488 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



A 



m 



also flat but have no other special characters, each being triangular 

 with a pair of teeth at the cutting angles. The outline drawings 

 in figure 2, B show on each the socket above and the knob below by 

 which the jaw is articulated to the head on a vertical axis, allowing 

 it to swing out and in but forbidding any grinding motion. The 

 jaws are excavating tools rather than organs of mastication. On 

 the edge of the lower lip (fig. 2, C) is a large hollow spine {Spn), 



the spinneret, through which the 

 ducts of the silk glands within the 

 body open to the exterior. We shall 

 see later the use which the cater- 

 pillar has for silk. 



The majority of the caterpillars 

 of the spring generation attain their 

 full growth by the latter part of 

 July, when they cease feeding, cut 

 out their cases from the mines, 

 hang them up on the twigs, change 

 to soft, orange-colored grubs, then 

 to pupae and transform to moths. 

 At this season only about two weeks 

 elapse between the cutting of the 

 cases and the appearance of the 

 moths. It is, however, seldom pos- 

 sible to set down exact dates for the 

 acts of any insect because its ac- 

 tivities always vary with the season 

 and with the latitude. In the north- 

 ern parts of a species' range the in- 

 dividuals have to hurry through 

 the summer stages in order not to 

 get caught unprepared for winter, 

 while in the south they may dally 

 along to a much, later date. Like- 

 wise, the same species may have only one yearly generation in the 

 extreme northern parts of its territory and go through several in the 

 southern parts. Hence, it is only a matter of local interest in the 

 study of any species whether it has one generation during the year or 

 six, though the determination of this as well as the approximate dates 

 often becomes a matter of much importance for the application of 

 control measures in the case of injurious species. 



The resplendent shield-bearer in southern New England and in 

 New York goes through two generations each season. The second 

 brood of moths, appearing during August, lays eggs which produce 

 the second or late summer brood of caterpillars, and these cause 



Fig. 2. — Mouth parts of the feeding 

 caterpillar of the Resplendent Shield- 

 Bearer. A, the upp<-r lip or labium ; 

 B, the jaws or mandibles ; C, the 

 combined maxillae (Mx) and labium 

 (Lb), situated below the mouth ; Spn, 

 the spinneret. 



