Fam. 26. Limacodidae (or Eucleidae).—These are somewhat small moths, of stout formation, sometimes very short in the body, and with rather small wing-area. The family includes however at present many Insects of diverse appearance; there are numerous forms in which apple-green is a prominent colour; some bear a certain resemblance to the Swifts, others to Noctuids; some, Rosema and Staetherinia, are of extraordinary shapes; certain very small forms, Gavara, Ceratonema, resemble Tortricids or Tineids; a few even remind one of Insects of other Orders; so that the group is a mimetic one. Nagoda nigricans (Ceylon) has the male somewhat like a Psychid, while the female has a different system of coloration and wing-form. In Scopelodes the palpi are in both sexes remarkable; elongated, stiff, directed upwards and brush-like at the tip. Altogether there are about 100 genera and 400 species known; the distribution of the family is very wide in both hemispheres, but these Insects do not occur in insular faunas. In Britain we have two genera, Heterogenea and Apoda (better known as Limacodes[[289]]), each with a single species.
Fig. 200—Larva of Apoda testudo just hatched. A, Dorsal view of larva; B, C, D, a spine in different states of evagination. All magnified. (After Chapman.)
The early stages of these Insects are of great interest. The eggs, so far as known, are peculiar flat oval scales, of irregular outline and transparent; we have figured an example in Vol. V. Fig. 83. The eggs of the same moth are said to vary much in size, though the larvae that emerge from them differ little from one another in this respect. The latter are peculiar, inasmuch as they have no abdominal feet, and the thoracic legs are but small; hence the caterpillars move in an imperceptible gliding manner that has suggested for some of them the name of slug-worms. The metamorphoses of a few are known. They may be arranged in two groups; one in which the larva is spinose or armed with a series of projections and appendages persisting throughout life; while in the members of the second group the spines have only a temporary existence. At the moment the young larva of Apoda testudo emerges from the egg it has no conspicuous spines or processes, and is an extremely soft, colourless creature,[[290]] but it almost immediately displays a remarkable system of complex spines. These really exist in the larva when it is hatched, and are thrust out from pits, as explained by Dr. Chapman. In the succeeding stages, the spines become modified in form, and the colour of the body and the nature of the integument are much changed, so that in the adult larva (Fig. 199) the spines have subsided into the condition of mere prominences, different in colour from the rest of the surface. These larvae appear to be destitute of a head, but there really exists a large one which is retracted, except during feeding, into the body; the five pairs of abdominal feet of the larvae of allied families are replaced by sucker-like structures on the first eight abdominal segments. The spinneret of the mouth is not a pointed tubular organ, but is fish-tailed in shape, and hence disposes the silky matter, that aids the larva in moving on the leaves, in the form of a ribbon instead of that of a thread. It has been stated that these peculiar larvae "imitate" the coloured galls frequently found on the leaves of trees. The North American forms of this family have very varied and most extraordinary larvae.[[291]] In the pretty and conspicuous larva of Empretia stimulea, the tubercles or processes of the body are, in the later stages, armed with hairs, that contain a poisonous or irritating fluid, said to be secreted by glands at the bases of the processes. These hairs are readily detached and enter the skin of persons handling the caterpillars. The larva of the North American Hag-moth, Phobetron pithecium, is a curious object, bearing long, fleshy appendages covered with down. Hubbard makes the following statement as to the instincts of this larva:[[292]]—"The hag-moth larvae do not seek to hide away their cocoons, but attach them to leaves and twigs fully exposed to view, with, however, such artful management as to surroundings and harmonising colours that they are of all the group the most difficult to discover. A device to which this Insect frequently resorts exhibits the extreme of instinctive sagacity. If the caterpillar cannot find at hand a suitable place in which to weave its cocoon, it frequently makes for itself more satisfactory surroundings by killing the leaves, upon which, after they have become dry and brown in colour, it places its cocoon. Several of these caterpillars unite together, and selecting a long and vigorous immature shoot or leader of the orange tree, they kill it by cutting into its base until it wilts and bends over. The leaves of a young shoot in drying turn a light tan-color, which harmonises most perfectly with the hairy locks of the caterpillar covering the cocoon. The latter is, consequently, not easily detected, even when placed upon the exposed and upturned surface of the leaf."
The cocoons of Limacodidae are unusually elaborate, the larva forming a perfect lid in order to permit itself to escape when a moth. Chapman states that the larva lies unchanged in the cocoon all winter, moulting to a pupa in the spring, and that the pupa escapes from the cocoon previous to the emergence of the moth.[[293]] Both Chapman and Packard look on the family as really nearer to Microlepidoptera than to Bombyces; Meyrick (calling it Heterogeneidae) places it at the end of his series Psychina next Zygaenidae.
We may allude here to the little moths, described by Westwood under the name of Epipyrops,[[294]] that have the extraordinary habit of living on the bodies of live Homopterous Insects of the family Fulgoridae in India. What their nutriment may be is not known. The larva exudes a white flocculent matter, which becomes a considerable mass, in the midst of which the caterpillar changes to a pupa. Westwood placed the Insect in Arctiidae; Sir George Hampson suggests it may be a Limacodid, and this appears probable.
Fam. 27. Megalopygidae (or Lagoidae).—The American genera, Megalopyge and Lagoa, are treated by Berg and by Packard[[295]] as a distinct family intermediate between Saturniidae and Limacodidae. The larva is said by the latter authority to have seven pairs of abdominal feet instead of five pairs—the usual number in Lepidoptera. When young the caterpillars of Lagoa opercularis are white and resemble a flock of cotton wool. When full grown the larva presents the singular appearance of a lock of hair, moving in a gliding, slug-like manner. Under the long silky hair there are short, stiff, poison-hairs. The larva forms a cocoon, fitted with a hinged trap-door for the escape of the future moth. This curious larva is destroyed by both Dipterous and Hymenopterous parasites.
Fam. 28. Thyrididae.—A small family of Pyraloid moths, exhibiting considerable variety of form and colour, frequently with hyaline patches on the wings. They are mostly small Insects, and contain no very striking forms. Some of them look like Geometrids of various groups. The family is widely distributed in the tropical zone, and includes 25 genera, of which Rhodoneura, with upwards of 100 species, is the chief one. The larvae are said to be similar to those of Pyralidae. This family is considered by Hampson and Meyrick to be ancestral to butterflies.[[296]]
Fig. 201.—Lappet-moth, Gastropacha quercifolia, ♀. Britain.