Fig. 191—Cocytia durvillii. New Guinea. (After Boisduval.)
Fam. 10. Cocytiidae.—A single genus constitutes this family, and there are only three or four species known; they come from the region of New Guinea, whence the first was brought by D'Urville nearly a hundred years ago. They are still amongst the rarest of Insects. Nothing is known as to their life-histories. In appearance they somewhat remind us of the Bee-hawk moths and Zygaenidae. Butler says[[261]] the family is characterised by the palpi, which differ much in the two sexes, and by the antennae resembling those of Castniidae or Hesperiidae. The form, transparency, and coloration of the wings reminds one vividly of the Sphingid genus Hemaris; the nervuration is somewhat like that of Hemaris, but has certain features of Zygaenidae. Butler places the family between Agaristidae and Zygaenidae.
Fig. 192—Cerura vinula (Puss-moth) caterpillar. A, Moulting; B, the same individual a few hours after the moult.
Fam. 11. Notodontidae (Prominents, Puss-moths, etc.).—This is one of the most extensive of the families of Bombyces; it consists in larger part of obscure-coloured moths, somewhat like the ordinary Noctuidae of temperate regions; to which family the Notodonts are indeed considered to be very closely allied. The family contains, however, some very remarkable forms. Tarsolepis has an elongate body, terminated (in the female of T. fulgurifera) by a very conspicuous tuft of enormously long, battledore scales; while in the male of T. sommeri the hind legs are provided with an appendage of beautiful, roseate hairs. A few of the larger kinds bear a considerable resemblance in form and proportions to the Sphingidae. Some of the larvae are most interesting objects; the Puss-moth caterpillar, the Lobster, and the Dragon larvae are of such strange forms that they have already interested several generations of observers. The Puss-moth is common in the southern half of England; its caterpillar (Fig. 192) has, instead of the claspers, a pair of tubes in which are concealed two long, flexible whips, capable of being thrust out, and withdrawn, with rapidity. The structure and the mode of action of these flagella have been well elucidated by Professor Poulton.[[262]] The flagella are to be considered as actual prolongations of the receptacle in which each is placed, though they are of very different texture therefrom; they are everted by blood-pressure and drawn in by muscular action; this latter function is very perfectly accomplished, the amount of relaxation and contraction of the muscle being very great. It has been maintained that the whips have arisen as arms of protection against the attacks of Ichneumon flies; observation shows, however, that the proportion of these "protected" Insects destroyed by enemies of this sort is quite as large as it is in the case of forms that are not so protected. The Puss-moth larva is also believed to be protected by terrifying attitudes,[[263]] as well as by ejection (like so many other larvae and insects generally) of fluid. There is no reason for believing that these larvae are less eaten than others, and consequently a further hypothesis has been proposed, to the effect that if they had not acquired these means of defence they would have been exterminated altogether. This supposition is considered to account for their acquiring the defence by means of natural selection; realising the dictum of D. O'Phace, Esq.—
Some flossifers think that a fakkilty's granted,
The minnit it's proved to be thoroughly wanted.
When the Puss-moth caterpillar is full grown it spins a peculiar cocoon of a solid and impervious nature, which it manages to make look very like the spots, crevices, or other places amongst which it is located; in this prison the creature remains for nine or ten months—by far the larger part of its existence. When it has changed to a moth it has to escape from the cell in which it so effectually confined itself. This is effected by the cocoon being thinner in front of the head of the moth, and by the emission from the alimentary canal of a fluid that softens the cocoon at the spot alluded to. Mr. Latter has ascertained[[264]] that this fluid is strongly alkaline, and contains potassium hydroxide. The front of the head of the moth is provided with a shield, consisting of a portion of the pupa shell, which enables the moth to push through in safety, and at the same time protects the head from the emitted fluid. Figure 192 shows the great change that occurs in the period of a few hours in the size of the head of the larva, as well as in that of the spiracles: in A the old spiracles are seen surrounded by the much larger new orifices, which are at the moment of moulting quite visible through the skin that is about to be cast off.
The caterpillar of the Lobster-moth, Stauropus fagi, is more remarkable than that of the Puss-moth, but is unfortunately very rare. It has remarkably long thoracic legs, the abdomen is swollen at the tip, and instead of the terminal claspers has two long slender processes. The effect of these peculiarities is greatly enhanced by the extraordinary attitude assumed by the caterpillar, which holds the first five segments erect, with the second and third pairs of thoracic legs outstretched; the swollen terminal segment is also held erect. Hermann Müller states[[265]] that when seen from the front this caterpillar looks like a spider, and also that when alarmed it moves the long legs after the fashion of an Arachnid. He believes that it is thus effectually protected from the attacks of Ichneumons. Birchall says[[266]] that the young larva, when at rest, closely resembles, in colour and outline, one of the twigs of beech with unopened buds, on which it frequently stations itself; and that, when feeding, its likeness to a great earwig or to a Staphylinus is very striking. Others say that this caterpillar resembles a dead and crumpled beech leaf.