When the time of its transformation draws near, the larva, in which stage the insect passes the greater part of its existence, works its way up towards the surface, oftentimes in a very circuitous manner, for local changes make it necessary for it to bore through hard woods and between stones well beaten down. The burrow which it thus produces is cylindrical, about five-eighths of an inch in diameter, and firmly cemented and varnished so as to be water-proof. The upper portion, to the extent of five or six inches, is empty, and serves as a habitation till the period of its exit arrives, while the lower is filled with earthy matter removed by the insect in its progress. In this cell it remains during several days, ascending to the top for the benefit of the sunshine and air when the weather is auspicious, even venturing to peep forth occasionally, but descending on the occurrence of cold or wet weather. But when the favorable moment to leave their subterranean retreats arrives, the Cicada-grubs, or more properly pupæ, for such they are now to be considered, although they still retain something of the grub-like form, issue from the ground in great numbers as evening draws on, crawl up the trunks of trees, the stems of herbaceous plants, or on to whatever is convenient, which they grasp securely with their claws. After resting awhile, their skins, which have become dry and of an amber color, are by repeated exertions rent along the back, and through the slit formed the included Cicada pushes its head and body, and withdraws its wings and legs from their separate cases, and, crawling to a short distance, leaves its empty pupa-case fastened to the tree. At first the wing-covers and wings are small and opaque, but in a few hours they acquire their natural size and shape. It is not, however, for three or four days that the muscles harden sufficiently for them to assume their characteristic flight. The males make their appearance some days in advance of the females, and also disappear sooner. During several successive nights the pupæ continue to issue from the ground, and in some places, as was the case in May of 1868, when these insects appeared in great numbers in the vicinity of Philadelphia, the whole surface of the soil was made by their operations to assume a honey-combed appearance.
DOME-LIKE HOUSE OF CICADA.
Longitudinal Section Showing Pupa in Two Positions.
In localities where the soil is low and swampy, a remarkable chamber is built up by the larva, where the pupa may be found awaiting the time of its change to the winged state. These chambers were first noticed by S. S. Rathvon, at Lancaster, Pa., and are from four to six inches above the ground, and have a diameter of one inch and a quarter. When ready to emerge the insect backs down to an opening which is left in the side of the structure on a level with the surface of the ground, issues forth and undergoes its transformation in the usual manner. This peculiar habit of nest-building, which is so unlike what is customary with the Cicadidæ, or with Hemiptera in general, points to a high degree of intelligence among these insects, showing a remarkable ability to adapt themselves to environing circumstances. Undue moisture would be prejudicial to the pupa, as the larva seemed to know, through the guidance of the same dumb and unerring instinct which teaches it to cement its underground dwelling, but would that same instinct teach it to construct so wonderful a dome-like house as the one described for the preservation of its after-life, and one so eminently fitted by its position, shape, size and entrance to secure the necessary shelter, warmth and air for its protection and development? I apprehend not. Nothing short of a reason, similar to that in man, but differing in degree, would enable it to grasp the situation in which it found itself to be placed when nearing its final change, and plan with the view of carrying out the ultimate aim of its existence.
Fortunately, these insects are appointed to return at periods so distant that vegetation has a chance to recover from the injuries which they inflict. Were they to appear at shorter intervals, our forest- and fruit-trees would be entirely destroyed by them. They are, moreover, subject to many accidents, and have many enemies, which contribute to diminish their numbers. Their eggs are eaten by birds, and the young, when they leave the egg, are preyed upon by ants, who mount the trees for that purpose, or take them upon the ground as they are about to enter upon their protracted larval career. Blackbirds eat them in the spring when turned up by the plough, and hogs, when allowed to run at large in the woods, root them up and devour large numbers, especially just before the arrival of the period of their final transformation, when they are lodged only a few inches below the surface of the soil. Many perish in the egg by the closing up of the bark and wood that constitute the walls of the perforations, thus burying the eggs before they have hatched, and others, no doubt, are killed by their perilous descent from the trees.
As its name implies, this insect generally requires seventeen years to complete its transformations, a fact that was first pointed out many years ago by the botanist Kalm. The late Prof. Riley, who had given this species a great deal of study, was the first to work out the problem of its periodical returns. He found that there are also thirteen-year broods, and that both sometimes occur in the same locality, but that in general terms the thirteen-year brood might be called the southern form, and the seventeen-year the northern form. At the limits of their respective ranges these broods overlap each other. The shorter-lived form he named provisionally Cicada tredecim. It was the existence of this brood that led entomologists to doubt the propriety of Linné’s name, because, in calculating each appearance as occurring in any locality at the end of every seventeen years, they could not make the dates of its periodical returns correct. But it was Prof. Riley that cleared up the matter. It happened in the summer of 1868 that one of the largest seventeen-year broods occurred simultaneously with one of the largest thirteen-year broods. Such an event, so far as these two particular broods are concerned, has not taken place since 1647, nor will it take place again till the year 2089. There are absolutely no specific differences between the two broods other than in the time of maturing. There is, however, a dimorphous form that appears with both these broods. It is smaller, of a much darker color, has an entirely different voice, appears a fortnight sooner, and is never known to pair with the ordinary form. Dr. J. C. Fisher, in 1851, described it as Cicada cassinii, but the specific differences are not sufficiently well defined to entitle it to rank as a species.
HONEY-DEW.
That aphides secrete, or rather excrete, a saccharine fluid, called honey-dew, which constitutes an important part of the food of ants, is a fact well known to naturalists. It must not be supposed, however, that this was its primitive use. But that it is in some way connected with the preservation of the tender creatures by which it is elaborated, there can exist not the slightest doubt.
Concerning its origin and application, and the benefit which it secures to its authors, various opinions have been hazarded, but they have all been too unsatisfactory to merit more than a passing notice. That it was of some advantage to young aphides was surmised by many, but the proofs necessary to sustain such a surmise were unfortunately wanting. It was left to the latter half of the nineteenth century to throw correct light upon the subject.
Whilst engaged some few years ago in the study of the species that affects the blossoms of one of our gourds—the Cucurbita ovifera of botanists—certain phenomena were observed, which promised an easy and speedy solution of the problem.