319] SOCTUID LARVAE— RIPLEY 77 



which situation they are protectively colored, those which can most rapidly 

 regain a favorable environment must survive natural selection in the course 

 of evolution. The many advantages gained by the power of rapid locomo- 

 tion are so obvious that a detailed discussion of them would be superfluous. 



Larvae of the ground and subterranean strata enjoy protection in a large 

 measure by virtue of their nocturnal and subterranean habits. The 

 proximity of their food to the ground, moreover, requires but little climbing 

 for them to reach it. In the older comparatively inactive larvae of such 

 forms the reduction of the first two pairs of uropods is generally not pro- 

 nounced. Caenurgia erechtea and certain phytometrids afford exceptions to 

 this rule. The occupation of the field stratum by the former species is very 

 unusual for larvae of the Catocalinae and is, therefore, to be regarded as a 

 biological specialization. The loss of the larvapods very possibly took 

 place in the ancestor of this species previous to its migration from the tree 

 to the ground stratum. However, this may be, the looping habit in noctuid 

 larvae appears to be generally correlated with a relatively active mode of 

 life and with one which often renders rapid locomotion especially advan- 

 tageous. It is never found among the cutworms or their biological allies, 

 except in the earlier stadia, being usually confined to the first two. These 

 instars are semiloopers in the family in all instances known to the author, 

 regardless of the gait of the older larvae. In the earlier stadia the larvae 

 are markedly more active than in the later ones. The small size and propor- 

 tionately long setae of newly hatched caterpillars render them decidedly 

 subject to conveyance by the wind, a matter of common observation. This 

 fact necessitates that they be generally more active than the older instars. 

 Moreover, the large number of individuals hatching simultaneously from a 

 single egg-mass demands dissemination either by the wind or by locomo- 

 tion, considerable activity being involved in either case. The threads 

 frequently spun only by the first instar serve as veritable parachutes in 

 some instances and as anchors by which they attach themselves to the food- 

 plant in others. The former employment of the thread, however, has not 

 been actually observed in the Noctuidae, so far as known, altho it has been 

 reported in other families and most probably occurs in this one. The 

 apparently universal presence of the looping gait in young noctuid larvae, 

 which is characteristic of the last instars of only the more active larvae of 

 the family, such as the catocalas, is not at all surprising when we consider 

 the especial need for rapid locomotion during the first one or two stadia. 



The appearance or increase in the relative size of the first one or two 

 pairs of larvapods during the postembryonic development of noctuid larvae 

 is obviously the expression of the unequal function of these structures in 

 different stadia. The extent of the reduction of these larvapods is propor- 

 tional to the extent of the development of the looping gait, which is cor- 

 related with the amount of advantage gained by greater or less rapidity in 



