The mode in which leaves and shoots are twisted and rolled by the very small larvae has been much discussed and is probably the result of two or three distinct causes:—1, the immediate operations of the larva; 2, the contraction of silk when drying; 3, changes in the mode of growth of the parts of the vegetable, resulting from the interference of the caterpillar. The larvae of this family that live in fruits are only too widely (we will not say well) known. Stainton gives as the habitat of Epinotia funebrana, "larva frequent in plum-pies"; the caterpillar of Carpocapsa pomonella (the Codling-moth) mines in apples and pears, and its ravages are known only too well in widely distant parts of the world where fruit-trees of this kind are cultivated. C. splendana lives in acorns and walnuts; C. juliana in Spanish chestnuts. Two, if not more, larvae live in the seeds of Euphorbiaceous plants, and have become notorious under the name of jumping-beans, on account of the movements they cause. As these latter show no trace externally of being inhabited, the movements are supposed to be a mysterious property of the seed; they are really due to its containing a large cavity, extending, in one direction of the seed, nearly or quite from skin to skin; in this the larva makes a movement sufficient to alter the point of equilibrium of the quiescent seed, or as a free body to strike some part of it. The exact nature of the movements of the larva have not, we believe, been ascertained. There are, at least, two species of these Insects, and two plants harbouring them, known in the United States and Mexico, viz. Carpocapsa saltitans living in the seeds of Croton colliguaja and Grapholitha sebastianiae living in the seeds of Sebastiania bicapsularis.
Fam. 45. Tineidae.—Small moths with the labial palpi more flexible and mobile than in other moths; usually separated and pointed. Hind wings frequently with very long fringes, the wing itself being proportionally reduced in size, and in consequence pointed at the tip. Larvae very diverse, almost always with habits of concealment. The series of forms included under this head is very numerous, the British species alone mounting up to 700, while the total described cannot be less than 4000. This number, however, must be but a fragment of what exists, if Mr. Meyrick be correct in supposing that a single one of the divisions of the family—Oecophoridae—comprises 2000 species in Australia and New Zealand alone.
Fig. 207—Diplosara lignivora (Gelechiides). Hawaiian Islands.
As the study of these Insects is attended with great difficulty on account of their fragility and the minute size of the great majority, it is not a matter for surprise that their classification is in a comparatively rudimentary state. We shall not, therefore, deal with it here. Neither can we attempt to give any idea of the extreme diversity in the colours, forms, and attitudes of these small Insects. The one shown in Fig. 207, is remarkable on account of the great accumulation of scales on the wings and legs. As regards the pointed wings and the long fringes, we may remark that it is probable that in many of these small forms the wings are passive agents in locomotion; a similar condition of the wings is found in other very minute Insects, e.g. Thysanoptera and Trichopterygidae; in all these cases the framework of the wings is nearly absent: in some forms of the Tineidae, Opostega, e.g. the nervules are reduced to three or four in each wing. The variety in habits is as great as that of the external form, and the larvae exceed in diversity those of any other group of Lepidoptera. No doubt a corresponding amount of diversity will be discovered in the details of structure of the perfect Insects, the anatomy of but few having been at present investigated. Tinea pellionella has two very important peculiarities in its internal anatomy: the testes consist of four round follicles on each side, and, contrary to the condition generally prevalent in Lepidoptera, are not brought together in a common capsule: the two groups are, however, not quite free (as they are in Hepialus), but are connected by a loose tracheal network. Even more remarkable is the fact also pointed out by Cholodkovsky[[332]] that the adult Insect possesses only two Malpighian tubes instead of six, the normal number in Lepidoptera; in the larva there are, however, six elongate tubes. The group of forms to which Tinea belongs is remarkable for the diversity and exceptional character of the food-habits of the larvae; species subsist on dried camel's dung, various kinds of clothes, furs, and hair, and even about horns of deer and horses' hoofs: one species has been found in abundance in the hair of a live sloth, Bradypus cuculliger, under circumstances that render it possible that the larva feeds on the creature's hair, though it may feed on minute vegetable matter found in the hair. The larva of Tinea vastella is occasionally found feeding on the horns of living antelopes. Several species of Tineidae are known to devour Scale-Insects.
Lita solanella is notorious for the ravages it commits on stored potatoes. Quite a number of species live on cryptogamic matter, or in old wood; Oinophila v-flavum feeds on the mould on the walls of cellars, and is reputed to be injurious by occasionally also attacking the corks of bottles containing wine. Oecocecis guyonella is said to be the cause of galls on Limoniastrum guyonianum, a plant that, growing in the deserts to the south of Algeria, is a favourite food of camels, and is frequently entirely covered with sand. The deposition of an egg by this moth is believed by Guénée[[333]] to give rise to a gall in which the larva is entirely enclosed (like the larvae of the gall-flies). Of Clothes-moths there are at least three species widely distributed. Trichophaga tapetzella is perhaps entitled to be considered the Clothes-moth; its caterpillar not only feeds on clothes, but spins webs and galleries amongst them. Tinea pellionella is also very common; its larva lives in a portable case, while that of the third species, Tineola biselliella, forms neither a case nor definite galleries. We have found this the most destructive of the three at Cambridge. Clothes or valuable furs may be completely protected by wrapping them in good sound paper in such a way that no crevices are left at the places where the edges of the paper meet. Garments that have become infested may be entirely cleared by free exposure to air and sunshine.
Two species of Tinea have been recorded as viviparous, viz. Tinea vivipara in Australia, and an undetermined species in South America. The species of the genus Solenobia—in which the female is apterous—are frequently parthenogenetic. The group Taleporiidae, to which this genus belongs, is by some classified with Psychidae, in which family, as we have pointed out, one or two parthenogenetic forms are also known.
The larvae of Tineidae, though they do not exhibit the remarkable armature found in so many of the larger caterpillars, are exceedingly diverse.[[334]] Some are entirely destitute of feet (Phyllocnistis). Others are destitute of the thoracic legs; Nepticula is in this case, but it is provided with an increased number of abdominal feet, in the form of more or less imperfect ventral processes. Some mine in leaves, others live in portable cases of various forms. Some are leaf-miners during their early life, and subsequently change their habits by constructing a portable case. The genus Coleophora affords numerous instances of this mode of life; the habits of these case-bearers exhibit considerable variety, and there are many points of interest in their life-histories. Change of habit during the larval life has already been alluded to as occurring in many Lepidoptera and is nowhere more strikingly exemplified than in certain Tineidae. Meyrick mentions the following case as occurring in an Australian Insect, Nematobola orthotricha;[[335]] the larva, until two-thirds grown, is without feet, and is almost colourless, and mines in the leaves of Persoonia lanceolata; but when two-thirds grown it acquires sixteen feet, changes colour, becoming very variegate, and feeds externally, unprotected, on the leaves. The cases of the case-bearing Tineids are usually of small size, and do not attract attention like those of Psychidae. A very remarkable one was discovered by Mr. E. E. Green in Ceylon, and was at first believed to be formed by a Caddis-worm. It has now been ascertained that the Insect forming it is the caterpillar of Pseudodoxia limulus, a Tineid moth of the group Depressariidae;[[336]] the case is composed of minute fragments of moss, sand, and lichens; the anterior end is dilated into a shield-like hood that covers and protects the anterior parts of the larva when feeding; the food is mosses and lichens on rocks and trees. Before pupating, the larva folds down the edges of the hood over the mouth of the tube, like an envelope, fastening them with silk. The case is fixed to the rock or other support and hangs there until the moth appears.
Fig. 208—Pronuba synthetica. North America. A, Larva; B, C, pupa, ventral and lateral aspects; D, female moth; E, head and part of thorax of the female moth: a, labial palp; b, maxillary tentacle; c, maxillary palp; d, proboscis; e, base of front leg. (After Riley.)