246 THE VARIATION OF ANIMALS IN NATURE 



the distasteful properties of adult insects are the result of a 

 nauseous principle which was also serviceable to the larva. 

 Such direct transference of distasteful properties is quite 

 possible (cf. p. 247). Fisher suggests that the simultaneous 

 evolution of bright colours and distasteful properties in cater- 

 pillars could be evolved in species with the gregarious habit. 



In a number of moths all the offspring of one female feed in 

 a company together and, if a slight increase in distastefulness 

 were due to a mutation, it is possible that all or a considerable 

 number of the brood might share this property in common. 

 Then the tasting of one individual of the brood might save the 

 lives of his brothers, who would share his genotypic unpalata- 

 bility to an extent sufficient to discriminate in favour of the 

 gene. Even where the larvae are not strictly gregarious, but 

 the members of one brood live in moderate proximity to one 

 another, the territorial system of birds, which ensures that 

 any one pair of most of the smaller insectivorous species will do 

 their feeding during the breeding season over a single limited 

 area, might ensure the same result. 



It is true that certain distasteful insects (e.g. Acraea — Eltring- 

 ham, 191 2, p. 7) have gregarious larvae which appear, at any 

 rate from illustrations in the literature, to be rather con- 

 spicuous. But there seem to be many exceptions to the rule 

 (as admitted even by Fisher), and a number of conspicuous 

 larvae are not gregarious. The theory appears to be highly 

 speculative, and we have still to explain the origin of the gre- 

 garious habit. In connection with the latter point Fisher says 

 [I.e. p. 160) : ' The view that nauseous flavours have generally 

 been acquired by the effects of selection acting upon related 

 larvae living in propinquity, implies that gregariousness, or 

 equivalent habits, were formerly used by species which are 

 now distasteful, though it does not imply that species with 

 distasteful and even conspicuous larvae should necessarily 

 have retained the gregarious habit ; for the advantages of this 

 habit, among which we may surmise (1) the reduced exposure 

 of the female during ovipositions, and (2) in the case of dis- 

 tasteful and conspicuous larvae the advantage of increased 

 protection from predators, will not always counterbalance the 

 disadvantage sometimes entailed by a depletion of the food- 

 supply.' It appears that little light can be thrown on the 

 origin of the gregarious habit ; its very sporadic occurrence 



