236 
president’s address. 
out is too absurd for consideration. If any one thinks otherwise, 
let him try to find, in a piece of average fen, a living moth which 
he has accidentally dropped, and which he knows to he sitting 
quietly within a few inches. Where, however, the larva is 
collected, an element of danger comes in ; and if it feeds on a plant 
which, from its scarcity or its conspicuous nature and accessible 
position, offers facility for a thorough search, it is quite possible 
that extinction may result. Indeed, I believe that this has been 
the case in some instances, though I am by no means sure. 
A supposed case in point is the disappearance of the Black-veined 
White Butterfly ( Aporia crataigi) from localities in Kent where it 
was formerly abundant. At least I have seen more than one 
rather warm letter on this subject ; and it must be owned that 
many things seemed to indicate such a cause for its disappearance. 
The Butterfly was always curiously local ; and the larvae, though 
feeding on such abundant food plants as Whitethorn and Apple, 
yet were easily detected from their habit of feeding gregariously 
during their early life. But the insect occurred in a large number 
of localities scattered over a considerable area, though still with the 
same local habit, and it has disappeared from nearly, if not quite 
all of them, lingering longest near Dover and Bamsgate, where one 
specimen was taken last year. In 1871 I received a good series of 
the insect from Newport, Monmouthshire, with the assurance that 
I might at any time have as many as I liked, since it was in 
profusion there. I believe it was not more than three or four 
years later that my correspondent informed me that it had entirely 
disappeared from the locality, and that without any persecution by 
collectors whatever. Thus we must, I think, put aside almost 
entirely the idea of direct human agency in the extinction of 
insects. Indirectly, through the drainage of the Fens, man has 
no doubt done much to bring it about, but even this by no 
means accounts for the whole. I believe that where an insect is 
extremely local, if the same species is generally distributed in other 
parts of the world, we may conclude that it is a straggler beyond 
its proper geographical area (in which case the climatic conditions 
of its place of sojourn are probably unsuited to it). If, on the 
