226 



KNOWLEDGE 



[December 1, 1898. 



curiously tufted and tussocked caterpillar we alluded to on 

 a former occasion, employs its old cocoon as a receptacle, 

 or rather support, for its eggs. In every part of its 

 economy this insect is an odd creature. It is one of those 

 few Lepidoptera the females of which are practically 

 wingless. The male insect is a lover of bright sunshine, 

 and flies in search of its apterous and stay-at-home mate 

 during the hottest parts of summer days. As it is an 

 exceedingly common insect, and the caterpillar feeds upon 

 a variety of shrubs which are amongst those cultivated by 

 man, it makes itself quite at home in the gardens and 

 squares of our large towns, and may often be observed 

 gaily fluttering along the streets in the neighbourhood of 

 its home. It is a modest little broad-winged, russet- 

 coloured insect, with a crescent-shaped spot of white 

 towards the outer and lower corner of each fore-wing, and 

 with beautiful comb-like antennte. Its partner does not 

 rely upon beauty as a recommendation, for she is one of 

 the plainest-looking creatures imaginable, and it requires 

 a stretch of charity to refrain from calling her positively 

 ugly. She possesses the merest rudiments of wings, 

 though, as she never uses them, she might as well have 

 none at all. Her figure exhibits an excess of obesity 

 which, to the human eye at least, is suflSciently repulsive, 

 but apparently it has its attractions for her own kind, for 

 the males will come long distances for the honour of 

 becoming the possessors of her unwieldly frame. Her 

 body is clothed with a thick covering of x^ale greyish hairs. 

 She never leaves the cocoon which was the home of her 

 pupahood, but waits upon it tiU the arrival of her accepted 

 swain, after which she lays her eggs, scattering them over 

 the surface of the cocoon, the greater part of which they 

 are generally numerous enough to cover. This done, she 

 dies. 



The cocoon is loosely constructed ; the silk is fine and 

 glossy, but as many of the caterpillar's hairs are inter- 

 mingled with it, the texture appears coarse and irregular, 

 and the black brush-like hairs that belonged to the tufts 

 at the sides of the neck and at the tail are sometimes 

 conspicuous objects amongst the otherwise pale yellowish 

 mass (Fig. 5). The cocoon is not a complete one, like 



most of those described in our 

 last paper, but should rather 

 be described as simply a web 

 forming a roof arching over 

 the chrysalis, the surface of a 

 tree trunk or wall constituting 

 the base of support, and oc- 

 cupying the whole of the other 

 side. The chrysalis is of a deep 

 brown colour, and, strange 

 to say, is ornamented with 

 tufts of hairs on its difl'erent 

 segments, a feature which is, 

 however, characteristic of the 

 family. The scattering of 

 the eggs over the web may, 

 perhaps, in some way be con- 

 nected with the unusual circumstance that the eggs do not 

 all hatch at the same time, but the young caterpillars 

 continue to issue from them during a period of ten weeks, 

 so that eggs, caterpillars, pupse, and perfect insects may all 

 be met with at the same time during the summer. Another 

 species, called the scarce vapourer moth [Ori/i/in i/'ijwxtii/wa), 

 a much less common insect, has similar habits. 



It may be taken for granted that hairy caterpillars will, 

 as a rule, intermix their hairs with their silk, thereby 

 effecting a considerable saving of material ; but this is not 

 very different from saying that cocoons may generally be 



^isikis 





M.-^ 



FlO. 5. — Part of Cocoon uf 

 Tapourer Moth, sliowing one 

 of the black brush-like hairs. 

 Magnified six diameters. 



expected to contain hairs, for it is chiefly, though not 

 exclusively, hairy caterpillars that make cocoons, and the 

 longer and more numerous the hairs with which the 

 caterpillar is clothed, the larger will be the proportion they 

 will bear to the silk in the construction of the cocoon. 

 This is very manifest in the slight web formed by the 

 garden tiger moth {Airtin Cnja) ,. whose caterpillar, popularly 

 known as the "woolly bear," is the hairiest of a hairy 

 family. The web is thin, and the dark hairs are extremely 

 conspicuous. This is also true of the rest of the " tigers," 

 belonging to the same genus, and of the " ermines," 

 belonging to the genus Spilmdinn, and the colour of the 

 cocoon is, therefore, obviously determined largely by that 

 of the caterpillar's hairs. Now it is clear that if an attempt 

 were made to utilize the silk of such cocoons, the numerous 

 hairs scattered amongst and clinging to the threads would 

 become a serious inconvenience in the unwinding of the 

 silk, even should the threads of the latter be sufficiently 

 continuous to make such a procedure possible. It is 

 fortunate, therefore, that the silkworm of commerce is not 

 a hairy insect, for if it were, it would assuredly mingle its 

 hairs with its silk, and thus render its cocoon useless for 

 manufacturing purposes. The fact that it is hairy when 

 first hatched, though it loses its hairs almost entirely at 

 the first moult, seems to point either to an original adult 

 hairiness when in a wild condition, or at least to its descent 

 from hairy ancestors. As the present excellence of the 

 silk is, no doubt, due to long domestication and careful 

 selection, it is quite possible that a reversion to hairiness 

 of body in the adult condition would be accompanied by a 

 deterioration in the quality of the silk itself, quite apart 

 from what would result from the admixture of hairs. 



Amongst other curious lepidopterous cocoons may be 

 mentioned that of the lackey moth (Clisiocampa neimtria), 

 yellowish white, and supplied, when first formed, with 

 abundance of a pale yellow powder like flowers of sulphur ; 

 this is at first scattered through the silk, but gradually 

 collects into the lowest corner, and soon after falls out 

 altogether through the meshes. 

 The two beautiful moths called 

 "green silver lines" {Halias), 

 whose fore-wings are of a delicate 

 pale green with two or three 

 white or yellowish lines dravra 

 across them, make cocoons which 

 are like an inverted boat. Pass- 

 ing to exotic insects, we find some 

 very curious cocoons amongst 

 the silk-producing Bombyces ; 

 one of the most extraordinary 

 is that of the tusser silk 

 moth. This is a large moth 

 of a pale fawn colour, with 

 transparent circular windows in 

 the centre of its wings ; it is a 

 good deal reared in India for 

 the sake of the silk obtained 

 from its cocoon. The cocoon 

 is oval, hard, and compact, 

 without loose outlying threads, 

 seeing that it is not anchored 

 as usual, but is suspended at 

 the end of a stout stalk, the 

 further end of which forms a 

 circular loop tightly fastened 

 round some twig of the food- 

 plant, so that the cocoon hangs from the bough like a 

 kind of fruit (Fig. 0). 



Our next illustrations will be taken from the order 



Fio. 



0. — Cocoon of Tusser 

 Silk Moth. 



