MIGRATION AND DISPERSAL OF INSECTS : LEPIDOPTERA. 145 



Migration and Dispersal of Insects : Lepidoptera. 



By J. W. TUTT, F.E.S. 



Piepers further states that Avhen swarms of butterflies have been 

 observed at sea they must have been carried out, and that their flight 

 is, in such cases, entirely invokmtary, and beyond the control of the 

 individuals comprising the swarm. To emphasise his point that insects 

 cannot fly against the wind he notes that in 1899 a migration of 

 dragonflies in Holland was witnessed, and that all the observers stated 

 that the dragonflies came in against the east wind, but that on further 

 enquiry lie learned that although the wind was blowing from the east at the 

 levels of the tops of the houses (as judged by the direction of the smoke, &c.) , 

 at a height of three or four metres from the ground, where the dragonflies 

 were, there was no wind, owing to the obstacles, near the earth's surface, 

 and he expresses the opinion that this was the case, at the time that 

 Zeper observed, in the East Indies, a swarm of t'atoj>silia crocah' flying 

 against a wind of considerable force, a manner of flight which Piepers 

 asserts is impossible for butterflies. Our previous records suggest that 

 Piepers is entirely wrong, and that his assumptions, based on such 

 erroneous premises, are entirely unwarranted. Piepers concludes that, 

 in the East Indies, these migrations are not the result of a sudden 

 resolution taken by a number of individuals to leave the place of their 

 birth for another, but that there is at most, only a coincidence of 

 individual action. Each newly- emerged butterfly feels the need of 

 putting himself oi rtnjcKji' and fulfils this individual need, probably up 

 to that moment when he meets the individual of the other sex, who 

 attracts him, and with whom he leaves the swarm for the purpose of 

 copulation, and that, having paired, these particular butterflies no 

 longer follow the swarm, but commence to lead the life normal to 

 the ordinary mode of flight. He concludes, therefore, that it 

 is only because the number of butterflies which make simultaneously 

 the same choice is large, that their flight seems to be due to 

 common action. The facts on which he bases this conclusion 

 are not very weighty from the scientific standpoint. He observes that 

 no one has ever seen these migrating species leave one country and 

 arrive in another, and that the flights, as usually observed in the East 

 Indies, are not made up of a mass of collected insects moving in 

 common, but rather that, although they continue to move for a long 

 time in the same direction and in the same manner and many are 

 seen at the same time, they never form a band or crowd, and that only 

 in the districts between plantations of trees do they accumulate in any 

 numbers, using these as highways where they can more readily pursue 

 with advantage their onward flight. He further suggests that all those 

 observers who speak of " compact masses " or " nuees de papillons," 

 are misled by an intensity of expression to an overstatement of the 

 facts, and yet he is forced to the conclusion that a statement made by 

 bchonten, that he saw "nuees de ces papillons" in the island of 

 Salaiara in 1885, so many in fact that the butterflies {( 'atnjmlia cmcale) 

 in passage slightly intercepted the light of the sun as if a light 

 cloud was passing, cannot be passed over in this fashion, but he 

 attempts to explain the crowding as due to the butterflies being 

 huddled in a sharp angle, on the assumption that, having arrived from 

 the interior and reached the coast, they turned to follow the shore, 



