The antennæ ([Fig, 6, a, a]) are the horn-like jointed organs situated between or below and in front of the large compound eyes of all insects. They are sometimes short, as in the house-fly, and sometimes very long, as in the grasshoppers. They are either straight, curved or elbowed ([Fig, 6]). In form, too, they are very various, as thread-like, tapering, toothed, knobbed, fringed, feathered, etc. It is known that a nerve passes into the antennæ, but their exact function is little understood. That they serve as most delicate touch organs no apiarist can doubt. That they serve as organs of smell or hearing is not proved. That insects are conscious of sounds I think no observing person can doubt. It is proved by the call of the katy-did, the cicada and the cricket. What apiarist, too, has not noticed the effect of various sounds made by the bees upon their comrades of the hive. How contagious the sharp note of anger, the low hum of fear, and the pleasant tone of a new swarm as they commence to enter their new home. Now, whether insects take note of these vibrations, as we recognize pitch, or whether they just distinguish the tremor, I think no one knows. There is some reason to believe that their delicate touch-organs may enable them to discriminate between vibrations, even more acutely, than can we by use of our ears. A slight jar will quickly awaken a colony of hybrids, while a loud noise will pass unnoticed. If insects can appreciate with great delicacy the different vibratory conditions of the air by an excessive development of the sense of touch, then undoubtedly the antennæ may be great aids. Dr. Clemens thought that insects could only detect atmospheric vibrations. So, too, thought Linnæus and Bonnet. Siebold thinks, as the antennæ receive but one nerve, and are plainly touch-organs, they cannot be organs of hearing. Kirby has noticed that some moths turn their antennæ towards the direction from which noise proceeds, and thus argues that antennæ are organs of hearing. Grote, for a similar reason, thinks that the densely feathered antennæ of the males of various night moths, serve both for smell and hearing. Prof. A. M. Mayer and Mr. C. Johnson (see American Naturalist, vol. 8, p. 574) have by various ingenious experiments, proved conclusively, that the delicate, beautifully feathered antennæ of the male mosquito are organs of hearing.
That insects have a very refined sense of smell is beyond question. How quickly the carrion-fly finds the carcass, the scavenger the filth, and the bee the precious nectar.
I have reared female moths in my study, and have been greatly surprised on the day of their leaving their cocoons, to find my room swarming with males. These bridegrooms entered an open window in the second-story of a brick building. How delicate must have been the sense by which they were led to make the visit, and thus made to grace my cabinet. Bees, too, have been known to dash against a shutter behind which were flowers, thus showing the superiority of their perception of odors, as also their poor vision. But odors are carried by the air, and must reach the insect through this medium. Is it not probable, that the various breathing mouths of insects are also so many noses, and that their delicate lining membranes abounding with, nerve filaments, are the great odor sentinels? This view was maintained by both Lehman and Cuvier, and explains this delicate perception of scents, as the breathing mouths are large and numerous, and most so in insects like bees and moths, which are most sensitive to odors. How quickly the bees notice the scent of a strange bee or queen, or the peculiar odor of the venom. I have known a bee to sting a glove, and in a trice the glove would be as a pin-cushion, with stings in lieu of pins. Sometimes the bees will dart for many feet, guided by this odor. Yet the odor is very pungent, as I have frequently smelt the poison before I felt the sting. I have tried the experiments of Huber and Lubbock, and know that such insects as bees and ants will take no note of food after the loss of their antennæ. But we must remember that this is a capital operation. With loss of antennæ, insects lose control of their motions, and in many ways show great disturbance. Is it not probable then that removing the antennæ destroys the desire for food, as does amputation with ourselves? Kirby believes with Huber, that there is a scent organ. Huber's experiments on which he based this opinion are, as usual, very interesting. He presented a coarse hair dipped in oil of turpentine—a substance very repugnant to bees—to various parts of a bee engrossed in sipping honey. The bee made no objection, even though it touched the ligula, until it approached the mouth above the mentum, when she became much disturbed. He also filled a bee's mouth with paste, which soon hardened, after which the bee paid no heed to honey placed near it. This was not so conclusive, as the bee may have been so disturbed as to lose its appetite. I have experimented a good deal, and am inclined to the following opinion: The antennæ are very delicate touch-organs or feelers, and are so important in their function and connection that removal produces a severe shock, but further we know but little about their function, if they have other, and from the very nature of the problem we will find it very difficult of solution.
The eyes are of two kinds, the compound, which are always present in mature insects, and the ocelli or simple eyes, which may or may not be present. When present there are usually three, which if we join by lines, we will describe a triangle, in the vertices of whose angles are the ocelli. Rarely there are but two ocelli, and very rarely but one.
The simple eyes ([Fig, 4, f f f]) are circular, and possess a cornea, lens and retina, which receives the nerve of sight.
From the experiments of Réaumur and Swammerdam, which consisted in covering the eyes with varnish, they concluded that vision with these simple eyes is very indistinct, though by them the insect can distinguish light. Some have thought that these simple eyes were for vision at slight distances. Larvæ, like spiders and myriapods, have only simple eyes.
The compound eyes ([Fig, 2, e]) are simply a cluster of simple eyes, are situated one on either side of the head, and vary much in form and size. Between or below these are inserted the antennæ. Sometimes these last are inserted in a notch of the eyes, and in a few cases actually divide each eye into two eyes.
The eyes may meet above as in drones ([Fig, 4]), most two-wing flies and dragon-flies, or they may be considerably separated, as in the worker-bees ([Fig, 5]). The separate facets or simple eyes, of each compound eye, are hexagonal, or six-sided, and in the microscope look not unlike a section of honey-comb. The number of these is prodigious—Leeuwenhoek actually counted 12,000 in the eye of a dragon-fly—while some butterflies have, over 17,000. The compound eyes are motionless, but from their size and sub-spherical shape, they give quite a range of vision. It is not likely that they are capable of adjustment to accord with different distances, and it has been supposed, from the direct darting flight of bees to their hives, and the awkward work they make in finding a hive when moved only for a short distance, that their eyes are best suited to long vision.
Sir John Lubbock has proved, by some interesting experiments with strips of colored paper, that bees can distinguish colors. Honey was placed on a blue strip, beside several others of various colors. In the absence of the bees he changed the position of this strip, and upon their return the bees went to the blue strip rather than to the old position. Our practical apiarists have long been aware of this fact, and have conformed their practice to the knowledge, in giving a variety of colors to their hives. Apiarists have frequently noted that bees have a rare faculty of marking positions, but, for slight distances, their sense of color will correct mistakes which would occur if position alone was guide.