Most physiologists, resting upon the evidence of analogy, agree in attributing five senses to insects: (Dr. Virey, as will be seen further on, ascribes to them seven senses:) though there is a difference of opinion as to the organs by which those senses are conveyed. The antennæ for instance, have been regarded by some as the organs of smell, by others as the organs of touch, and by a third class as the organs of hearing. With the substitution of taste forbearing, the same opinions have been maintained respecting the palpi; nor can the question even now be considered as settled. The prevailing opinion seems to be, that the antennæ are explorers or tactors, but that they are also applied to other uses; the effects produced by their excision indicate that they are organs of the highest importance. Vide [Senses of Bees].
Messrs. Kirby and Spence notice the analogy borne by antennæ to the ears of vertebrate animals, such as their corresponding in number and standing out from the head. No ether organ has been found which can be supposed to represent the ear[L]. And what I have said in another place, of their constituting a sixth sense, has received some countenance from the observations of those naturalists. “I conceive,” says Mr. K., “that the antennæ, by a peculiar structure, may collect notices from the atmosphere, receive pulses or vibrations, and communicate them to the sensorium, which, [communications] though not precisely to be called hearing, may answer the same purpose.” Lehmann calls the function of the antennæ aëroscepsy. A very remarkable instance of the effect produced upon them by sound, is adduced by the authors just quoted, which one of them has thus related. “A little moth was reposing upon my window; I made a quiet, not loud, but distinct noise: the nearest antenna immediately moved towards me. I repeated the noise at least a dozen times, and it was followed every time by the same motion of that organ; till at length the insect, being alarmed, became agitated and violent in its motions. In this instance, it could not be touch; since the antenna was not applied to a surface, but directed towards the quarter from which the sound came, as if to listen.”
[L] Marcel de Serres thinks he has discovered an organ of hearing in most insects, but does not state its situation.
That the antennæ should have been regarded as organs of smell is not surprising when the proceedings of the bees on visiting flowers are considered; their first act is to introduce one of the antennæ, but no further than the tip: this conduct would naturally enough convey the idea of looking or smelling for nectar; yet it does not at all militate against the opinion that the antennæ are transmitters of sound; the sense which they supply may, in these little creatures, be so very fine, as to enable them to hear the bursting of an anther, or the exudation of nectar. The continual motion of the antennæ of insects from side to side, when they walk, conveys the idea that it is by their means that they inform themselves of what is going on in their immediate vicinity. The importance of the antennæ may be inferred from their very complicated structure. Mr. Kirby has observed, that in one species of Apis which he examined, under a powerful magnifier, the ten last joints of the antennæ appeared to be composed of innumerable hexagons, and from this similarity in their structure to the eyes (Vide [Senses of Bees]) he thought that they might serve a somewhat analogous purpose.
What I have said with respect to the Senses of Bees, in another place, will I think make it evident that these insects possess an organ of smell, but with respect to its situation naturalists differ. Baster, Lehmann, and Cuvier, consider the spiracles as the organs of smell, as well as of respiration: this opinion is founded upon the notion that, without the inspiration of air, there can be no smell; and that as insects are smaller than the food they live upon, it would be of no consequence to them where this sense was situated. Kirby and Spence, on the contrary, suppose that it resides in some organ near the mouth: in other parts of the animal creation certainly, that is its situation; and as there seems to be a necessary connection between smell and taste, analogy should lead us to argue in favour of that opinion; but though smell be usually accompanied by respiratory organs, they may not be essentially necessary to it; a bee may receive impressions from external objects, in a manner which we cannot comprehend. In confirmation of this opinion of Kirby and Spence, we have the experiments of Huber. It seems that no odour is so unpleasant to insects as that of oil of turpentine. M. Huber having presented this oil, on the point of a camel’s hair pencil, successively to every part of the abdomen, trunk and head, it excited no uneasiness in the bee: he then tried the eyes and antennæ, but with the same result; yet as soon as he pointed it a little above the insertion of the proboscis, near the cavity of the mouth, the bee receded, became agitated, clapped its wings, and would have taken flight, had not the pencil been withdrawn. This experiment was repeated with the turpentine and other articles of penetrating odour, and with the same effect; but when the mouths of several bees were stopped with paste, no such consequences ensued, on the contrary they traversed the impregnated pencils without being at all annoyed by them; even honey did not attract them. All these circumstances tend to prove that the site of smelling is in or near the mouth.—This subject will be resumed in [Chap. XXXII.]
Organs of Respiration.
The respiration of bees is performed through several little orifices, called stigmata, spiracles, or breathing pores, situated in the sides of their bodies, behind their wings. Reaumur was of opinion that inspiration was performed through the spiracles, and expiration through the mouth; but Bonnet proved satisfactorily that neither inspiration nor expiration takes place through the mouth. The spiracles are connected with a system of air-vessels called tracheæ, ramifying through every part of the frame, and serving the purpose of lungs. From the absence of lungs, Aristotle and the ancients in general thought that insects did not breathe. Pliny may perhaps be excepted, for he has observed that dipping bees in honey or oil deprives them of life;—this immersion stops up the mouths of the spiracles. Modern physiologists have however incontestibly proved that they do breathe. “Life and flame,” says Cuvier, “have this in common, that neither the one nor the other can subsist without air; all living beings, from man to the most minute vegetable, perish when they are utterly deprived of that fluid.” Huber detected the existence of the stigmata or breathing pores, by immersing different portions of a bee in water, and finally by total immersion, upon which he observed that bubbles of air attached themselves for some time to the orifices of the stigmata, which alternately appeared and receded, till their increased bulk enabled them to overcome the resistance of inspiration and rise to the surface. These respiratory organs escaped the observation of Swammerdam.
Air is equally necessary to insects in the egg state: Spallanzani found that their eggs could not be hatched in small close vessels, though all other circumstances were favourable to a development. The eggs of the hive-bee, whilst in the ovaries, have a net-work of air-vessels spread over their surfaces;—these were discovered by Swammerdam: from analogy, we may reasonably conclude, that such a provision obtains generally.
The closeness of a hive, and its having no direct current of air through it, may favour a belief that bees can exist in any atmosphere, however vitiated, and may seem also to confirm the opinion of the ancients, that they have no particular system of respiratory organs. But M. Huber and Son have proved that they breathe like other animals, that they are speedily deprived of life, if the process of respiration be arrested; so delicate indeed is their organization, that they detect the smallest deterioration in the atmosphere of their hives, and immediately adopt measures to restore to this element the degree of purity essential to respiration: from some eudiometrical experiments, it has been ascertained that the air of a well stocked hive is as pure as that by which it is surrounded. Still neither wax nor pollen favours the generation of oxygen gas, nor have bees the faculty of generating it; for when very closely shut up, they perish in a few hours. The writers just referred to, discovered that the bees, by uniting the two wings of each side, by means of the small marginal hooks with which they are provided, so as to make them present the largest possible surface to the air, were capable of striking it with considerable force, and that this force was increased by the wings forming a slight concavity. The wings arranged in this manner, are put into a violent vibratory motion by the bees appointed to the office of ventilators, and produce what we call a draught of air. Ventilation is thus systematically accomplished. A certain portion of ventilating bees is stationed in files at the entrance of the hive, with their heads turned inwards; another and a larger party, in files also, stands a considerable way in the interior, with their heads towards the entrance: thus both these parties cooperate, in producing a current of air in the same direction, and are so arranged as not to interrupt the passage of their fellow-citizens, moving in and out. As this hard duty has no intermission during the day, nor in hot weather during the night, and must necessarily occasion fatigue, one set of ventilators is considerately relieved in about twenty-five minutes, by another set of fresh bees. Under particular circumstances the number of ventilating bees is considerably increased. “When the air,” says Huber, “was not renewed in the manner desirable, we have seen all vibrating their wings at once, though this never occurs in the natural state, when the vibrations of a few are sufficient for ventilation.” Although this fanning motion of the wings is so rapid as to render them almost indistinguishable, yet they may be observed to describe an arc of 90°. The sagacious bees remind me of a method which is sometimes adopted of renewing the air of a room, called pumping; some person moves the door backward and forward so rapidly as to cause a thorough agitation of the confined air, and the introduction of a fresh unvitiated atmosphere. “When they are engaged in ventilation, the bees by means of their feet and claws, fix themselves as firmly as possible, to the place they stand upon. The first pair of legs is stretched out before; the second extended to the right and left: whilst the third, placed very near each other, are perpendicular to the abdomen, so as to give that part considerable elevation.” That ventilation is carried on for the purpose of renewing the air of the hives, and not for lowering its temperature, is evident from its being continued to a certain extent, even during the depth of winter.
The vibratory motion of the bee’s wings has been regarded by some as the principal cause of the humming noise heard in every prosperous hive during the busy season. This humming has likewise been attributed to the rushing of the air through their spiracles: so thought M. Chabrier, and, I believe, Mr. J. Hunter. Mr. H. assures us that bees can produce a sound independently of their wings; for if these be smeared over with honey so as to stick together, the bee still makes a noise, which is shrill and peevish. He found the same effect from holding the bee by the legs, with a pair of pincers, while the wings were perfectly still, and also by immersing the insect in water, though not till it was very much teased.