within each dominant order is remarkable, 

 the variety is no less so. The differences between the nearly 

 fifteen thousand species of Coleoptera in the United States are 

 primarily variations in essential chitiriized structures. Number 

 and position of legs true and false, number of claws, shape and 

 arrangement of mouthparts, head skeleton, cerci, and chitinized 

 plates are all evident. In the Diptera structural differences are 

 equally numerous; the soft parts such as body shapp, and the 

 respiratory system are also various. Dipterous larv^ depart 

 farther from typical arthropod structures than other orders. 



In the Hymenoptera structural divergences (once more 

 excepting Tenthredinoidea) almost disappear and variation in 

 social organization and methods of securing food take their 

 place. 



Again the Lepidoptera are unique. With a fundamental 

 structure so constant that logical classification long appeared 

 to be baffling, superficial differences in the larvae are extremely 

 numerous. One finds remarkable uniformity in all the principal 

 features of anatomy. The same number and position of thoracic 

 legs and prolegs, the latter nearly always with chitinized hooks, the 

 same form of head, the same kind of mouthparts, the same 

 number of spiracles and segments. Exceptions, except among 

 the few leafminers, are trifling. 



In superficial characters the reverse condition, variety, is 

 just as marked. Using one fundamental setal pattern, the most 

 diverse arrangements are presented. A sensitive area in one 

 family develops a single seta, in another, a tuft on a wart, in 

 another, a group of soft hairs on a fiat plate, and in still another, 

 a bunch of poisonous spines. If we examine the arrangement of 

 the hooks on the prolegs we will note variations equally 

 significant. 



FOOD SUPPLY 



Table I shows the remarkable uniformity in source of food 

 supply in the Lepidoptera. The members differ from other 

 orders in being confined almost entirely to chlorophyll-bearing 

 plants. The exceptions are entirely among the more primitive 



