1889.] 



THE YOUNG NATURALIST. 



H3 



there are conditions in which these rovers are unable to thrive, and 

 where these obtain, this is what is generally known as the utmost 

 range of the species. England naturally is the limit range of several 

 strong flying species, they reach us it is true at irregular intervals of 

 time, and in most uncertain numbers, but from climatic causes they 

 are unable to thrive here ; a few of them struggle to exist for a season 

 or two, but soon die out, and were it not for fresh arrivals by immi- 

 gration, our fauna list would soon know them no more. 

 Let us select a few cases. 



Colias hyale is of very uncertain appearance, abounding for a season, 

 and then perhaps lost to view for years ; as a day-flying species, it 

 could hardly fail to be detected if present with us. C. edusa varies 

 much in its numbers, but still it does occur, possibly every year. The 

 wonderful Edusa year (1877) I was spending six days in Tilgate Forest 

 the first week in June, when tattered specimens of Edusa occurred all 

 over the place ; we could have caught any number if so inclined. 

 These, of course, were the advance-guard of that wonderful abund- 

 ance that appeared the following August. The autumn previous 

 there had been no unusual number of Edusa, but here they were in 

 most unlikely places, and in abnormal numbers ; some of them were 

 extremely large — the largest I ever saw — but all of them were travel- 

 stained, i.e., ragged, and probably immigrants. 



Pirns daplidice and Argynnis lathonia are both of them rare visitants, 

 and apparently affecting no colony here. 



Vanessa antiopa is a good example of the second class. It has a 

 powerful flight, and a very wide range of distribution. It is common 

 through most of Europe, America, Canada, and in England it occurs 

 some years as a visitant in fairly large numbers ; in 1872 some 400 

 at least were reported. Yet, strange to say, the larva has never been 

 seen in this country. This is a remarkable fact, because the habit of 

 the larva is well known, and feeding gregariously on willows it could 

 not fail to be detected if present. It is not like an obscure night- 

 feeding species, and its non-detection must be accepted as a proof 

 that it cannot breed here, doubtless from some climatic reason. 



Anosia plexippus is another rare visitor. It has been taken in 

 Sussex, vide Entomologist, Vol. IX., page 267, and some ten specimens 

 were reported along the south-west coast of England in 1885, one of 

 which, captured in Cornwall by a friend, is now in my possession. 

 Here again we have every reason to believe that it has failed to 

 establish itself, although it has done so over a wonderful area, through 

 its great power of wing and roving habit. 



