244 BRITISH LEPIDOPTERA. 



The gregarious habit usually lasts until the third moult, occasionally, it 

 is stated, to the fourth. In very suitable weather the first ecdysis takes 

 place in about 6 days from hatching, the second some 6 days later, 

 another 6 days is sufficient for them to have completed the third 

 moult, whilst the fourth takes place some 7 or 8 days after the 

 third ; the larvae then feed for about a fortnight after the fourth moult 

 betore they attain full growth. Sometimes, however, almost double this 

 time is required in the early stadia. When almost fullgrown the larvae 

 are very lethargic, show no disinclination to be handled, rest side by side, 

 and have a most contented appearance. When, however, quite ready 

 for pupation, they become restless and wander about until they find a 

 suitable position in which to pupate (Tutt). The young larva 

 nibbles a hole at one end of the egg, and half-an-hour is generally 

 sufficient for the majority to clear. They wander over the shells, 

 gently feeling each other as they come in contact, and, starting a 

 trail, commence their first journey in life ; one leaves the batch, 

 makes its way up a twig, followed by the others in single file, 

 following the leader, and if one " loses trail," it tries back until it has 

 again fallen into the line of march. They then assemble near the 

 tip of a twig, adhering when at rest by the claspers, the anterior 

 portion of the body being erect, and closely resemble in colour, 

 shape and size, the little black stumps so common on the twigs of 

 birch. Another part of the batch may go off in another direction, 

 having failed to strike the original trail. When the produce of a 

 batch divides into two companies it frequently happens that, when 

 removing in search of fresh food, each part, descending its respective 

 twig, falls into a common trail on the main twig, becoming united, 

 probably to be again divided at a subsequent migration. When 

 some ten days have elapsed the body thickens, the larva ceases 

 to eat, the head slips out of its old cover (which is empty and 

 transparent) into the prothorax, the skin breaks down the back, and 

 is slipped off segment after segment until it is gathered into a 

 little heap behind. The first moult singles out the weak or diseased 

 individuals, which die under, or without accomplishing, the opera- 

 tion. The larvae, now of a dull green colour, bear, as they sit in 

 groups, a remarkable resemblance to bunches of the birch-catkins, 

 and it requires a practised eye and close examination to distinguish 

 one from the other. At times, when resting in small groups, or 

 even singly, in a reflexed posture, the rigid prolegs extend and 

 give an outline more or less resembling the mid-rib and serrated 

 edges of a birch-leaf, and the larvae evidently trust to these attitudes 

 for concealment. They still continue to feed in groups, marching 

 in company from branch to branch as the food becomes exhausted ; 

 the groups appear to feed systematically, the larvae going out two 

 or three at a time to the neighbouring leaves, and returning to fall 

 in, others advancing to take their place ; after about ten days 

 more the second moult takes place, after which the larvae, becoming 

 too large to derive security from their resemblance to the catkins, 

 disperse, their attitude and colour daily assuming more resemblance 

 to a leaf. After another moult they grow rapidly, feed incessantly, 

 and become very handsome ; and, in this stage, the female larva may be 

 distinguished from that of the male, being far more robust and sluggish. 

 When fullfed the larvae assume a rosy tint, and then go down into the 



