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XV. The Evolution of the Habits of the larva of Lycaena 

 arion, L. By T. A. Chapman, M.D. 



[Read October 4th, 1916.] 



In presenting my observations on L. arion last year to the 

 Entomological Society, I confined myself to the bionomics 

 actually observed ; nor had I thought out more than 

 some very vague ideas as to how the remarkable habits of 

 the larva had come about. A luminous comment by Mr. 

 Bacot, however, made a starting-point for endeavouring to 

 co-ordinate our knowledge towards its explanation. Like 

 many such valuable suggestions it seems so simple and so 

 probably true, that one feels sure that one surely had 

 thought of it all the time. Yet I don't suppose that I or 

 any one else had clearly done so till Mr. Bacot brought his 

 trained acumen to bear on the point. Mr. Bacot's supposi- 

 tion is that " the doing away with moults after the entrance 

 to the nest is a precaution against the temptation to the ants 

 of a soft, newly-moulted larva." The initial point in the 

 evolution of these habits would probably be that found in 

 the case of those " blues " whose larvae are collected by the 

 ants and placed on food-plants actually on the ants' nest, 

 as occurs with argyrognomon, coridon and bellargus and 

 probably other species. It may be a question whether the 

 nest is not actually extended towards a suitable plant, 

 but where this occurs plants and ants' nests are both 

 numerous, so that their coincidence in locality is necessarily 

 frequent. It might be said that the ants do take these 

 larvae to their nests, as they leave them, when at rest, on the 

 root stocks of their food-plants, and cover them with loose 

 material ; and I have seen ants remove a small larva that 

 they appeared to think in danger when I disturbed them. 

 A slightly deeper enclosure in the nest, and a cannibal 

 proclivity on the part of the larva, would initiate the arion 

 habit. 



The normal number of moults in Lycaenines is four, and 

 the normal instar for hibernation of those that hibernate 

 as larvae is the third instar. I have not found any accurate 

 record of these points in regard to the congeners of arion 



TRANS. ENT. SOC. LOND. 1916.— PARTS III, IV. (APRIL '17) 



