There are a large number of species, the differentiating features being more or less the form and sculpture of protorax, the size of the head, the length and size of the prosternal spine, the comparative length and size of the hind thighs and shanks, the amount and arrangement of the tegmina mottlings, the comparative length of wings, and the general build of the entire insect, which may be robust or fairly slender.
A general description of the distinctive physical features of migratory locusts might be given as a strong, wild-looking head, a strong collar inside which the neck moves, powerful and peculiarly-formed legs attached to a short, strong, square trunk or thorax, four wings, two antennae or feelers, six legs, and a long segmentary abdomen. The ground colour of the locust is generally brownish, straw, or red, but its colour varies somewhat according to the particular season of the year or some other peculiar circumstance, but nothing certain is known as to what influences the shade of colour. Mere ground colour is immaterial and does not signify a new species.
Besides having a pair of compound eyes which form so noticeable a feature in its head, there are three other simple little eyes, placed like shining dots at three angles of a triangle below the two feelers.
The mouth, which is a fearful apparatus, consists of nine distinct and well-marked organs; an interior or upper lip, consisting of a plate deeply cleft and capable of opening enormously; two true jaws or powerful mandibles; and two pairs of jointed organs called (maxillary) palpi, and two lower jaws. The mandibles and jaws move laterally from right to left.
The thorax or trunk consists really of three rings. To the first is attached the two front legs; to the second, the two middle legs and the first pair of wings, and to the third, the two hind legs and the second pair of posterior wings. Along the posterior margin is a well marked serrated (spinous) arrangement by means of which the locust adheres and grips forcibly. The trunk appears to be full of a fatty sort of substance.
The abdomen consists of a number of horny segments which are joined together by an elastic membrane, a construction which enables the insect to extend its body several centimetres beyond its normal extent. It can also be increased in thickness.
The front and middle feet of this insect are short and weak, but the length, strength, and formation of the hind legs enable it to take extraordinary leaps. A full-grown locust can jump seven or eight feet in height, whilst it is said to be able to leap more than 200 times the length of its body.
The female is normally larger by ¼ or ½ inch in length than the male, and has a rather thicker body.
The average length of the migratory locust is from 2½ to 3 inches and about ⅜ inch in thickness in the abdomen. Locusts generally lay their eggs in the spring, and the manner in which the females, having selected a favourable site, make an excavation in the earth for depositing their eggs is intensely interesting and wonderful.
At the very extremity of the abdomen the female has two pairs of horny valves or hooks, each pair placed back to back with their points directed outwards, and arranged so that all four hooks can be brought with their points close together. By this means a sharp pointed lever is formed which can be turned around, evolved, and forked. With this apparatus she drills a small hole and by means of a series of muscular efforts and the continuing opening and closing of the valves provided with the formation of the abdomen, she actually bores to a depth of 6 to 7 centimetres, or about 3 inches. Here she deposits her eggs—normally about eighty—regularly arranged in a long cylindrical mass and envelopes them in a spumous or sort of glutinous secretion, so that the whole are quite tapped up and level with the surface of the ground. This substance when dried is more or less impassable and affords protection to the eggs from the elements and secures an easy outlet to the surface for the young locust when hatched. The eggs resemble in shape grains of small rice and are about ¼ inch long.