Their Sensations

Insects can see, feel, hear, taste and smell, and they may also possess other senses, as a sense of direction. Many insects have two kinds of eyes. On each side of the head the large compound eye is easily recognized (Fig. 1294); each compound eye is composed of many small eyes, from fifty in some ants to many thousands in a butterfly or dragon-fly. Between these compound eyes, from one to four simple eyes are to be found in many adult insects. Caterpillars and other larvae possess only simple eyes. It is thought that each facet of the compound eye sees a part of an object; thus the whole eye would form a mosaic picture on the insect's brain. The simple eyes doubtless see as our eyes do, and seem to be best adapted for use in dark places and for near vision. Insects do not see the form of objects distinctly, but their eyes are doubtless superior to ours in distinguishing the smallest movements of an object. It is now supposed that no insects can distinctly see objects at a greater distance than 6 feet. It must be a sixth sense, a sense of direction, which enables the bee to find its way for a mile or more back to its home. Insects are doubtless able to distinguish the color of objects, and some insects seem to prefer certain colors.

Blue is said to be the favorite color of the honey-bee, and violet that of ants; ants are also apparently sensitive to the ultra-violet rays of light, which man cannot perceive. It is generally supposed that the shape and high colors of flowers attract insects; but recent experiments seem to show that insects are guided to flowers by the sense of smell rather than by sight. The hard outer skin of an insect has no nerves distributed in it, hence it is not sensitive; but it is pierced with holes, in which grow hairs that are in connection with nerves at their base. It is by means of these sensory hairs that insects feel, and are sensitive to touch on most parts of the body. Doubtless insects are not deaf, for we know that many of them make sounds, and it must naturally follow that they have ears to hear, for there is every reason to suppose that they make these sounds as love-songs to attract the sexes, as a means of communication, or possibly to express their emotions. Some think that bees and ants hear sounds too shrill for our ears.

Insects have no true voice, but produce various noises mechanically, either by rapid movements of their wings, which causes the humming of bees and flies, or by friction between roughened surfaces on the body or its appendages, thus producing the rasping sounds or shrill cries of some crickets and grasshoppers. The house-fly hums on F, thus vibrating its wings 335 times in a second, while the wing tone of the honey-bee is A. Usually the males are the musicians of the insect world, but it is the female of the familiar mosquito which does the singing, and the "biting" also. The male mosquito doubtless hears the song of his mate by means of his antennae, as the song causes the antennal hairs to vibrate rapidly. Organs which are structurally earlike have been found in "various parts of the body of insects. The common brown grasshoppers of the fields have a large ear on each side of the first segment of the abdomen; one can easily distinguish with the naked eye the membrane or tympanum stretched over a cavity. Many of the long-horned green grasshoppers, katydids and crickets have two similar ears on the tibia of each front leg. Some think that mosquitos have the faculty of the perception of the direction of sound more highly developed than in any other class of animals.

Insects undoubtedly possess the sense of taste. When morphine or strychnine was mixed with honey, ants perceived the fraud the moment they began to feed. The substitution of alum for sugar was soon detected by wasps. Bees and wasps seem to have a more delicate gustatory sense than flies. Taste organs have been found in many insects, and are usually situated either in the mouth or on the organs immediately surrounding it. Many experiments have shown that the antennae are the principal organs of smell in insects. Blow-flies and cockroaches which have had their antennae removed are not attracted by their favorite food, and male insects find their mates with difficulty when deprived of their antennae. The familiar world which surrounds us may be a totally different place to insects. To them it may be full of music which we cannot hear, of color which we cannot see, of sensations which we cannot perceive. Do insects think or reason? Why not? Their actions are said to be the result of inherited habit or instinct.

But some of them have been seen to do things which require the exercise of instinctive powers so acute and so closely akin to reason that one can hardly escape the conclusion that some insects are endowed with reasoning powers.

Their Sensations 620Their Sensations 621Nymphs of the four lined leaf bug, and adult of the tarnished plant bug.

Fig. 1297. Nymphs of the four-lined leaf-bug, and adult of the tarnished plant-bug.

The smaller one at the left is the nymph recently hatched. The next is the nymph after the first moult. The imago is shown at the right. Hair lines at the right of nymphs, and small figure near imago indicate the natural size.

Larva of a sphinx moth.

Fig. 1298. Larva of a sphinx moth.