DANGERS OF THE DRY SEASON 209 



falls with especial severity on those still to be seen. Further- 

 more, the dry season forms are much less upon the wing 

 than the wet forms of the same species, and are apt to pass 

 long periods in a state of hybernation. Although drought 

 rather than cold is the probable cause of these periods of 

 torpor, the term hybernation is not inappropriate ; for 

 almost everywhere in southern Africa the dry season corre- 

 sponds with the winter, the wet with summer. Although less 

 upon the wing, the dry forms are commonly more alert and 

 active, and thus more difficult to catch than the wet. The 

 succession of broods is also nearly or quite at a standstill 

 in the dry season, so that the individual insects must endure 

 the repeated risks of a much longer life than those of 

 the other season, when the numbers are suddenly multi- 

 plied again and again by a series of brief generations. 

 Hence each individual of the dry phase is worth far 

 more to the species, and its loss is a much greater loss 

 than that of a short-lived individual of the other phase. 

 The risks during the periods of repose form a much larger 

 proportion of the total risks in the dry season than in the 

 wet. During these periods the insects are sought by 

 enemies different from those which pursue them upon the 

 wing and in the brief rests between short flights. It is 

 probable that the former enemies — insectivorous mam- 

 mals, reptiles, and birds which explore crevices for their 

 food — are less scrupulous in their tastes than those which 

 hunt alert and active butterflies. In the wet season, on 

 the other hand, butterflies are upon the wing in every 

 gleam of sunshine throughout their comparatively short 

 life ; and the enemies which they chiefly have to encounter 

 are those which pursue them on the wing or stalk them 

 in the brief intervals of rest. It has already been pointed 

 out that insectivorous forms generally are living in a time 

 of comparative plenty in the wet season. From these con- 

 siderations we can understand how it may be an advantage 

 to a somewhat distasteful species to be represented by 

 individuals with conspicuous warning (aposematic) colours 

 at a time when there is abundance of more palatable food, 

 and by well-concealed individuals at a time when food is 

 scarce and the struggle for life severe. 



POULTON 



