62 



KNOWLEDGE. 



[April 1, 1898. 



of summer, and are covered over by the mother with a 

 layer of varnish. Towards autumn they hatch, but the 

 young larvie remain throughout the winter crowded together 

 under the waterproof skin so thoughtfully provided for 

 them. When the leaves appear in spring the little creatures, 

 which throughout their life seem to have a wonderful 

 faculty of looking after their own safety, come out from 

 their shelter, and begin to burrow into the young leaves, 

 devouring the soft matter underlying the cuticle, and thus 

 exchanging the protection of their dome of animal varnish 

 for shelter by a flat vegetable roof, which the leaf-skin now 

 constitutes over their heads. When they have grown suf- 

 ficiently, and their jaws have become strong enough to 

 attack the leaf from the outside, they come out of their 

 burrows and then begin to provide for their further safety 

 by spinning a web, under which they continue to carry on 

 the work of destruction. This will be their condition about 

 midsummer. This is the period of their life when they 

 are most annoying to the gardener, because when they 

 have finished the leaves enclosed in one web they migrate 

 to another spot and spin another, which they continue to 

 inhabit till their rapacity has again brought about a dearth 

 of food, when a further migration takes place. Thus, 

 during the course of their life, several webs may be formed 

 by the same batch, and the larger the colonies the more 

 fi-equent will be the moves, so that the trees soon become 

 covered with masses of sticky threads, which, quite apart 

 from the actual damage done to the trees, are annoying as 

 presenting an exceedingly untidy appearance. Sometimes 

 there will be from one hundred to two hundred caterpillars 

 in a single brood, and it is obvious that the daily provi,=,ions 

 required for such an army will be considerable. The 

 threads of the web, though apparently arranged quite indis- 

 criminately, run pretty much in the same direction, and 

 each caterpillar, forming its own line, seems to use that 

 as a kind of climbing ladder, in preference to those of its 

 neighbours. Hence results the parallelism of their position 

 when they crowd together in the centre of the web. They 

 run up and down their threads like sailors in the rigging 

 of a ship, and can go almost as rapidly backwards as 

 forwards. 



When they are full fed each caterpOlar spins a close- 

 fitting cocoon of its own inside the general web, and within 

 this it changes to a shining chestnut-coloured chrysalis. 

 As all the members of one colony belong to the same batch, 

 they all reach maturity about the same time, and form a 

 cluster of cocoons in the midst of the web. This change 

 is very rapidly made, the cocoon taking no more than a day 

 to construct, so that the result is rather striking — one day 

 we may see the wriggling caterpillars twisting about in the 

 web, full of life and energy ; the next, all is as still as death, 

 and in place of the active grubs there is only a closely packed 

 bundle of oval objects, reminding one of a cluster of "ants' 

 eggs " done up in cobwebs. Thus even in their chrysalis 

 condition they preserve their gregarious habits, while their 

 customary faculty of self-preservation is again strongly 

 asserted, for they are doubly protected, first by their own 

 cocoons, and secondly by the web outside. But when they 

 reach their perfect condition, an event which occurs in 

 .July, all these artificial aids to security are discarded, and 

 the little moths sit about on the tree trunks and on blades 

 of grass, as well as the leaves of their food-plant, in the 

 most prominent positions without any attempt at con- 

 cealment, their white satiny wings rendering them indeed 

 doubly conspicuous against the darker background of their 

 surroundings. They are, moreover, sluggish in the day- 

 time, and if disturbed do not fly far. If they once gain a 

 footing in a garden they are difficult to eradicate, and it is 

 not easy to discover remedies that may be entirely relied 



upon. Of course, the surest remedy is to cut off the shoots 

 on which the webs are found and burn them, but in bad 

 attacks this involves a great waste of material as well as 

 expenditure of time. 



Turning now to the more or less hairy caterpillars of the 

 Bombyces, we find one of the most noteworthy instances 

 of web-forming amongst British species in the small egger 

 moth {Krioyaster hrne.itris). This is in many respects a 

 remarkable insect. It feeds on hawthorn, and occurs 

 commonly on hedges in .June and July, tlie chrysalis being 

 formed in August. The moth appears, strangely enough, 

 not in the summer time, as most of the related species do, 

 but in February, sometimes in the next year to that of its 

 larvahood, but frequently not till another twelvemonth 

 has elapsed. In some cases a much longer time than this 

 intervenes before its final change, as much as five years of 

 pupahood having been recorded. This is a truly marvellous 

 instance of suspended vitality, since of course no food is 

 taken during all that period, and the moth is probably 

 fully formed within the chrysalis at the end of its first 

 winter. It is also remarkable that the insect should be 

 able to pass through the heat of the summer without 

 emerging, although that very heat is the necessary condi- 

 tion for the emergence of most Lepidoptera, and the factor 

 instrumental in producing that emergence. It is only fair 

 to note, however, that these long delays occur in confine- 

 ment, when the external circumstances are not altogether 

 natural, and of course it is impossible to say whether a 

 similar course is followed by the insect in the wild condi- 

 tion with its natural surroundings. 



The eggs are laid in spiral coils round the twigs of 

 hawthorn while they are still bare'of leaves (Fig. 2), and 



Fi&. 2. — Egg-Coil of Small Egger Motli, ou hawthorn twig. 



when laid they are wrapped round with dark grey wool, 

 derived from the end of the mother's abdomen, whereby 

 they are preserved from all the mischances that might other- 

 wise befall them during the three or four months that must 

 elapse before they are hatched. The ground colour of the 

 caterpillars is black, and they are ornamented with a few 

 bright yellowish spots and streaks ; they remain very much 

 of this appearance during all the first portion of their life. 

 Then comes a sudden change. At the last moult they 

 assume a reddish-orange coating, like velvet pile, on the 

 upper surface of each segment, and become very handsome 

 objects, so different from what they were before that they 

 might easily be taken for a different species. Soon after 

 hatching, the young caterpillars begin to surround them- 

 selves with a web, spinning the threads from twig to twig 

 around their birthplace, on which the remains of the 

 down-covered coil of egg-shells are still visible. As they 

 grow, and gradually devour the foliage immediately around, 

 the web is extended so as to enclose the twigs that are 

 stripped, the caterpillars dispersing in the neighbourhood 

 to feed at night, and returning to the nest by day. The 

 web (Fig. 3) is very different from that of the small ermine 

 moths, the threads being spun so close together and in 

 such dense masses that nothing can be seen of its internal 

 structure. When fully formed, it appears as a compact 

 angular mass, often as much as eight or ten inches in 

 diameter, and composed of white silk, usually more or less 



