( 315 ) 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)
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