62 A NATURALIST IN THE TRANSVAAL. 



nonchalant manner. Even when a dried and neglected 

 museum-specimen, mites have avoided this butterfly, 

 while they have destroyed other insects in the same 

 box or cabinet-drawer. Its caterpillar feeds on a genus 

 of Asclepiadacese (Gomphocarpus) which is everywhere 

 abundant and also possesses distasteful qualities, so 

 that its whole existence seems to be environed by 

 natural clievaux de frise. How is it, then, that this 

 insect does not positively swarm 1 is the question I 

 frequently asked myself when watching the numbers 

 which everywhere pursued this highly protected life. 

 There must evidently be some great check at work, 

 or the propagation of the species must result in pro- 

 digious flights, which would surpass anything to be 

 seen in the whole Rhopalocerous order. I am inclined 

 to think that these highly protected butterflies, which 

 experience an immunity from attack on account of 

 distasteful qualities or resemblance to some inanimate 

 object or other protected insect, may have some inherent 

 weakness or danger which produces great mortality in 

 their early stages and that the wonderful protections we 

 observe thus only enable them to escape extinction. 

 This view would help to explain how it is that the extra- 

 ordinary guises by which natural selection has enabled so 

 many insects to escape the attacks of their enemies have 

 not led to an enormous increase in their numbers. It is 

 the weak that require protection, and like consumptive 

 patients who live by escaping the rigors of a northern 

 winter by visiting a warmer clime, but still possess the 

 inherent weakness of their system, so nature- grants 

 these insects immunity from one danger, which allows 

 them a possibility of surviving another. We know by 

 the great gaps between the continuity of some species 

 in the same genus how many must have reached 

 oblivion in the struggle for existence, and I look on 

 these " protected " insects as surviving by such means 

 some incipient mortality of which we are at present 

 ignorant, or their numbers must indefinitely increase. 

 I carefully watched the Danais in the endeavour to find 

 some danger to its life and the means by which its 



