25 



amount of useful information, it at least established the fact that it 

 was easy to rear the species during the summer months, and the 

 opportunity was taken of its comparative abundance in some subse- 

 quent seasons to carry through furtheL- experiments, in which the 

 members of this society appear to have played a conspicuous part.^^ 

 It is perhaps hardly necessary to follow these through in detail, but 

 it may be briefly stated that they showed conclusively that a summer 

 brood was exceedingly easy to rear, but that as soon as the weather 

 began to cool in the autumn, difficulties arose with any brood of 

 larvae that was then feeding, the inference being that a certain 

 amount of warmth and sunshine was necessary for the well-being 

 of the larva. Cold weather appears to be equally fatal to the pupa, 

 comparatively few of those that assume that state late in the year 

 producing imagines, but it has been found that by keeping them 

 artificially in a temperature fully as warm as they would experience 

 in nature in summer, they may be induced to complete their meta- 

 morphoses even in winter, and arrive at maturity. ^'^ The egg-stage 

 does not appear to be capable of any great prolongation, lasting only 

 from one to three weeks, according to the temperature at the time 

 of year at which the ova happen to be laid; and although it has been 

 stated that the eggs are laid in spring by hybernated females,-^" I 

 can find no satisfactory record of the species ever having hibernated 

 in this country as an imago. The inference, therefore, appears to 

 be that in no stage can the species hibernate, in the sense of remain- 

 ing in a dormant condition through a protracted period, and that 

 our long, and sometimes severe, winters, would therefore more often 

 than not prove fatal to it ; in other words Britain is not its true 

 home. 



Colias ediisa, at any rate so far as concerns its westerly distribu- 

 tion, is essentially a Mediterranean species. It breeds regularly in 

 northern Africa and southern Europe, in the warm southern Alpine 

 valleys and other similar^ suitable inland places, gradually becom- 

 ing less common as one goes north, until in northern Germany it 

 is regarded as rare and uncertain in appearance ; yet it may be 

 found, sometimes not uncommonly, in Scandinavia, and has been 

 seen careering over the Alpine glacier passes at an altitude of at 

 least nine thousand feet ;-^ but in such places 't is evidently no 

 more at home than it is in Britain. It is, therefore, to the Medi- 

 terranean region that we must look for any reinforcement of the 

 species that is likely to produce those seasons of extreme abundance 

 that have been witnessed in Britain from time to time. That 

 migration on a large scale does take place among the butterflies 



w "Proc," 1895, p. 83; 1896, p. 25; 1901, p. 107. "Entom.," vol. 

 XXV., p. 201. 



!■' " Entom.," vol. xxvi., p. 60. 



-° "Entom.," vol. xviii., p. 21. 



-1 H. llowland Brown. "Butterflies and Moths At Home and Abroad," 

 p. 111. 



