Cicadidae are almost confined to the warmer regions of the earth, but we have one species, a great rarity, in the extreme south of England; altogether there are about 800 species known. These Insects are seen above ground—so far as the life-histories are at present known—only in the perfect condition, the creatures in their earlier stages being subterranean and living on roots. As soon as the individual comes out of the ground it splits open the nymph-skin, and the perfect Cicada emerges. One species—the North American Cicada septendecim—is a most notorious Insect owing to its life-cycle of seventeen years. It is considered that the individual, after nearly seventeen years of underground existence, comes to the surface and lives for a brief period the life of a noisy Insect. This is the only Insect at present known having so considerable a longevity. This fact, and several other peculiarities, have attracted much attention, so that there is an extensive literature connected with the seventeen-year Cicada. It has a wide distribution over the United States, but does not confine its appearance to every seventeenth year, being found somewhere or other—frequently in numerous localities—almost every year. The evidence as to its periodicity has been obtained by taking the locality and other points into consideration as well as the year of appearance. By so doing it has been found possible to establish the existence of twenty-two broods which are distinguished by consecutive numeration. This being done, the evidence as to the years during which Cicadas have appeared in any given locality is examined, and the result is believed to bear out the view that the life-cycle of the individual Insect is really one of seventeen years. According to this view there are, underground, in certain localities individuals of different ages that will appear on the surface as mature individuals in different years. Thus in 1885 it was understood that there were underground in Alabama two broods, viz. brood xviii. that would appear on the surface in 1894, and brood iv. that would appear on the surface in 1896. The predictions made as to the years in which Cicadas would appear in some given locality are considered to have proved correct. Moreover, particular entomologists have in certain localities verified by personal examination the appearance of the Insects for several consecutive periods of seventeen years. These facts appear fairly conclusive, but they are much complicated by another point, viz. that in certain localities the period is one of thirteen, not of seventeen, years. This is to some extent a question of climate, the thirteen-year interval being chiefly characteristic of the Southern States. It is not, however, entirely so, for there are localities in which the broods have an interval of either thirteen years or seventeen years. Another fact should be remembered, viz. that it is admitted that not quite all the individuals of a particular brood are true to their proper time of appearance; in other words, a few specimens may appear precociously a year or two before their comrades, while some may lag behind to a considerable extent. It is therefore a matter for great surprise that, under these circumstances, the broods should keep distinct at all, for one would suppose that time-variation of this kind would lead to completely obscuring the distinctness of the broods. We must also call attention to the fact that both the seventeen-year and the thirteen-year broods have a dimorphic form, or sub-species, called C. cassinii which accompanies the ordinary form, with which it is apparently as a rule not connected by intermediates.[[502]]
Cicadidae are provided with powerful ovipositors. The eggs of C. septendecim are deposited in the woody stems of bushes; after remaining there a few weeks the young hatch out, drop to the ground, and, as previously stated, disappear for nearly seventeen years, nearly the whole of which time is passed in the larval state, the nymph-condition existing for only a few days. They feed on the roots of various trees; it has been said that they are injurious in this way, but other authorities maintain that they suck only a moist exudation from the roots. It is very difficult to obtain information as to their strange, prolonged, subterranean life; it said that the Insects sometimes penetrate to a great depth—ten feet, even twenty feet are mentioned;—and as great changes may take place on the surface during their long lives, these Insect Rip Van Winkles sometimes emerge in very strange conditions, and may appear even in deep cellars. When the pupa comes to the surface it hooks itself on to the stem of some plant or other object, the skin of the back splits, and the Cicada emerges. Among the inexplicable peculiarities of this Insect must be mentioned the fact that when emerging it sometimes constructs chimneys, or flues, extending several inches above the surface of the ground. The reason for this is much disputed; it was said that they are for refuge against inundations, but this appears to be very doubtful. Certain of the broods consist of an almost incalculable number of individuals, and it is very strange to hear woods, or other localities, that have been for many years free from these Insects, all at once resounding with their noisy song. The seventeen-year Cicada is considered to be doomed to a speedy extinction; the extension of cultivation and building, and the introduction to America of the English sparrow, are likely to prove too much for the Insect.
Although Hemiptera are classified by many among the Ametabola or Insects without metamorphosis, it is impossible to deny that the Cicadidae exhibit a considerable amount of metamorphosis, and they are usually mentioned as exceptional. The young (Fig. 280, A) is totally unlike the adult in form and colour, and maintains, to a certain extent, its existence by the aid of a different set of implements. The larva of the Cicada is colourless, with an integument of very feeble consistence, rather large antennae, and a remarkable pair of fossorial legs; the wings are totally wanting. The mode of passage from the larval to the pupal state has not been recorded. The pupa, or nymph, differs from the larva by its much shorter, compressed form; by being encased in a remarkably hard shell; and by the antennae approximating in form to those of the adult. It has short wing-pads at the sides of the body; the front legs are remarkably powerful, and the creature is capable of moving about; the imago escapes from the pupa by the splitting dorsally of the middle of the thoracic segments. The empty pupa-skin does not shrivel, but retains its form, and in countries where Cicadas occur, frequently attracts attention by the strange form it presents, being often placed in a conspicuous position.
Song.—Cicadas are the most noisy of the Insect world; the shrilling of grasshoppers and even of crickets being insignificant in comparison with the voice of Cicada. Darwin heard them in South America when the Beagle was anchored a quarter of a mile from the shore; and Tympanoterpes gigas, from the same region, is said to make a noise equal to the whistle of a locomotive.[[503]] A curious difference of opinion prevails as to whether their song is agreeable or not; in some countries they are kept in cages, while in others they are considered a nuisance. The Greeks are said to have decided in favour of their performances, the Latins against them. Only the males sing, the females being completely dumb; this has given rise to a saying by a Greek poet (so often repeated that it bids fair to become immortal) "Happy the Cicadas' lives, for they all have voiceless wives."[[504]] The writer considers the songs of the European species he has heard far from unpleasant, but he is an entomologist, and therefore favourably prepossessed; and he admits that Riley's description of the performances of the seventeen-year Cicada is far from a satisfactory testimonial to the good taste of that Insect; Riley says, "The general noise, on approaching the infested woods, is a combination of that of a distant threshing-machine and a distant frog-pond. That which they make when disturbed, mimics a nest of young snakes or young birds under similar circumstances—a sort of scream. They can also produce a chirp somewhat like that of a cricket and a very loud, shrill screech prolonged for fifteen or twenty seconds, and gradually increasing in force and then decreasing." The object, or use of the noise is very doubtful; it is said that it attracts the females to the males. "De gustibus non est disputandum!" perhaps, however, there may be some tender notes that we fail to perceive; and it may be that the absence of any definite organs of hearing reduces the result of a steam-engine whistle to the equivalent of an agreeable whisper. No special auditory organs have been detected[[505]] as we have already intimated; and certain naturalists, amongst whom we may mention Giard, think that the Insects do not hear in our sense of the word, but feel rhythmical vibrations; it is also recorded that though very shy the Insects may be induced to approach any one who will stand still and clap his hands—in good measure—within the range of their sensibilities. There is a good deal of support to the idea that the males sing in rivalry.
Vocal structures.—Although we may not be able to pronounce a final opinion as to the value to the Insect of the sounds, yet we cannot withhold our admiration from the structures from which they proceed. These are indeed so complex that they must be ranked as amongst the most remarkable voice-organs in the animal kingdom. They are totally different from the stridulating organs that are found in many other Insects, and are indeed quite peculiar to the Cicadidae. Some difference of opinion has existed as to the manner in which the structures act, but the account given by Carlet, some of whose figures we reproduce, will, we believe, be found to be essentially correct. The structures are partly thoracic and partly abdominal. On examining a male Cicada there will be seen on the under surface two plates—the opercula—usually meeting in the middle line of the body and overlapping the base of the abdomen to a greater or less extent according to the species, sometimes nearly covering this part of the body; these are enlargements of the metathoracic epimera; they can be slightly moved away from the abdomen, and, as the latter part is capable of a still greater extent of movement, a wide fissure may be produced, displaying the complex structures. In order to see the parts it is better to cut away an operculum; underneath it three membranes can be seen, an external, the timbal; an anterior, the folded or soft membrane; and a posterior, the mirror. This last is a most beautiful object, tensely stretched and pellucid, yet reflecting light so as to be of varied colours; there are also three stigmata, and some chambers connected with the apparatus. The sound is primarily produced by the vibrations of the timbal, to which a muscle is attached; the other membranes are probably also thrown into a condition of vibration, and the whole skeleton of the Insect helps to increase or modify the sound, which is probably also influenced by the position of the opercula. The stigmata probably play an important part by regulating the tension of the air in the chambers. In the female some of the structures are present in a rudimentary form, but there are no muscles, and this sex appears to be really quite voiceless.
Fig. 281.—Musical apparatus of Cicada plebeia. (After Carlet.) A, Ventral view (Operculum on right side is removed); ap, apophysis; C, cavern; c, trochantin (cheville of Réaumur); ent, part of internal skeleton of abdomen; mi, specular membrane; m.pl, soft or folded membrane; P, base of leg; st, st′, st″, stigmata; t, drum "timbale"; v, operculum; 1a, first, 2a, second abdominal segment: B, same seen laterally, portion of abdominal wall as well as operculum removed; A, point of insertion of hind wing; Mes, mesothorax; sc, scutum of metathorax; 3a, third abdominal segment; rest as in A.
Fam. 2. Fulgoridae.—Ocelli two (rarely three, or entirely obsolete), placed beneath the eyes or near the eyes, usually in cavities of the cheeks, antennae placed beneath the eyes, very variable in form; usually of two joints terminated by a very fine hair, the second joint with a peculiar texture of the surface, owing to the existence of sensitive structures (Hansen). Form of head very diverse; vertex and face forming either a continuous curve, or the planes of the vertex and face forming an acute angle, or both prolonged so as to form a projection or growth that may be monstrous. Prothorax neither armed nor unusually developed.
Fig. 282—Fulgora candelaria. × 1. China.