1889.] 



THE YOUNG NATURALIST. 



31 



Sphinges this is particularly the case, as witness the Convolvuli years 

 1846 and 1887, and the Galii years 1870 and 1888 ; it is true also that 

 many species of insects travel great distances across the land and sea, 

 and that great migratory swarms of butterflies and moths have from 

 time to time been noticed. 



It is equally true that other species appear in certain seasons in 

 excessive abundance under circumstances which preclude the proba- 

 bility of any accession of numbers from abroad. Such small and weak 

 species as Tortrix viridana and Hyponementa padellus can not be supposed 

 to cross the ocean in order to appear in the tremendous numbers that 

 they do in certain seasons; I think that no one would suppose that 

 these were " blown-over." Again, in the case of Promissa, Sponsa, and 

 Quadra, I think that it is highly improbable that these in their abun- 

 dant seasons are increased from abroad. They are always present 

 with us ; one never hears of a summer in which not a single specimen 

 is taken. Furthermore, when they do appear plentifully, it is always 

 in those localities where a few may be taken in their scarce seasons, 

 chiefly in the New Forest. One never hears of Promissa appearing in 

 abundance in all parts of England or even in Ireland and Scotland ; 

 also in the case of these species {Promissa, Sponsa, and Quadra), I believe 

 it to be generally the case that the larva is abundant before the imago, 

 in fact, that they are natives bred and born. 



In the case of P. cardui is, I think, different. No one will deny 

 that it is a true indigenous British insect ; but from time to time it 

 would appear that the number in Britain is greatly increased from the 

 the Continent. The perfect insect appears in abundance without the 

 larva having previously been observed to be particularly plentiful. 

 A few years ago, I forget the year, a migratory swarm of Cardui and 

 Gamma was traced in its course from the southern part of Europe 

 northward, and part of the great swarm came to Britain. The same 

 is probably the case with Edusa. Both these insects are always with 

 us, but occasionally it would seem that their numbers are increased 

 by migration. 



When the case of such an insect as Galii is considered, I think that 

 most probably we shall find that it is — so far as Britain is concerned — 

 a purely imported species, and that in all probability our climate is 

 not suited for its permanent residence with us. We do not hear of 

 the larvae of Galii being found in England in 1887, but in the summer 

 of 1888 the perfect insects suddenly appear all round the coast. 

 Where do they come from ? Is it probable that they have been buried 

 as pupae since 1870 ? and if so, is it probable that such a cold season 



