In South America there is a somewhat peculiar genus of Nymphalides—Ageronia—that delights in settling on the trunks of trees rather than on flowers or leaves. It was long since noticed that the the species of Ageronia make a clicking noise; in some cases when on the wing, in other cases by moving the wings when the Insect is settled. The object of the noise is quite uncertain; it has been suggested that it is done in rivalry or courtship, or to frighten away enemies. Bigg-Wether found, however, that in South Brazil there is a lazy little bird to which this sound serves as a signal, inducing it to descend from its perch and eat the clicker. The mode in which the noise is produced is not quite clear. Sir George Hampson has pointed out[[223]] that the fore wing bears at the extreme base a small appendage bearing two hooks, and that two other processes on the thorax play on these when the wing moves. His suggestion that these hooks are the source of the sound seems highly probable.
There is a great variety in the larvae of Nymphalides. In the Vanessa group the body is armed with spines, each one of which bears shorter thorns, the head being unadorned. The Fritillaries (Argynnis, Melitaea) also have caterpillars of this kind. In many other forms the head itself is armed with horns or spines of diverse, and frequently remarkable, character. In Apatura and its allies the body is without armature, but the head is perpendicular, the vertex bifid and more or less prolonged. The caterpillar of our Purple Emperor, Apatura iris, is quite unlike any other British caterpillar; in colour it is like a Sphingid larva—green with oblique lateral stripes of yellow and red—but in form it is slug-like, pointed behind, and it has on the head two rather long tentacle-like horns. In the South American genus Prepona, the larva of which in general form resembles that of Apatura there are no anal claspers, but the extremity of the body is prolonged, forming a sort of tail.
Fam. 2. Erycinidae (Lemoniidae of some authors).—The female has six perfectly formed legs, though the front pair is smaller. The male has the coxae of the front legs forming a spine, and the tarsi unjointed, without claws. This family consists of about 1000 species, usually of rather small size, exhibiting a great variety of shape and coloration, some of them being remarkably similar to some of the gay, diurnal moths of South America. The palpi are usually small, but in Ourocnemis they are large and porrect. The family is specially characteristic of tropical America, but there is one small group of 30 or 40 species, Nemeobiides, in the Eastern Hemisphere. We have one species in Britain, Nemeobius lucina, the Duke of Burgundy Fritillary. Neither the larvae nor the pupae of Erycinidae present any well-marked characteristic feature, but exhibit considerable variety. According to Bar,[[224]] some of the larvae are like those of moths; the caterpillar of Meliboeus is said to be like that of a Liparis: the chrysalis has the short, rounded form of that of the Lycaenidae, and is suspended with the head down, and without a band round the body. The larvae of Eurygona are gregarious. The pupae of some other forms adhere, heads downwards, to branches. Scudder considers that this family is not distinct from Lycaenidae, and that the Central American genus Eumaeus connects the two. Reuter also treats Erycinidae as a division of Lycaenidae.
Sub-Fam. 1. Erycinides.—[Characters of the family.] Palpi not unusually large. We place all the Erycinidae in this sub-family except the following—
Sub-Fam. 2. Libytheides.—Butterflies of average size, with the palpi large and porrect: the front legs of the male small, the tarsus reduced to one joint: the front leg of the female of the normal structure, and but little reduced in size. This division consists of the single genus Libythea, with only a score of species. They are Insects somewhat like Vanessa in appearance, but cannot fail to be recognised on account of the peculiar palpi. The genus is of very wide distribution, occurring in most parts of the warm and temperate continental regions, and it also occurs in Mauritius and the Antilles.
The Libytheides have given rise to much difference of opinion amongst systematists, some of whom assign them as a sub-family to the Erycinidae, some to the Nymphalidae; while others treat them as a family apart. The families Nymphalidae, Erycinidae and Lycaenidae are so intimately allied, that Scudder is probably correct in considering them to form really one huge family; if this view were adopted there would be no difficulty in locating Libythea therein. If they be kept apart, it is almost necessary to separate Libythea also; though possibly its claims to be placed in Erycinidae slightly preponderate. The recently described genus Ourocnemis to some extent connects Erycinides with Libythaeides.[[225]]
Fam. 3. Lycaenidae.—The front legs but little smaller than the others: in the male, however, the tarsus, though elongate, is only of one joint, and is terminated by a single claw. No pad on the front tibia. Claws not toothed. The Lycaenidae, or Blues, are, as a rule, of small size, but in the tropics there are many that reach the average size of butterflies, i.e. something about the stature of the Tortoise-shell butterfly. The family is one of the larger of the divisions of butterflies, considerably more than 2000 species being at present known, and this number is still rapidly increasing. Although blue on a part of the upper surface is a very common feature in the group, it is by no means universal, for there are many "Coppers," as well as yellow and white Lycaenidae. Many species have delicate, flimsy appendages—tails—to the hind wings, but in many others these are quite absent; and there are even tailed and tailless forms of the same species. The members of the group Lipteninae (Liptena, Vanessula, Mimacraea, etc.) resemble members of other sub-families of Nymphalidae, and even of Pieridae. Lycaenidae are well represented wherever there are butterflies; in Britain we have 18 species.
The larvae of this family are very peculiar, being short, thicker in the middle, and destitute of the armature of spines so remarkable in many other caterpillars. It has of late years been frequently recorded that some of these larvae are attended by ants, which use their antennae to stroke the caterpillars and induce them to yield a fluid of which the ants are fond. Guénée had previously called attention[[226]] to the existence of peculiar structures contained in small cavities on the posterior part of the caterpillar of Lycaena baetica. These structures can be evaginated, and, it is believed, secrete a fluid; Edwards and M‘Cook are of opinion that they are the source of the matter coveted by the ants. The larvae are without spines.
The caterpillars of the Blues have some of them strange tastes; more than one has been recorded as habitually feeding on Aphidae and scale-Insects. The pupae are, like the larvae, of short inflated form. By a remarkable coincidence, the pupae of two species bear a considerable resemblance to the heads of monkeys, or mummies. The Lycaenid pupa is usually extremely consolidated, destitute of movement, and is supported—in addition to the attachment by the cremaster—by a silk thread girdling the middle. There are exceptions to these rules, and according to Mr. Robson the pupa of Tajuria diaeus hangs free, suspended from a leaf, and can move the body at the spot where the abdominal segments meet the wing-cases in the dorsal line.[[227]]
Fam. 4. Pieridae.—The six legs well developed, and similar in the sexes; there is no pad on the front tibia. The claws of all the feet are bifid, or toothed, and there is an empodium. There are upwards of 1000 species of Pieridae already known. Although several taxonomists treat the Pieridae and Papilionidae as only subdivisions of one family, yet they appear to be quite distinct, and the relationships of the former to be rather with Lycaenidae. In Pieridae, white, yellow, and red are the predominant colours, though there is much black also. It has recently been ascertained that the yellow and red pigments, as well as the white, are uric acid or derivatives therefrom.[[228]] The physiology of this peculiarity has not yet been elucidated, so that we do not know whether it may be connected with some state of the Malpighian vessels during metamorphosis.