THE WEB OF LIFE 285 



and straw-yellow. This Sarracenia moth (Xanthoptera 

 semicrocea) walks with impunity on the treacherous inner 

 surface of the pitcher and the female lays her eggs singly 

 near the mouth. The young larva spins for itself a carpet 

 of silk and draws the rim of the pitcher together with 

 a web which shuts out all other insects. It works its way 

 down the wall of the pitcher, devouring the cellular tissue, 

 and dropping large quantities of undigested food into the 

 cavity. It is a half-looper caterpillar, with beautiful cross 

 bands of white and purple or lake red, and prominent rows 

 of tubercles. * It keeps up, in travelling, a constant, rest- 

 less, waving motion of the head and thoracic joints, recall- 

 ing paralysis agitans. The chrysalis is formed in a slight 

 cocoon, usually just above or within the packed ex- 

 crementitious material. There are two broods in the 

 year'. 



Here we have two good examples of strange habitat 

 and strange mode of lif e. The flesh-fly is ' a mere intruder, 

 the larva sponging on and sharing the food obtained by the 

 plant '. The moth is an active enemy spoiling the Sarra- 

 cenia trap. 



Ants and Plants. The associations between ants and 

 plants show various degrees of intimacy. Ridley distin- 

 guishes three groups : (1) The ants may be sheltered within 

 the leaves or flowers, within hollow stems or thorns, and so 

 on, without deriving any food from the plant or conferring 

 any benefit on it. (2) In the case of some epiphytic ferns 

 and orchids, the ants that shelter about the base of the 

 plant bring up considerable quantities of soil. (3) Much 

 more intimate, however, are those cases where the ants live 

 in hollow stems, branches, or spines, and while feeding on 

 secretions exuded by glands of the plant, give this benefit in 



