( iv ) 



He also showed specimens of the " Argentine Ant," Irido- 

 myrmex humilis, taken at Enfield and Eastbourne, and re- 

 marked that in the latter locality it had been established for 

 nearly twenty years as he was told, and had become a great 

 pest in many houses ; he also pointed out how it had spread 

 in America. 



Migration op Libythea labdaca at Freetown, Sierra 

 Leone, May 6, 1915. — Mr. A. W. Bacot exhibited specimens 

 of the butterfly Libythea labdaca and read the following 

 notes :— 



" The passage of these insects in large numbers attracted 

 general attention at 9.30 a.m., the flight continuing until 

 10.50 or 11 a.m. The steady stream of butterflies across the 

 hospital compound, when my attention was drawn to the 

 migration at 10.15 a.m., seemed to average about one per 

 square yard of area. The nature of the ground, bushes, 

 buildings, etc., tended, however, to give the stream a much 

 greater concentration at certain points, so that it was possible 

 to catch several at a single sweep of the net. By 10.45 their 

 numbers had gradually dwindled to a few scattered individuals 

 in view at the same moment. 



" The migration was in an E.N.E. direction following the 

 trend of the shores of the estuary, up river, against a steady 

 but not very strong N.E. breeze. In width the stream ap- 

 pears to have been at least one-third of a mile, as the insects 

 were observed throughout the town from the beach up to the 

 Governor's house. The flight across the hospital compound 

 was about 4 or 5 feet from the ground, and the speed would 

 not be less than 6 to 8 miles per hour. The insects rose at 

 walls and buildings, just sufficiently to clear the obstruction, 

 falling immediately on the further side to the old level, and 

 rising again in the same manner at the next obstacle. My 

 impression was that this close approximation to contour was 

 deliberate, in order to avoid the full force of the wind at 

 higher levels. In the late afternoon I observed occasional 

 stragglers taking the same direction with the sea breeze, 

 which had then set in, behind them, but all these individuals 

 flew high and wild without the same apparent regard for 

 contour. 



