The family Prodoxidae consists of some Tineids, the larvae of which feed in the pods and stems of the Yuccas of south-western North America; they have the mouth of very unusual form (Fig. 208, E), and some of them, by aid of this peculiar mouth, exhibit a remarkable modification of instinct. The facts are chiefly known from the observations of Riley[[337]] on Pronuba yuccasella, a moth living on Yucca filamentosa; this plant has been introduced into our gardens in this country, where it never, we believe, produces seed. The Yuccas are not fitted for self-fertilisation or for fertilisation by Insect agency of an ordinary kind. The progeny of the moth develops in the pods of the plant, and as these cannot grow until the flowers have been fertilised, the moth has the habit of fertilising the flowers at the time she lays her egg in the part that is to develop into the pod, and to be the food for her own progeny. The female moth first visits the stamens, and collects, by the aid of the maxillae (which in this sex are very remarkably formed),[[338]] a considerable mass of pollen, which she holds by means of the peculiar maxillary tentacles; she then lays an egg in the pistil, usually of some flower other than that from which she has gathered the pollen; and after she has accomplished this act she carefully applies the pollen she had previously collected to the pistil, so as to secure the fertilisation of the flower and the development of the pod.
The species of Prodoxus stand in a very peculiar relation to Pronuba. They also live in Yuccas, and have habits similar to those of Pronuba, with the important exception that, being destitute of the requisite apparatus, they do not fertilise the Yucca-flowers, and are thus dependent on Pronuba for the steps being taken that are necessary for the rearing of the progeny of the two kinds of moth. Hence the name of Yucca-moth has been bestowed on Pronuba, and that of "bogus Yucca-moth" on the Prodoxus. The Pronuba we figure is the largest and most remarkable species of the genus and fertilises Yucca brevifolia; the larva is destitute of abdominal feet, and in the pupa the spines on the back that exist in nearly all pupae that live in stems are developed to an extraordinary extent. The Yuccas do not flower every year, and the Prodoxidae have a corresponding uncertainty as to their periods of appearance, passing sometimes a year or two longer than usual in the pupal stage.
Fam. 46. Eriocephalidae.—This family has recently been proposed for some of the moths formerly included in the genus Micropteryx.[[339]] They are small, brilliant, metallic Insects, of diurnal habits, but are very rarely seen on the wing, and it is doubtful whether they can fly much. These little Insects are of peculiar interest, inasmuch as they differ from the great majority of the Lepidoptera in at least two very important points, viz. the structure of the wings and of the mouth-parts. The mouth shows that we may consider that the Lepidoptera belong to the mandibulate Insects, although in the great majority of them the mandibles in the final instar are insignificant, functionless structures, or are entirely absent, and although the maxillae are so highly adapted for the tasting of sweets that it is difficult to recognise in them the parts usually found in the maxilla of mandibulate Insects.
Fig. 209.—Larva of Eriocephala calthella. (After Chapman.) A, Young larva from side, × 50; B, portion of skin with a bulla or ball-like appendage: C, abdominal foot of larva.
Eriocephala in both these respects connects the Lepidoptera with Mandibulata: the mandibles have been shown by Walter[[340]] to be fairly well developed; and the maxillae are not developed into a proboscis, but have each two separate, differentiated—not elongated—lobes, and an elongate, five-jointed, very flexible palpus. The moths feed on pollen, and use their maxillae for the purpose, somewhat in the style we have mentioned in Prodoxidae. The wings have no frenulum, neither have they any shoulder, and they probably function as separate organs instead of as a united pair on each side: the modification of the anterior parts of the hind wing—whereby this wing is reduced as a flying agent to the condition of a subordinate to the front wing—does not here exist: the hind wing differs little from the front wing in consequence of the parts in front of the cell being well developed. There is a small jugum. These characters have led Packard to suggest that the Eriocephalidae should be separated from all other Lepidoptera to form a distinct sub-Order, Lepidoptera Laciniata.[[341]] The wing-characters of Eriocephala are repeated—as to their main features—in Hepialidae and Micropterygidae; but both these groups differ from Eriocephala as to the structure of the mouth-parts, and in their metamorphoses. Although Eriocephala calthella is one of our most abundant moths, occurring in the spring nearly everywhere, and being easily found on account of its habit of sitting in buttercup-flowers, yet its metamorphoses were till recently completely unknown. Dr. Chapman has, however, been able to give us some information as to the habits and structure of the larvae, in both of which points the creature is most interesting. The eggs and young larvae are "quite unlike our ideas of a Lepidopterous Insect;" the former have a snowy or mealy appearance, owing to a close coating of minute rods standing vertically on the surface of the egg, and often tipped with a small bulb. The larva lives amongst wet moss and feeds on the growing parts thereof; it is not very similar to any other Lepidopterous larva: Dr. Chapman suggests a similarity to the Slug-worms (Limacodids), but Dyar is probably correct in thinking the resemblances between the two are unimportant: the larva of Eriocephala possesses three pairs of thoracic legs, and eight pairs of abdominal appendages, placed on the segments immediately following the thorax; on the under-surface of the ninth and tenth abdominal segments there is a sucker, trifoliate in form; this is probably really situate entirely on the tenth segment: the body bears rows of ball-appendages, and the integument is beautifully sculptured. The head is retractile and the antennae are longer than is usual in caterpillars. This larva is profoundly different from other Lepidopterous larvae inasmuch as the abdominal feet, or appendages, are placed on different segments to what is customary, and are of a different form. Unfortunately the pupa has not been procured, but there is some reason for supposing that it will prove to be more like that of Tineidae than like that of Micropterygidae.
The New Zealand genus Palaeomicra is only imperfectly known. Meyrick considers it the "most ancient" Lepidopteron yet discovered; and it would appear that its relations are with Eriocephala rather than with Micropteryx. From information he has kindly given to us, we are able to say that this moth possesses mandibles but no proboscis.
Fig. 210—Larva of Micropteryx sp. A, Ventral view of the larva, magnified; B, the same, with setae unduly magnified. Britain.
Fam. 47. Micropterygidae.—Small moths of metallic colours, without mandibles, with elongate maxillary palpi: without frenulum: both wings with a complex system of wing-veins: on the hind wings the area anterior to the cell is large, and traversed by three or four elongate, parallel veins.