True Tales of the Insects
level with the skin, surrounded by a simple horny ring; or it may be somewhat depressed, a portion of the segment projecting a little over it; and sometimes it is very sunken in the abdomen, the arched and horny sides projecting over it so much that nothing is seen externally save a sort of slit wMth a cavity or pit beneath it. In the last condition the organ exists in the genera Mecostethus and Stenobothrus, which are among our native grasshoppers. It is usually conceded that this ear consists of a tympanum supphed internally with an auditory nerve and a ganglion, besides muscles, and tracheal apparatus; it is undoubtedly a sense-organ of an extremely delicate nature. It is found in both sexes, as in most of the species of Acridiidse. The forms in which it is absent are generally at the same time wingless, and destitute of organs for producing special sound.
Yet to decide as to the exact function of these earlike acoustic organs is a matter of extreme difficulty. We know, from the fact that the insects are easily disturbed, that the sense of hearing must be delicate, and the Acridiidae with ears are believed to be sensitive to sounds by means other than these organs. This suggests that the purpose of the latter is the perception of special sound. What can this be? Is it the fiddling or stridulating sound which we have seen they produce? Any insect having elaborate sound-producing organs must be supposed to have ears to hear the sound
produced by others of its own species. No doubt the effective sound-producing instruments are, apparently, confined to the male, while the ears exist in both sexes. But this need give rise to no difficulty, for it is generally thought that the female has pleasure in the music of the male. The real obstacle at present to the acceptance of these organs as being special structures for the perception of the music of the species, lies in the fact of the existence of the acoustic organs in species that do not, ^
This Tyndall has ilkistrated in his work on Sound. " Crossing the Wengern Alp with a friend," he says, " the grass on each side of the path swarmed with insects, which, to me, rent the air with their shrill chirruping. My friend heard nothing of this, the insect world lying beyond his limit of audition." In other words, as Scudder remarks, sounds become inaudible to many persons when they are derived from vibrations more rapid than 25,000 per second, and when the number becomes 38,000, the limit of human perceptibility is reached. This difference in sensitiveness to vibration of human ears, renders it, of course, more probable that ears so unlike our own as are those of insects may be capable of detecting sounds of a shrillness of which the best human ear can hear nothing. We may perhaps then conclude that these Acridiidse with ears, and to all appearances dumb, do really produce sounds, though beyond our range of perception, and do so by some method unknown to us. If this be the case, it is probable that the function of these ears is the hearing of particular sounds.
Oviposition; and Philosophy of the Egg-mass.
The details of the process of oviposition of the Acridiid?e are of much interest. The insect has no
elongate exserted ovipositor for placing the eggs in suitable positions, but possesses instead four short horny appendages, or gonapophyses, which, from their peculiar structure, are admirably adapted for digging. By means of these, when about to lay, she excavates a hole in the ground; there is no perforation of the soil, the hinder part of the body is merely forced into it. With the valves closed, she inserts the tips into ground, and by a series of muscular efforts, and the alternate opening and shutting of the valves, in this way it is easy to press the earth aside, and in a few minutes nearly the whole of the abdomen is buried. Along with the eggs a quantity of viscous fluid is discharged, that binds all the eggs in a mass, and when the last egg is laid, the viscous matter continues to be shed, filling up, as with a stopper or cork, the orifice of the cavity. The Rocky Mountain Locust stops the neck of its hole with a compact and cellulose mass of the material, which, though light and easily penetrated, is more or less impervious to water. The operation complete, but little trace is left of it; most often the frothy secretion rises above the burrow of the Algerian migratory locust. When fresh the mass is soft and moist, but soon the fluid deposited dries, acquiring a firm consistency, and forms an excellent protection to the eggs, corresponding to the more definite capsules of cursorial Orthoptera.
The insect in ovipositing prefers a hard and compact
soil to that which is loose, and may be observed at its excavations even on beaten paths. The time required to accomplish this strenuous task will vary according to the season and temperature. In the event of a frost at night, and the insects not rousing from their chilled inactivity till 9 a.m., the Rocky Mountain Locusts have been observed to be scarcely able to make the hole and complete the pod during the four or five warmer hours of the day; but with higher temperature not more than about half that time would be needed.
Their period of ovipositing extends over about sixty-two days, the average number of egg-masses formed being probably three or four, and the total number of eggs deposited about a hundred. The French naturalists recently record a similar fact in Algeria, and have ascertained that ScJiistoccrca pcrcgrina, one of the migratory locusts, may deposit eggs at more than one of the spots on which it may alight during its migration. A careful study of the egg-mass, or egg-pod, of Calopienus sprchis and other locusts, will reveal a quadrilinear arrangement of the esfSfs, not onlv so as to economize space, but so as to best facilitate the escape of the young. Clearly if, from whatever cause, the upper eggs should hatch later than the lower, or should fail to is hatch—as not unfrequently the exit of the young would case—the be impeded were there no provision against such a possibility. Without touching upon the channel obtained.
along which the exit is easily made, it may be mentioned that the posterior or narrow end of the ^gg of Caloptenus sp7'etiis points downwards in the egg-mass, so that the exit of the young from the anterior end is thus rendered easier. The quadrilinear arrangement of the eggs is by no means constant, even in the same genus. But even in the pods of those species of Caloptenus which have the eggs irregularly arranged, the head ends commonly point either outward or inward, so that the newly-hatched creature may push out at the sides or through a central space.
Egg-Encuiies.
Notwithstandintj the mother's care, fearful are the odds against the development of her progeny. Ere yet the locust is born, from the moment it starts life as an &gg, enemies stand in wait to cut short its career. The smaller of these animals, belonging principally to its own class, carry on this good work most effectually. We altogether undervalue the usefulness of these tiny foes in helping to keep the locust in check, simply because they are often scarcely perceptible, and their work too often goes on hid and unobserved.
Beetles of the family Cantharid^e hover in the localities where the eggs are laid and insert their eggs in the H
egg-masses of AcridiidEe, which may thus be entu'ely destroyed. In North America the so-called Locust Mite proves a bitter enemy to the locust. In the mature form it lives in the ground, feeding upon all sorts of soft animal and decomposing vegetable matter. When the grasshopper fills the holes with its eggs, the mites flourish thereon, creeping into the holes and eating the contents voraciously. A most common and widespread egg-enemy is the Anthomyia egg-parasite. The Muscinae, owing to the rapidity of their successive generations, destroy large quantities of the eggs of the migratory locust. The flies follow the locusts, and when they settle to lay eggs, they also alight, ready to bore their way to the eggs, with deadly results. It is said the Dipterous genus Idia is incapable of boring into light and sand)- soils, and for this reason Acridmm peregrinuiiL chooses them. Two-winged flies of the family Bombyliidae are also parasitic in these eggs. Kilnckel d'Herculais has studied the Bombylid larvcc found in the ova ot the devastating locust Stauronotus maroccanics. The larva issues from the ecrof in August, reaches the limit of its growth in October, and passing the winter within the egg-case, is hatched the following summer.
To this work of egg-destruction by insect enemies and parasites, must be added the good offices of various birds, and of some mammals. Hogs are quite fond of locust eggs, and soon learn to search them out.
] ^oiing from the Egg. Of the Escape of the
It is usual for all the young in a given mass to burst from the ^g'g very nearly at one and the same time, and in that event the lowermost individuals await the escape of those in front, which first push out through the neck of their earthy dwelling. One after the other, through one small hole, they all escape into the light of day. The actual method of hatching of Staiironotus viaroccanus, as described by Kunckel d'Herculais, is most interesting. According to him, an ampulla plays the principal part in the process. To escape from the capsule, the young Stauronotus puts into action an ampulla formed by the cutaneous membrane between the head and the prothorax. This ampulla is the more effective in being dilated by fluid from the body cavity, and is maintained in the swollen condition by the insect accumulating air in the crop. Each capsule is closed with a well-htting cover, and to detach it, six or seven of the young ones inside unite their efforts to push it off by help of their ampullar. Nature has supplied these young ones with tools: sharp mandibles, powerful legs, furnished with spines and claws; but these seem not yet at their service, for a reason to be presently discovered.
We have by no means exhausted the important and
loo TRUE TALES OF THE INSECTS.
multitarious functions of this apparatus, the ampulla. It subsequently serves as a sort of reservoir, by aid of which the insect can diminish the bulk of other parts of the body, and thus after emergence from the capsule, penetrate the narrowest cracks in the soil, so as to reach the surface. As soon as it is there the young Stauronotus moults; the ampulla enables it to burst and to get rid of the skin in which it is enveloped. Freed of this pellicle, the young, no longer swaddled, can now make use of their limbs for walking and leaping, and have free use of their antennae and buccal parts. At every moult the cervical ampulla reappears, and plays the leading role at these crises assigned to it.
But in the process of hatching of the Rocky Mountain Locust, Riley speaks of the feet as playing the principal part. By a continued series of undulating movements, and by the action of the sharp tip of the hind tibial spines, as also of the tarsal claws of all the legs, he finds the egg-shell is ruptured, and the nascent larva soon succeeds in working free therefrom and making its way to the light. Once on the surface of the ground, it rests for a moment, almost motionless. It is soft and limp, its members are still directed backward, and it is yet fettered in the very delicate film or pellicle, which must be cast before the newly-emerged creature can move with freedom. The skin begins to split, and in from one to five minutes from the time the insect arrives above ground,