ANIMAL MIGRATIONS 369 



In April swarms of butterflies and moths appeared, 

 coming from the east, sucking the sweets of the 

 newly-opened flowers, and depositing their eggs on 

 the leaves, especially of a Boerhaavia and of a 

 curious Amaranth (Frohlichia, sp. n.) not unlike our 

 common Ribgrass in external aspect until cater- 

 pillars swarmed on every plant. New legions 

 continued to pour in from the east, and finding the 

 field already occupied, launched boldly out over the 

 Pacific Ocean, as Magellan had done before them, 

 there to find a fate not unlike that of the adven- 

 turous navigator. 1 No better luck attended most of 

 the offspring of their predecessors, especially those 

 who fed on the Boerhaavia, which was much less 

 abundant than the Frohlichia. The shoal of cater- 

 pillars advanced continually westward, eating up 

 whatever to them was eatable until, on nearing the 

 seashore and the limit of vegetation, I used to see 

 them writhing over the burning sand in convulsive 

 haste to reach the food and shelter of some Boer- 

 haavia which had haply escaped the jaws of preceding 

 emigrants ; but, failing this, thousands of them were 

 scorched to death, or fell a prey to the smaller sea- 

 side birds, to whom they were doubtless a rare 

 dainty. 



The explanation of this continual westward move- 

 ment is not difficult. A few leagues inland, instead 

 of the sandy coast-desert with here and there a tree, 

 we find woods, not very dense or lofty, but where 

 there is sufficient moisture to keep alive a le\\ 

 remnants of the above-mentioned herbs all the year 

 round, and doubtless also of the insects that feed 



1 Here also the course attempted to !><. -.U-eivd l>y the iiiM.vt> \va> arr<>>~, the 

 strong southerly liree/e that \va> blowing. 



VOL. II 2 I: 



