340 , . THE ZOOLOGIST. 



Canton Zurich, on June 7th, an immense swarm moved from 

 S.W. to N.E., principally from 3 to 5 p.m. ; this flight went per- 

 sistently in one direction, only changing temporarily to avoid 

 houses and trees. At Steyer in Upper Austria, on June 11th, 

 surprising numbers flew ceaselessly from S.W. to N.E. ; between 

 1 and 2 p.m. 90 to 110 per minute were counted in a space of 

 about 100 paces, and the swarm was estimated to have been above 

 rather than below 1,000,000." 



These particulars, amongst others given by Mr. McLachlan, 

 will suffice to show the very extraordinary nature of the migration 

 of Vanessa cardui observed in that particular year. 



Commenting upon the facts, Mr. McLachlan says (l. c.) : — 

 " There can, I think, be little doubt that all the swarms consisted 

 of individuals that had hybernated ; there can also be little doubt 

 they were migrating, and that the column had become dispersed 

 before remnants of them reached our shores, and other parts of 

 the North of Europe. . . . Whence came they? Were they 

 all bred the previous autumn ? or is it possible the insect may 

 be able to rest quiescent in the perfect state over a series of 

 years until the accumulated numbers simultaneously wake up ? 

 The whole subject is surrounded with difficulties." 



When exhibiting the Ceylonese specimens, forwarded by 

 Mr. Mann, at a meeting of the Linnean Society on the 6th 

 of June last, I remarked that these curious flights of butterflies 

 could not be regarded as quite analogous to the migration of 

 birds, which travel in opposite directions in spring and autumn ; 

 for the insects travel only in one direction and do not return, vast 

 numbers perishing en route. The phenomenon resembles rather 

 what has been observed of Lemmings,* Locusts,f and Dragon- 

 flies,! and may be explained as a sudden exodus from the birth- 



* Crotch, Linn. Soc. Journ. xiii. pp. 27-34 (1878) ; additional note, p. 83. 

 Further remarks, pp. 157-160 pi. xiii. Collett, torn, cit., pp. 327-334. 

 Somerville, Proc. Zool. Soc, 1891, pp. 655-658. 



•j- See Layard, « Birds of South Africa,' pp. 291, 314 ; and Andersson, 

 ' Birds of Damaraland,' p. 2(54. 



I Several of the larger species of Libellula occasionally migrate, but the 

 phenomenon is of rare occurrence, and the circumstance which brings about 

 such an uncommonly numerous development of the perfect insect must be 

 very peculiar. See Weissenborn, on a remarkable migration of Libellula 

 depressa, Mag. Nat. Hist., n.s., vol. hi. p. 516; and Hudson, on "Dragonfly 

 Storms" (composed chiefly of Mzclma bonariensis) , 'The Naturalist in La 

 Plata,' pp. I."i0-134. See also Giitke, on the migrations of Libellula quadri- 

 punctata, Heligoland, p. 89, 



