Butterfly Migrations in British Guiana. 163 



1913, p. 137, writes that he has " once witnessed a flight 

 of white butterflies {Appias Duirgariia) on the lower left 

 bank of the Berbice Kiver which lasted for over three days, 

 and could only be compared during the whole of that time 

 to a heavy snowstorm. And the extraordinary thing was 

 that they were all flying directly out to sea. Mr. Leechman 

 has informed me that this occurred in April 1909. 



It is difficult even from the above records to get any 

 indication of what is happening. On the real problem, 

 why the migration takes place, there is still no light, and 

 many more correlated observations must be made before 

 there can be any hope of solving it.* There are, however, 

 a few points to which attention might be directed. In the 

 first place, there are here two general directions of migra- 

 tion for Callidryas eubule, roughly from the north-west to 

 the south-east, and vice versa. There is as yet no record 

 of a migration in a north-east or south-westerly direction. 

 The prevailing wind is the north-east trade wind, so that 

 the migrations were across the wind. It is impossible to 

 say if this is the real determining factor in the direction of 

 the migration or not. 



Secondly, all the migrations of Callidryas in which the 

 date is recorded took place between May and October. 



Thirdly, it seems possible to distinguish between several 

 different types of migration. At least one can make a 

 rough but convenient grouping into three classes. (1) The 

 thick cloud, " like a snowstorm," a case which immediately 

 attracts the attention of the ordinary individual and is 

 most frequently recorded. (2) The diffuse migration, 

 which may vary from distinctly noticeable to so attenuated 

 that only a close observer would realise that anything 

 unusual was happening. There is, of course, no strict 

 line of demarcation between this and the last, and the 

 edge of a " cloud " migration would probably be diffuse. 

 A diffuse migration, however, can exist miaccompanied 

 by a cloud. (3) A particularly interesting form is the 

 " ribbon " migration, or " procession," in which a narrow^ 

 band of butterflies a few feet or a few yards wide flies 

 across the country in the direction of its length. The edge 

 of such a migration is well defined. In this connection 

 it might be mentioned that, even when not on migration, 



* British Guiana would seem to be a promising field for such 

 investigations, but they must be extended over a series of years, 

 with a number of competent observers stationed over the country. 



