Elementary Zoology, Second Edition

by Vernon L. Kellogg

Examine the wings. In what ways do the front wings differ from the hind wings? The front wings are known as the wing covers or tegmina. Note how the hind wings fold up like a fan, and are covered and protected by the wing covers. Draw the wings.

The abdomen is composed of a number of segments most of which resemble each other. The first segment (immediately behind the metathorax) has its dorsal and ventral parts widely separated by the cavities for the insertion of the hindmost legs. The ventral part of this segment is dovetailed into the ventral part of the metathorax and appears to be part of it. In the dorsal part of this segment there is on each side a spot where the cuticle is only a thin membrane. At these places are the auditory organs or ears of the locust. The thin membranes are the tympana. Only the various kinds of locusts and those insects closely related to them have ears of this kind. Most other insects are believed to have the sense of hearing situated in the antennæ.

The abdominal segments from second to eighth are ring-like in form and are without appendages. There is on the side of each of these segments near its front margin a tiny opening or pore called a spiracle. These spiracles are the breathing pores of the locust, which does not take in air through its mouth or any other opening in the head. There is a spiracle near each ear in the first abdominal segment, and one on each side of the mesothorax near the insertion of the middle legs.

The terminal segments of the abdomen are provided with certain processes which are different in male and female. The female has at the tip of its abdomen two pairs of strong, curved pointed pieces which compose the ovipositor, or egg-laying organ. The opening of the oviduct lies between the pieces. The male has a swollen rounded abdominal tip, with three short inconspicuous pieces on the dorsal surface.

Make a drawing of the lateral aspect of the abdomen of a female locust; also, of a male.

For a more detailed account of the external anatomy of a locust see Comstock and Kellogg's "Elements of Insect Anatomy," chap. II.

The external structure of the grasshopper should be carefully compared with that of the crayfish; pay special attention to the mouth-parts and legs.

The teacher should point out the homologies and modifications.

Life-history and habits.—The eggs of the locust are laid in the autumn in the ground in bare dry places, as roadsides, closely-grazed pastures, etc. The female thrusts her strong ovipositor into the soil, and by opening and shutting it, thus boring, pushes in the abdomen for about two thirds its length. The eggs, about one hundred, are then deposited in a capsule or pod. The young locusts hatch in the following spring. When just hatched they resemble the parent locust in general appearance and structure except that they lack wings, and are of course very small. The young locusts are gregarious, congregating in warm and sunny places. They feed on green plants and travel about by walking and hopping. At night they try to find shelter under rubbish in the fields. They feed voraciously and grow rapidly, reaching maturity in about two months. During this post-embryonic development and growth they molt (shed the chitinous exoskeleton) five times. After the first molt indications of the wings appear in the shape of small backward and downward prolongations of the posterior margins of the dorsum of the mesothorax and metathorax. With each succeeding molt these wing-pads, or developing wings, are larger and more wing-like, until after the last molting they appear fully developed. With each molting, too, there is a marked increase in size of the locust, the average length of the body just before the first moult being 4.3 mm., before the second 6.8 mm., before the third 9 mm., before the fourth 14 mm., before the fifth 17 mm., and after the fifth (the full-grown stage) about 26 mm.

The molting is an interesting process, and can be readily observed. The young locust ready for its last molt crawls up some post, weed, grass stalk, or other object, and clutches this object securely with the hind feet. The head is generally downward. The locust remains motionless in this position for several hours, when the skin suddenly splits along the back from the middle of the head to the base of the abdomen. By steady swelling and contracting and slight wriggling, lasting for half an hour to three-fourths of an hour, the old skin is completely shed, and the wings spread out. In an hour the wings are dry and the new chitinized exoskeleton firm enough for flying, or crawling about, and in another hour the locust begins to eat.