PLEBEIUS ARGUS. 211 



rate of feeding, for larvae that hatched on April 1st, 1903, were, on 

 June 1st, some in the second, others in the third, and yet others in 

 the fourth, instar, varying in length from 2*5mm. to 6*25min., yet 

 closely resembling each other in general appearance. Chapman 

 observes of some larvae he had under observation, on April 2nd, 1908 : 

 " The larvae, in glass tubes, on Ornithopus, are doing well, and take 

 readily to flowers of L'lex, being already in the third instar ; those on a 

 growing plant of Ornithopus are doing badly, and have dwindled from 

 more than forty to about hali-a-dozen, and these have only just entered 

 the second stadium ; whilst those put on Erica seem to have disappeared 

 altogether; of those larvae put on growing Ornithopus, there is one on a 

 small seedling-plant, growing up amongst the Ornithopus, as yet 

 unrecognisable, but not only not Ornithopus, but not leguminous; this 

 larva is to be seen eating this somewhat succulent seedling, and is in 

 better condition than any on the Ornithopus : being left on the little 

 plant, the larva continued to thrive thereon ; the plant also did well, 

 and finally proved to be Plantayo coronopus. The other larvae on the 

 growing plant of Ornithopus, were, from this date (April 2nd) reared in 

 a tube ; by May 3rd, these larvae were nearly all in the last instar, and 

 doing well on Ulex blooms. Several of them have some material like 

 white mould, on them, at or near the honey-gland, not quite perfectly 

 washed off with a camel-hair brush and water, but nearly so ; one or two 

 died in penultimate skin, apparently as a result of this mould attacking 

 the larva itself, but so far none have suffered seriously in the last skin. 

 Several are thinking of pupating, as evidenced by a little shrinking, a 

 blurring and fading of colours, so that the dorsal line is only faintly 

 brown, and the black hair- bases on it are more conspicuous, elsewhere 

 they are pale ; the green has taken on a sickly whitish shade ; the 

 prothorax is nearly colourless, and very translucent, taking its colour 

 more than before from the black head, when retracted. So far, no 

 definite attempt at a cocoon or a girth is observed. On March 31st, a 

 larva was observed moulting, the skin splitting nearly all the way 

 down one side, and forming a sort of balloon over the other side of the 

 larva. Usually, however, the skin opens more or less on both sides, 

 and then, as the larva emerges, shrinks back to about half its length. 

 A larva at its first moult, left its skin almost larger than before the 

 larva left it, and like a blown skin. The larvae do not eat their cast 

 skins. One larva (in a test-tube) bored a hole into the cork, apparently 

 with a desire to hide for pupation. The fullfed larvae, especially 

 when contracted and sulky, often show the ' fan ' glands (of the 8th 

 abdominal segment) whilst completely retracted, as small cones, or 

 perhaps better volcanic cones, the top being truncated." 



Symbiosis between labv^e of Plebeitjs argus and ants. — Plotz 

 records (Stett. Ent. Ztg., 1845, p. 115) finding larvae of P. argus on 

 Calluna vulgaris, and was much puzzled at seeing that every larva 

 had an ant standing on its back ; he also saw about 40 larvae near ant- 

 hills, the ants always on the larvae, standing or walking, and apparently 

 the larvae in no way incommoded or molested by them ; indeed, he 

 thought the ants seemed to try to protect the larvae from his interfer- 

 ence ; he adds that not one of these larvae was affected by ichneumons, 

 and all produced butterflies. Powell observes (Ent. Piec, xviii., p. 214) 

 that, in May, 1906, he found that larvae of this species, green in colour, 

 with a dull crimson dorsal line, possessed quite tall processes on the 



