JIIGRATION AND DISPERSAL OF INSECTS : LEPIDOPTERA. 255 



Migration and Dispersal of Insects : Lepidoptera. 



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



From the cold polai.' altitudes where Emjunia californiea is fighting 

 its way over the summit of Mount Shasta, we will transfer ourselves to 

 the hot Mississippi valley on the same continent and look at the 

 incredible abundance and subsequent dispersal of one of the well- 

 known Hackberry hwiiQvfiie'ii, ('lilori)ipi' {Apatura) celth. In a report 

 which comes from Arkansas, Webster states {Imcct Life, i., p. 29) that 

 on May 14th and 15th, 1888, for a distance of about thirty miles along 

 the St. Francis river, " the shores were literally lined with the 

 butterflies. On stumps they would be packed so thickly, that, with 

 wings erect, they completely covered the surface. The sides of the 

 small steamer on which I was travelling were covered, and I counted 

 seventeen on the back of a deck-hand as he was going about his work. 

 When a landing was made, and I got off to examine the brush-wood, they 

 would rise up in clouds about me and get into my eyes and mouth, so 

 that I had to beat about with a bush to protect myself. The engineer 

 of the boat said he had been running on the river for fifteen years, but 

 never saw so many before. The inhabitants along the river were as 

 surprised as myself." Holzgang records {loc cit., p. 29) that on May 

 19th he was passing along the west side of the Mississippi valley, near 

 Memphis, up the Arkansas, when he observed a swarm of millions of the 

 same species flying along the road in a southerly direction. The species 

 i ust referred to (('/(^(yr/y^/r celt is) is an Apaturid, but another species, called 

 popularly a " Celtis " butterfly, although belonging to an entirely diffe- 

 rent group, the Libytha^ids, is recorded {loc. tit., vii., p. 357) by Knight 

 {teste Riley) as migrating in vast numbers in Texas in 1895. ToAvards 

 the end of August, Hi/patus bachwani was observed at San Marcos, 

 Texas, flying eastward in vast numbers, and from enquiries that were 

 instituted it was ascertained that, at this time, swarms of the butterflies 

 were observed flying in a general eastward direction over a territory 

 almost one hundred miles square. Riley notes the species as belong- 

 ing to the Carolinian fauna, but taken occasionally as far north as 

 Ontario, and he supposed that the wet and hot weather of August, 

 which followed a period of drought extending over June and July, must 

 have favoured the simultaneous emergence of an unusually large 

 number of these butterflies from their chrysalids and brought about 

 the primary condition under which the migratory instinct is made 

 active in certain insects. 



Tait records (7^7«^oH/., xxvii., p. 133) that whilst at Santos (in 1893) 

 the local neAvspapers reported that an immense SAvarm of "borboletas" 

 had iuA-aded S. Vicente, a seaside village near Santos. The insects 

 had arrived in such immense numbers that they formed a cloud Avhich, 

 it Avas reported, even obscured the sun. They iuA'aded the A'illage, 

 swarming into the houses. The greater portion of the SAvarm Avas said 

 to have passed over the village, with a strong Avind Avhich Avas bloAving 

 at the time oft' the land, and in the direction of the sea. Large 

 numbers Avere repoi-ted to have fallen into the sea and to have been 

 subsequently washed ashore. Tait foimd the moths strcAved along the 

 shore and to be a species closely resembling the European Puss moth 

 {( 'enira rimda) but they were too much danuiged for actual identifica- 

 tion. The same observer also makes some remarks as to the influence 

 Septe.aiber 15th, 1901. 



