60 DORSET LEPIDOPTERA IN 1892-3. 



specimen was noticed as early as May 1 2th, in Weymouth about 

 May 24th, in Purbeck on May 30th. The only at all satisfactory 

 theory to account for the sudden presence in numbers of this 

 species is that of immigration, though I believe that there is very 

 little, if any, direct evidence of it. It is, however, a well known 

 fact that butterflies do make very extensive migrations, as immense 

 swarms have not infrequently been observed at considerable 

 distances from land in the act of flight ; but I am not aware that 

 any theory has been put forward to account for this peculiar 

 instinct, nor is there known to be any regularity in the times of 

 its occurrence, so that we are still quite in the dark as to its cause. 

 The assembling of such vast multitudes into one mass is in the 

 first place most unusual in butterflies, which are not given to such 

 habits without some special external attraction, such, for instance, 

 as a field of lucerne, being present. The fact, however, of this 

 immigration seems incontrovertible, for the last appearance of the 

 species in anything like numbers was in 1877, since Avhich time 

 only a few stragglers in sheltered southern spots have been seen in 

 this country, added to which is the fact that those found here in 

 the early summer are not in sufiiciently good condition, when just 

 seen, to suggest the idea that they have lately emerged from the 

 chrysalis ; but, on the contrary, look like specimens which have 

 hibernated or at all events been on the wing for some time. That 

 they did not hibernate in this country is shown by the fact 

 that in 1891 the insect Avas at least very scarce, as I do not find a 

 single record of its occurrence in the Entomological magazines for 

 that year. The last year in which it was abundant was 1877, in 

 which it swarmed as in 1892. 



In the present year of 1893 Edusa has been abundant in some 

 parts along the S. Coast, but apparently locally, and not to any- 

 thing like the extent, either as to numbers or general distribution, 

 which it reached in the previous year. Personally I have seen 

 very few specimens in Dorset this year, and Mr. Cambridge's 

 experience is the same ; but it was abundant at Ringstead in 

 August, and from records in the Entom. magazines it woiUd appear 



