HOW TO KNOW THE IMMATURE INSECTS 



61a. Dorsum of prothorax bearing on eversible, forked scent gland. 

 When the gland is retracted a transverse groove is revealed: 

 body not hairy or spiny, but sometimes with fleshy filaments. 

 Fig. 490 FamUy PAPILIONIDAE 



About 800 species have been de- 

 scribed. The caterpillars feed on 

 a number of plants, but chiefly 

 on Citrus and Umbelliferae. The 

 thorax of the larva is usually en- 

 larged, and sometimes possesses 

 two eyespots. A protrusible scent 

 gland on the dorsum which is 

 called osmeferium — is often pre- 

 sent and is ejected when the ca- 

 terpillar is disturbed. The adults 

 are the swallowtail butterflies. 



Fig. 490. Papilio cresphontes Cramer. 



61b. Not as 61a. 



,62 



62a. Head and body entirely without spines, high tubercles, or fleshy 

 filaments 63 



62b. Body with spines, higli tubercles, or fleshy filaments 65 



63a. Anal plate entire, rounded 34 



63b. Anal plate bifurcate at tip, bearing 2 distinct processes. 



Family SATYRIDAE 



64a. Head apparently larger than prothorax. . . Family NYMPHALIDAE 



64b. Head smaller than prothorax. Fig. 491 Family PIERIDAE 



About 1,000 species hove 

 been described. The caterpil- 

 lars feed on many kinds of 

 plants but are especially fond 

 of cabbages and other crucifer- 

 ous crops. The cabbage butter- 

 fly, Pieiis rapae (L.) is a cos- 

 mopolitan species and the rape 

 butterfly, Pier is napi (L.) is also 

 common to both Europe and 

 North America. 



FlQ. 491. Cabbageworm, Pi«rb r«pM 



(L.» 



172 



