MR. B. SPRUCE OK INSECT-MIGRATIONS IN SOUTH AMERICA. 357 



could ascertain, are composed only of males"*. It is possible, 

 therefore, that in the flights witnessed by myself the individuals 

 were aU males — in which case the flights should probably be looked 

 upon, not as migrations, but dispersions, analogous to those of male 

 ants and bees when their occupation is done, and they are doomed 

 by the workers to banishment, which means death. In the case I 

 am about to describe, however, the swarms certainly comprised both 

 sexes, although I know not in what proportion ; and their move- 

 ments were more evidently dependent on the failure of their food. 

 In the year 1862 I spent some months at Chanduy, a small vil- 

 lage on the desert coast of the Pacific northward of Gruaya- 

 quil, where one or two smart showers are usually all the rain that 

 falls in a year : but that was an exceptional year, such as there 

 had not been for seventeen years before — with heavy rains all 

 through the month of March, which brought out a vigorous her- 

 baceous vegetation where almost unbroken sterility had previ- 

 ously prevailed. In April, swarms of butterflies and moths ap- 

 peared, 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 (FroelicMa, sp. n.) not 

 unlike our common Ribgrass in external aspect — until caterpillars 

 swarmed on every plant. Xew legions continued to pour in from 

 the east, and, finding the field already occupied, launched boldly 

 out over the Pacific Ocean, as Magalhaens had done before them, 

 there to find a fate not unlike that of the adventurous navigator f. 

 No better luck attended most of the ofi'spring of their predeces- 

 sors, especially those who fed on the Boerhaavia, which was much 

 less abundant than the I'Tcelichia. The shoal of caterpillars ad- 

 vanced continually westward, eating up whatever to them was 

 eatable, until, on nearing the sea-shore 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 Boerhaavia 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 movement 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 few rem- 



* ' Naturalist on the Amazons,' vol. i. p. 249 



t Here also the course attempted to be steered by the insects was across the, 

 strong southerly breeze that was blowing. 



LINN. PROC. — ZOOLOGT, VOL. IX. 28 



