The females have no wings, while the males have them, and possess very well-developed elytra. The females resemble the larvæ much, only they have the head more conspicuous, and the thorax buckler-shaped, like the male. The larvæ feed on small molluscs, hiding in the snails' shells, after having devoured the inhabitant. They also possess the phosphorescent property in a less degree than the adult females. The female pupa resembles the larva; the pupa of the male, on the contrary, has the wings folded back under a thin skin. The perfect insect appears towards the autumn.
The Glow-worm (Lampyris noctiluca, [Fig. 550]) is of a brownish yellow. It is common in England. In a kindred species, the Luciola Italica, the two sexes are winged, of a tawny-brown, and equally phosphorescent. They are met with in great numbers in Italy, and the lawns are covered with them. Other insects of this family are without the faculty of emitting light; as, for example, the genus Lycus, of brilliant colours, which are met with in Africa and India. One of the finest is the Lycus latissimus.
Drilus is another genus, comprising insects of very singular habits. The type is the Drilus flavescens. The male—a quarter of an inch long, black and hairy, with elytra of a testaceous yellow, and with pectinated antennæ—for a long time was alone known. The female—from ten to fifteen times as large, without wings and elytra, of a yellowish brown—was not discovered till much later, having apparently nothing in common with the male in shape or colour. The metamorphoses of these curious insects are now perfectly understood. Mielzinsky, a Polish naturalist established at Geneva, found the Drilus in the larva state in the shell of the Helix nemoralis. These larvæ devour the snail whose dwelling they occupy, as do the larvæ of the Lampyris. Mielzinsky saw them emerge, but obtained only females, which differed scarcely at all from the larvæ from which they proceeded. He made a separate genus of them, under the denomination of Cochleoctonus, and called the species Vorax. Later, Desmarest resumed these observations. He provided himself, at the Veterinary College of Alfort, with a number of shells of the Helix filled with the same larvæ. He saw come out of them, not only Cochleoctoni, but also Drili, and he watched their coupling. It was then proved, by this unanswerable argument, that these two insects, so unlike each other, belong to the same species.
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| Fig. 552.—Jumping organ of the Elater, seen sideways. | ||
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| Fig. 551.—Jumping organ of the Elater. | Fig. 553.—Larva of the Elater. |
The larva of the Drilus flavescens fixes itself upon the shell of the snail by a sort of sucker, like a leech. Little by little it slips in between the mollusc and its house, and devours it entirely. To change into a pupa, it shuts up the entrance to the shell with its old skin; and when arrived at the perfect state, quits the shell which served it as a temporary dwelling. The females of the Drilus flavescens take refuge under stones and dry leaves, or crawl slowly along the ground; whilst the males, which fly with great ease, are on the plants and brushwood. These insects are not rare in the environs of Paris. M. H. Lucas has observed, in Algeria, near to Oran, another curious species, the Drilus Mauritanicus. The larva of this insect lives at the expense of the animal of the Cyclostoma Volzianum, which closes the entrance to its shell with a covering of some calcareous substance. It fixes itself on the edge of the shell, with the aid of its sucker, and directs its strong mandibles to the side on which the snail is obliged to raise the covering, either to breathe the air or to walk. In this position it has the patience to wait for many days at the door. The snail puts off for as long a time as he is able the fatal moment. But when, overcome by hunger or nearly stifled in his prison, he decides at last to open the door, the Drilus profits immediately by this opportunity, and cuts the muscle which keeps back the foot of the snail. The breach being made, nothing more opposes itself to the entrance of the enemy. He slips in, and sets to work to eat at his leisure the unfortunate inoffensive mollusc, which affords him board and lodging. The Ptilodadylides, the Eucinetides, and the Cebrionides belong to the same family. The first is exotic.
The Elateridæ are rather large insects, often of hard texture, having the prosternum prolonged into a point (Figs. [551] and [552]), and the antennæ indented saw-wise. They have the power of jumping when placed on their backs, and of alighting again on their legs. Hence their name of Elater (derived from the same root as the word elastic). They produce, in leaping, one sharp rap, and often knock many raps when they are prevented from projecting themselves. This is the mechanism which permits the skip-jack to execute these movements. It bends itself upwards by resting on the ground by its head and the extremity of the abdomen, and then it unbends itself suddenly, like a spring. The point at the end of the thorax penetrates into a hollow of the next ring; the back then strikes with force against the plane on which it rests, and the animal is projected into the air. It repeats this manœuvre till it finds itself on its belly, for its legs are too short to allow of its turning over. Its structure supplies it with the means and the strength of rebounding as many times as it falls on its back, and it can thus raise itself more than twelve times the length of its body.
The larvæ of the genus Elateridæ ([Fig. 553]) are cylindrical, with a scaly skin and very short legs. They live in rotten wood or in the roots of plants. According to M. Goureau, they pass five years in this state.
The larvæ of the genus Agriotes occasion considerable damage to wheat-fields. They have much resemblance to the meal-worm, or larva of the Tenebrio. The Tetralobides are the largest of the Elateridæ, attaining to a length of two inches; and are inhabitants of Africa and Australia.
In America are found phosphorescent Elateridæ. These are the Pyrophori, which the Spaniards of South America call by the name of Cucuyos. They have, at the base of their thorax, two small, smooth, and brilliant spots, which sparkle during the night; the rings of the abdomen also emit a light. They give light sufficient to enable one to read at a little distance from them. The Pyrophorus noctilucus ([Fig. 554]) is very common in Havannah, in Brazil, in Guyana, in Mexico, &c., and may be seen at night in great numbers, amongst the foliage of trees. At the time of the Spanish conquest, a battalion, just disembarked, did not dare to engage with the natives, because it took the Cucuyos which were shining on the neighbouring trees for the matches of the arquebuses ready to fire. "In these countries," says M. Michelet, "one travels much by night, to escape the heat. But one would not dare to plunge into the peopled shades of the deep forests if these insects did not reassure the traveller. He sees them shining afar off, dancing, twisting about; he sees them near at hand on the bushes by his side; he takes them with him; he fixes them on his boots, so that they may show him his road and put to flight the serpents; but when the sun rises, gratefully and carefully he places them on a shrub, and restores them to their amorous occupations. It is a beautiful Indian proverb that says, 'Carry away the fire-fly, but restore it from whence thou tookest it'" [127] The Creole women make use of the Cucuyos to increase the splendour of their toilettes. Strange jewels! which must be fed, which must be bathed twice a day, and must be incessantly taken care of, to prevent them from dying. The Indians catch these insects by balancing hot coals in the air, at the end of a stick, to attract them, which proves that the light which these insects diffuse is to attract. Once in the hands of the women, the Cucuyos are shut up in little cages of very fine wire, and fed on fragments of sugar-cane. When the Mexican ladies wish to adorn themselves with these living diamonds, they place them in little bags of light tulle, which they arrange with taste on their skirts. There is another way of mounting the Cucuyos. They pass a pin, without hurting them, under the thorax, and stick this pin in their hair. The refinement of elegance consists in combining with the Cucuyos, humming-birds and real diamonds, which produce a dazzling head-dress. Sometimes, imprisoning these animated flames in gauze, the graceful Mexican women twist them into ardent necklaces, or else roll them round their waists, like a fiery girdle. They go to the ball under a diadem of living topazes, of animated emeralds, and this diadem blazes or pales according as the insect is fresh or fatigued. When they return home, after the soirée, they make them take a bath, which refreshes them, and put them back again into the cage, which sheds during the whole night a soft light in the chamber. In 1766, a Cucuyo, brought alive from America to Paris, probably in some old piece of wood which happened to be on the vessel, caused great terror to the inhabitants of the Faubourg St. Antoine, when they saw it flying in the evening, glittering in the air. In 1864 a number of Cucuyos were brought from Mexico to Paris by M. Laurent, captain of the frigate La Floride. An experiment, made in the laboratory of the École Normal, showed that the spectrum of their light is continuous, without any black rays; it differs, besides, from the spectrum of the solar light by a greater intensity of the yellow colour. The light is produced probably as it is in the case of the Lampyris, by the slow combustion of a substance secreted by the animal. The Cucuyo can, nevertheless, at will, increase or diminish the splendour of this light by means of membranes which it superposes, like screens, in front of the phosphorescent bumps which it has on its thorax.
| Fig. 554. The Cucuyo (Pyrophorus noctilucus). | Fig. 555. Buprestis (Cyria) imperialis. |