Butterfly Migrations in British Guiana. 333 



It will be noticed that the number of these insects passing 

 gradually decreased except in the last five minutes, but 

 even then it was considerably less than at the beginning 

 of the observation. 



At 2.20 p.m. observations were started at another point 

 about 650 yards east of the first position and about 80 yards 

 further south. The distance over which the insects were 

 counted was about the same as in the previous instance. 

 Here 143 butterflies crossed the area in five minutes, 

 making an average of 28" 6 per minute, a number which 

 was only exceeded during the first minute of observation. 



To get some idea of the speed at which the butterflies 

 were travelUng, a distance of about 22 yards was paced 

 off between two fences, and the insects crossing this space 

 were timed from the moment they mounted one fence till 

 they arrived at the next. Eight insects, taken at random, 

 were thus timed; they all crossed the distance in about 

 five seconds. This gives a speed of about 9"0 m.p.h. 



By 2.30 p.m. the decrease in the number of butterflies 

 was very noticeable, and I returned to the laboratory. By 

 2.45 p.m. the migration had ceased. 



The next day I wrote a letter to both local newspapers 

 asking any one who observed this migration to communicate 

 with me . Concerning this particular migration I got bub one 

 observation, though there were a few relating to other 

 migrations. 



The late Mr. John Cunningham, Editor of the " Daily 

 Argosy," informed me that while motoring along the East 

 Coast, Demerara, on that day he observed large numbers 

 of yellow butterflies in the vicinity of Paradise, which is 

 about 16 miles from Georgetown, going in an easterly 

 direction. On his arrival in Georgetown about 1.30 p.m. 

 he noticed them too. From this we may conclude that the 

 swarm was at least 16 miles in length. 



The facts concerning this migration may be summarised 

 as follows : — 



Duration of migration . . about 2| hours. 



Direction of migration . . East. 



Prevaihng wind . . . N.B. 



Speed of wind . . . 12*50 m.p.h. 



Speed of migration . . 9-0 m.p.h. 



Average number of insects 1 



crossing an area of about V 14-9 to 28-6 per min. 

 120 yards wide J 



