Bee Abdomen


Respiratory Organs—Circulation of Nutritive Fluid—Digestion and Nutrition—Secretion of Wax—Reproductive Organs—Detailed description of Sting—Effects of Poison—Queen’s Sting.

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The abdomen constitutes the largest and hindmost segment of the body, and is important as containing several structures which have most essential functions in the economy of the insect. Among these are the chief parts of the respiratory apparatus, the digestive, the wax-making, the reproductive, and stinging organs.

First, it must be noted that the bee has nothing strictly analogous to our lungs, heart, liver, and other structures making up a true circulating-system. At the same time there is a real oxygenation of the fluids of the body, with a consequent evolution of heat, water, and carbonic acid gas.

The breathing apparatus has not its aperture for inspiration and expiration situated in the head, as is the case in the higher animals; but air is admitted and expelled through apertures along both sides of the body. In the thorax are two pairs of such openings, and there is a pair on each ring of the abdomen.

These air-holes are called spiracles, or stigmata, and lead into two minute chambers, one behind the other, the outer being provided with a number of short hairs, to prevent the entry of foreign particles likely to obstruct the important passages.

Fig. 32.—Abdomen of Bee, Showing Respiratory Organs.
a, Air-sac.      b b b, Spiracles.

From these vestibules the air is conducted by tubes, or tracheæ, into sacs or bladders communicating with each other. The largest pair of these cavities is found in the abdomen, and from these two main trunks lead, one into the thorax, and the other to the termination of the abdomen. From the latter there branch out subsidiary tubes, leading into the minuter chambers, called sacculi, or little sacs.

Those going upwards do not subdivide till they reach the head, in which are found two air-chambers of considerable size. Reasons for this distribution of the secreting vessels may be found, on the one hand, in the need of the oxygenation of the tissues, especially those connected with the nutrition of the ganglia of highest functions; and, on the other, in the requirements of buoyancy in the segments relatively the heaviest, and destitute of organs of support in the atmosphere, such as the wings furnish.

A confirmation of the second of these purposes is derived from the remarkable fact, that in the queen bee, who does not fly more than once or twice in her life, the great air-sacs of the abdomen are almost obliterated, their space being needed for the large ovaries.

Fig. 33.—Air-sacs of Worker.

The structure of the tracheæ is very remarkable. Under a powerful microscope they are seen to consist of a double membrane, between the two coats of which are coils of an elastic thread, which act like the spiral wire frequently used for keeping open and strengthening india-rubber tubing. By means of this structure the air-pipes are maintained in a condition for the free passage of the atmosphere, and if closed by pressure, the elastic fibre reopens them directly the pressure is removed.

Fig. 34.—a, Air-sacs, b, Ovaries, of the Queen.

With regard to the circulation of the nutritive fluid in the system, considerable obscurity prevails. What is known is, that along the back of the insect runs a vessel called, from its position, the dorsal vessel, attached to the outer covering of the body by bands of ligamentous tissue.

The portion of this tube contained in the abdomen is enlarged at intervals into chambers communicating with each other by valves, which allow the fluid to go forward to the head, but not back towards the other extremity. Passing by a simple elastic tube through the thorax, the blood, if we may so call it, is propelled to the anterior segment of the body.

Its subsequent course is not very clear; for, while some anatomists speak of a small vessel leading back to the hinder part of the body, others consider that the sanguineous, or nutritive, liquid finds its way from the cephalic parts to other vital organs, and after bathing them, returns to the dorsal vessel by a second set of valves permitting its ingress only.

Fig. 35.—a, Tracheæ; b, Elastic Spiral of Tracheæ.

Turning next to the nutritive organs, we have already spoken at sufficient length of the mouth and its appendages, and have mentioned that the nectar of flowers is conveyed first to an enlargement of the gullet, analogous to the crop of birds. From this, some is regurgitated by the workers into the cells, for storage, while another portion passes on to the true stomach.[4] 

A certain amount of nitrogenous food, chiefly pollen, also finds its way to this cavity, and there undergoes a second mastication by the so-called gastric teeth. These consist of silica, and are therefore very hard.

[4]Pastor Schönfeld has recently made some most interesting researches into the anatomy and communication of the two stomachs. A translation of his articles may be found in The British Bee Journal for July, 1883.

After undergoing considerable digestion in the stomach, the chyle, as we may now consider it, passes into a short intestine, where it receives fluid from the so-called “biliary ducts.” Further on is an expansion, called the colon, after traversing which the portions of food not absorbed into the system, together with the waste products brought to the intestines, are expelled from the body.

It is probable that the nutritive parts of the aliment find their way through the walls of the intestine, and mingling with the sanguineous liquid returned from the cephalic extremity, pass with it into the dorsal vessel.

Closely connected with the digestive apparatus is that which is concerned in the making of wax. By pressing the abdomen of the bee, so as to cause its extension, there can be seen, on the under side of the four medial ventral segments, two trapeziform whitish pockets, one on either side of the carinæ, or elevated central part.

These are of a membranous texture, and are covered with a reticulation of hexagonal meshes, reminding one of the inner coat of the second stomach of the sheep, and other ruminating animals. There is no direct communication between the stomach and these pockets; but Hunter suggested that the secreting surface is in the membrane just alluded to.

Fig. 36.—Under Side of Abdomen, Showing Wax Scales.

Fig. 38.—Scales.
Fig. 37.—Bee, Showing the Wax Scales.

We cannot follow the process by which the change from honey to wax is effected, any more than we can account for the elaboration of bile, saliva, and the pancreatic liquid, from our blood by the different organs connected with their production. All we can say is, that the membrane of the wax-receptacles is endowed with the peculiar power of transforming the nectar of flowers into an oil.

The actual chemical change may be stated in general terms thus: Honey and sugar contain, roughly speaking, equal chemical equivalents of oxygen, carbon, and hydrogen. In wax, the quantities of the first of these elements is diminished to about an eighth part, while the carbon and hydrogen are more than quadrupled. In other words, the saccharine material suffers very great de-oxidation in passing into the condition of wax.

The wax-oil, when it has filled the pocket in which it is secreted, passes out of the body of the insect in laminæ or scales, which take the shape of the bags in which they have been produced. In contact with the air, the wax absorbs a small quantity of oxygen, and loses an equal amount of carbon.

When about to be used by the bee, it is picked off the under segments of the body by the hind-legs, passed on to the fore-feet, and by them is conveyed to the mouth, where, by being mixed with saliva and well kneaded, it is rendered pliant, ductile, and more tenacious.

The reproductive organs of the queen consist, first, of two large bags, one on each side of the abdomen, and called ovaries, in which the eggs are generated. When mature, these eggs pass by a tube from each ovary to a common duct, on one side of which is found a small yellow vesicle, called the spermatheca

On examination under the microscope, this is found to be filled with a viscous fluid, in which, with a lens of high power, may be seen moving thousands of spermatozoa derived from the drone.

Fig. 39.—Ovaries and Spermatheca of Queen.

By voluntary effort on the part of the queen, each egg, as it passes this vesicle, may be touched with a most minute drop of the fluid just mentioned. Then this very marvellous fact results. An egg thus fertilised develops into a queen or a worker, according to the conditions under which it is hatched; while those eggs which are not brought in their passage into contact with the fluid, and receive no spermatozoa, become drones.

Herein lies the explanation of fertile workers giving birth to drones only, and of queens, hatched after the drones of a season are dead, also laying eggs which will develop only into male bees. We are absolutely unable to account for these most extraordinary circumstances, which open up interesting fields for future investigation. Not the least wonderful point is the exercise of will, on the part of the queen, in the production of the particular kind of egg which, without making mistakes, she lays in the cells specially provided for the three classes of her offspring.

The last of the abdominal organs we have now to describe, is one which is not essential to the life of the individual, but has been conferred by the Creator as a means of offence and defence, viz., the sting. Those who have frequently felt its effects have no need to be told how formidable a weapon it is; but few probably are fully acquainted with the structures which give it such potent force.

If a bee be irritated, and made to thrust out its sting, we observe a dark brown and sharply-pointed dart. This, when magnified, is seen to be the sheath, in which the true sting lies and is moved. The sheath is divided down the centre, and between the two parts the real piercers work, though the sheath itself is thrust into the wound. It consists of two horny scales, smooth and closely adherent to the true darts.

These last are stiff filaments, barbed along their outer edge. They are not quite equal in length, so that the teeth of the one do not lie exactly opposite those of the other. They work side by side, and, possibly with alternate motion, pierce deeper and deeper into the punctured material. The teeth give a firm hold to the imbedded weapon, and prevent its easy withdrawal.

In fact, when plunged into human flesh, or into thick leather gloves, these barbs hold so tightly that the insect is unable to free itself, and if forcibly detached, or if by a vigorous effort it escapes, the sting is left behind, and frequently attached to it are portions of the viscera. The bee thus loses its life, and the injury it inflicts is the more severe.

Fig. 40.—Sting of a Bee, greatly magnified.

The mere puncture of the weapon, however, would be a quite unimportant matter, were it not that, connected with the groove in which the dart works, is a short tube leading from a bag containing a liquid of the most acrid and poisonous nature. By powerful muscles, attached to the upper part of the sting, the barbs are thrust out; the sheath follows them into the pierced substance, and then, by the pressure of other muscles, a drop of the poison-liquid runs down into the wound, and immediately sets up a violent pain and inflammation of the surrounding parts.

So powerful is the action of the irritant, that numerous cases are on record of death ensuing through its influence. We are, however, bound to say that, by many authorities, such fatal consequences are considered to result from syncope produced by fright, rather than from the direct effect of the poison on the nervous system. Still, there is no doubt of the very formidable nature of the liquid, as may be generally seen in the amount of swelling and discomfort caused by the exceedingly minute portion injected by the sting of a bee.

Fig. 41.—Barbs of a Bee’s Sting, very highly magnified.

The most remarkable function of the sting-apparatus has, in modern times, been discovered to be the insertion of a minute drop of the poison in each honey-cell when filled. This acts as an anti-septic, and prevents fermentation in the sweet liquid.

The poison is secreted by tiny glands, from which it is conveyed, by tubes or ducts, into the reservoir, where it is stored ready for use. Chemically, the liquid is said to have an acid reaction. Hence the application of ammonia, and other alkaline solutions, will most effectually counteract its effects.

The sting of the queen differs from that of the worker, in having its barbs curved, instead of straight. This modification makes it a much less formidable implement. Moreover, it is very seldom employed. It is, indeed, almost impossible to make a queen sting the hand, even by great provocation. Almost the only circumstances in which her majesty employs the weapon are, first, for mortal combat with a rival, and second, for murdering, if permitted by the workers, the princesses before they emerge from the cells in which they have developed.

The drone is without a sting, and, indeed, seems never to show fight at all. Its jaws might furnish no despicable weapons, but the insect seems to lack spirit to use them, even in self-defence, and when attacked by the mandibles only of the workers, manifests no inclination to employ its own against its tormentors.

Struggles to escape, and haste to flee, seem to betray its absence of courage; though, possibly, an instinctive knowledge that its assailants have in reserve a more deadly piece of armour than strong jaws may make “discretion the better part of valour.”

With regard to the sting of the bee, Paley aptly remarks that it “affords a beautiful example of the union of chemistry and mechanism: of chemistry in respect to the venom, which, in so small a quantity, can produce such powerful effects; of mechanism, as the sting is not a simple but a compound instrument. 

The machinery would have been useless, had it not been for the chemical process, by which, in the insect’s body, honey is converted into poison; and, on the other hand, the poison would have been ineffectual without an instrument to wound, and a syringe to inject the fluid.”

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