ENEMIES OF PROTECTED INSECTS 219 



Let the number of o£fspring of any two parents destroyed 

 by each of these agencies be represented, in order as 

 above, by V, P (with above described Hmitations), p and 

 M : then if X be taken to represent the total number 

 of offspring, X — 1 represents the number destroyed by 

 all agencies together. So the equation can be written : 



X— l = V+P+i? + M. 



And the number destroyed by any one agent alone 



V = (X-l)-(P + 2? + M). 



It is obvious, therefore, that if, as is claimed, V is negligible 

 for protected species, P+2?+M must be correspondingly 

 greater, and there is some reason for thinking that this 

 is actually the case, although much statistical evidence 

 is required. 1 For instance, in the case of P, those who 

 have paid attention to, or observed in the field, predaceous 

 insects with their prey,^ have probably had the same 

 experience as myself, that the prey is very often among 

 precisely those species which are believed to escape 

 molestation by vertebrate enemies. Thus I found a com- 

 pany of spiny black and yellow larvae of Acraea perenna, 

 of which many had already been sucked dry by a bug,^ 

 which was found in the act of sucking one. This one 

 bug might very easily have destroyed seriatim the whole 

 of the brood of these aposematic larvae. In the case 

 of p we need especially comparative statistics showing 

 the relative proportions of aposematic and cryptic species 

 that are destroyed by parasites ; the following bears on 

 the subject. Acraea zetes, a typically aposematic scarlet 

 and black butterfly, abounded on Bagalla Island, and its 



1 See Trans. Ent. Soc. Land., 1902, part iii, pp. 328-38. 

 * See collected data by Poulton, Trans. Ent. Soc. Land., 19C6, part iii, 

 pp. 323-409. 



^ Damarius splendidulus. 



