When the young Insect is in the egg, ready for emergence, the meso- and meta-thorax are not remarkably elongate, so that the femora are not very far apart, but by the time the creature has fairly emerged from the prison of its embryonic life the thoracic segments have attained their usual proportions; much expansion of the body takes place as the Insect leaves the egg, so that it appears a marvel how it could have been contained therein; this expansion affects the parts of the body unequally.
The records as to the post-embryonic development of Phasmidae are very scanty, but indicate great differences in the length of time occupied by it. Bacillus patellifer is said to moult several times, Diapheromera femorata only twice. This latter species becomes full grown in six weeks, while, according to Murray,[[191]] Phyllium scythe required fifteen or sixteen months for growth, and did not moult until ten months after hatching; the number of ecdyses in the case of the Phyllium was three. At each change of skin an immediate increase in size, similar to that we have noticed as occurring on leaving the egg, takes place; each limb on being freed becoming about a fourth longer and larger than the corresponding part of the envelope from which it has just been withdrawn. After the second moult of Phyllium the tegmina and wings made their appearance, but remained of very small size until after the third moult, when they suddenly shot out to their full size; they came out of little cases about a quarter of an inch long, and in the course of a few minutes attained their full size of about two and a half inches of length. In the apterous species the difference between the young and adults in external characters is very slight.
Fig. 151.—Ceroys saevissima. Brazil. (After Westwood.)
Phasmidae are very sensitive to cold; both in North America and Australia their lives are terminated by the occurrence of frost. They are all vegetable feeders, the cannibalism that has been attributed to them by several writers being probably imaginary. They are, however, excessively voracious, so that a pair will destroy a great quantity of foliage; they are consequently in some parts of the world classed amongst injurious Insects. In Fiji and the Friendly Islands, Lopaphus cocophagus eats the cocoa-nut foliage and causes a scarcity of food, so that it becomes a matter of necessity to destroy these Insects. One writer has gone so far as to attribute the occurrence of cannibal habits amongst the inhabitants of some of these islands to the want of food caused by the ravages of this Insect. Some, if not all, of the Phasmidae have the habit of ejecting a stinking fluid, that is said to be very acrid, and occasionally, when it strikes the eye, to cause blindness; this liquid comes from glands placed in the thorax. Some Phasmidae are much relished as food by birds; Diapheromera femorata is sucked by several bugs as well as eaten by birds, and another species is recorded to have harboured Ichneumon-flies in its body without suffering any apparent inconvenience from their presence or from their emergence. Notwithstanding the great amount of food they consume and their want of activity, they produce comparatively few eggs. From twelve to twenty or thirty is frequently mentioned as about the number, but in the case of Diapheromera femorata Riley speaks of upwards of one hundred. These eggs are not deposited in any careful way, but are discharged at random, simply dropping from the female; the noise caused by the dropping of the eggs of Diapheromera femorata from the trees on which the Insects are feeding to the ground is said to resemble the pattering of raindrops. The eggs of this species often remain till the second year before they hatch. The eggs in the Phasmidae generally are of a most remarkable nature, and nearly every one who mentions them speaks of their extreme resemblance to seeds. Göldi[[192]] has suggested that this is for the purpose of deceiving Ichneumons; it is, however, on record that the eggs are actually destroyed by Ichneumons. It is worthy of notice that the eggs are shed like seeds, being dropped loosely and, as we have said, remaining on the ground or elsewhere, sometimes for nearly two years, without other protection than that they derive from their coverings. Each egg is really a capsule containing an egg, reminding us thus of the capsule of the Blattidae, which contains, however, always a number of eggs. Not only do the eggs have a history like that of seeds, and resemble them in appearance, but their capsule in minute structure, as we shall subsequently show, greatly resembles vegetable tissue. The egg-capsule in Phasmidae is provided with a lid, which is pushed off when the Insect emerges (Fig. 157). This capsule induced Murray to suppose that the egg contained within is really a pupa, and he argued therefrom that in the Orthoptera the larval stages are passed in the egg, and that the Insect after its emergence should be looked on as an active pupa that takes food.
Fig. 152.—Eggs of Phasmidae: A, Lonchodes duivenbodi; B, Platycrania edulis; C, Haplopus grayi; D, Phyllium siccifolium. (After Kaup.)
The individuals of this group of Insects possess the power of reproducing a lost limb; and Scudder, who has made some experiments as to this,[[193]] states that if a leg be cut off beyond the trochantero-femoral articulation, the parts remaining outside of this joint are dropped before the next moult, and are afterwards renewed either as a straight short stump in which the articulations are already observable, or as a miniature leg, the femur of which is straight and the tibia and tarsus curved into a nearly complete circle; in the former case, the leg assumes at the next moult the appearance that it has in the second case; this latter form is always changed at the succeeding moult into a leg resembling the normal limb in every respect excepting size, and the absence of the fourth tarsal joint (Fig. 153). If the leg be removed nearer to the body than the trochantero-femoral articulation the limb is not replaced.
The sexes are frequently extremely different; the female is usually very much larger than the male. This latter sex often possesses wings when they are quite wanting in the other sex; the resemblance to portions of plants is often very much greater in the female than it is in the male.
