In the autumn three more generations of aphides are produced, two of which generally make their appearance in the month of August, and the third before the middle of September. The two first differ in no respect from those which are found in summer; but the third differs greatly from all the rest. Though all the aphides which have hitherto appeared were females, in this tenth generation several male insects are found, but not by any means so numerous as the females.
The females have at first the same appearance with those of the former generations, but in a few days their colour changes from a green to a yellow, which is gradually converted into an orange before they come to their full growth; they differ also in another respect from those which occur in summer, for all these yellow females are without wings. The male insects are, however, still more remarkable, their outward appearance readily distinguishing them from this and all other generations. When first produced, they are not of a green colour like the rest, but of a reddish brown, and have afterwards a dark line along the back; they come to their full growth in about three weeks, and then cast off their last covering, the whole insect being after this of a bright yellow colour, the wings only excepted; but after this change to a deeper yellow, and in a very few hours to a dark brown, if we except the body, which is something lighter coloured, and has a reddish cast. The males no sooner come to maturity than they copulate with the females, who in a day or two after their intercourse with the males lay their eggs, generally near the buds. Where there are a number crowded together, they of course interfere with each other, in which case they will frequently deposit their eggs on other parts of the branches. It is highly probable that the aphides derive considerable advantages by living in society; the reiterated punctures of a great number of them may attract a larger quantity of nutritious juices to that part of the tree or plant where they have taken up their abode.
The aphides are very injurious to trees and vegetables of almost every kind; the species is so numerous, and all endued with so much fertility, that if they were not destroyed by a numerous host of enemies, the leaves, the branches, and the stem of every plant would be covered with them. On almost every leaf inhabited by aphides, a small worm is to be found, that feeds not upon the leaves, but upon these insects, devouring them with incredible rapacity: Reaumur supplied a single worm with above one-hundred aphides, every one of which it devoured in less than three hours. Indeed myriads of insects seem to be produced for no other purpose than to destroy them.
OF THE APIS OR BEE.
The bee belongs to the hymenoptera order, the mouth is furnished with two jaws, and a proboscis protected by a double sheath, see Fig. 3. [Plate XIII.] They have four wings; when these are at rest, the two foremost cover those behind. There is a sting in the tail of the working and female bee. Of the bee kind fifty-five species are enumerated by Linnæus. Our present observations are confined to the common or domestic bee.
In the natural history of insects new objects of surprize are continually rising before the observer: however singular the preceding account of the production of the aphides may appear, that of bees is not less so. This little republic has at all times gained universal esteem and admiration; and, though they have attracted the attention of the most ingenious and laborious inquirers into nature, yet the mode of propagating their species seems to have baffled the ingenuity of ages, and rendered all attempts to discover it abortive; even the labours and scrupulous attention of Swammerdam were unsuccessful. He spent one month entirely in examining, describing, and representing their intestines; and many months on other parts; employing whole days in making observations, and whole nights in registering them, till at last he brought his treatise of bees to the wished for perfection; a work which, from the commencement of natural history to our own times, has not its equal. Reaumur, however, thought he had in some measure removed the veil, and explained their manner of generating: he supposes the queen bee to be the only female in the hive, and the mother of the next generation; that the drones are the males, by which she is fecundated, and that the working bees, or those that collect wax on the flowers, that knead it, and form from it the combs and cells, which they afterwards fill with honey, are of neither sex. The queen bee is known by its size, being generally much larger than the working bee or the drone.
M. Schirach, a German naturalist, affirms that all the common bees are females in disguise, in which the organs that distinguish the sex, and particularly the ovaria, are obliterated, or at least from their extreme minuteness have escaped the observer’s eye; that every one of these bees, in the earlier period of its existence, is capable of becoming a queen bee, if the whole community should think it proper to nurse it in a particular manner, and raise it to that rank: in short, that the queen bee lays only two kinds of eggs, those that are to produce the drones, and those from which the working bees are to proceed. Schirach made his experiments not only in the early spring months, but even as late as November. He cut off from an old hive a piece of the brood-comb, taking care that it contained worms which had been hatched about three days. He fixed this in an empty hive, together with a piece of honey-comb, for food to his bees, and then introduced a number of common bees into the hive. As soon as these found themselves deprived of their queen and their liberty, a dreadful uproar took place, which lasted for the space of twenty-four hours. On the cessation of this tumult, they betook themselves to work, first proceeding to the construction of a royal cell, and then taking the proper methods for feeding and hatching the brood inclosed with them; sometimes even on the second day the foundation of one or more royal cells were to be perceived; the view of which furnished certain indications that they had elected one of the inclosed worms to the sovereignty. The bees may now be left at liberty. The final result of these experiments is, that the colony of working bees being thus shut up with a morsel of brood-comb, not only hatch, but at the end of eighteen or twenty days produce from thence one or two queens, to all appearance proceeding from worms of the common sort, converted by them into a queen merely because they wanted one.[82] From experiments of the same kind, varied and often repeated, Schirach concludes that all the common working bees were originally of the female sex; but that if they are not fed, lodged, and brought up in a particular manner while they are in the larva state, their organs are not developed; and that it is to this circumstance attending the bringing up the queen, that the extension of the female organs is effected, and the difference in her form and size produced.
[82] Schirach Histoire Naturelle des Abeilles.
Mr. Debraw has carried the subject further, by discovering the impregnation of the eggs by the males, and the difference of the size among the drones or males; though indeed this last circumstance was not unknown to Mess. Maraldi and Reaumur. Mr. Debraw watched the glass hives with indefatigable attention, from the moment the bees, among which he took care there should be a large number of drones, were put into them, to the time of the queen’s laying her eggs, which generally happens on the fourth or fifth day; he observed, that on the first or second day, always before the third from the time the eggs are placed in the cells, a great number of bees, fastening themselves to one another, hung down in the form of a curtain, from the top to the bottom of the hive; they had done the same at the time the queen deposited her eggs, an operation which seems contrived on purpose to conceal what is transacting; however, through some parts of this veil he was enabled to see some of the bees inserting the posterior part of their bodies each into a cell, and sinking into it, but continuing there only a little while. When they had retired, it was easy to discover a whitish liquor left in the angle of the basis of each cell, which contained an egg. In a day or two this liquor was absorbed into the embryo, which on the fourth day assumes its worm or larva state, to which the working bees bring a little honey for nourishment, during the first eight or ten days after its birth. When the bees find the worm has attained its full growth, they leave off bringing it food, they know it has no more need of it; they have still, however, another service to pay it, in which they never fail; it is that of shutting it up in its cell, where the larva is inclosed for eight or ten days: here a further change takes place; the larva, which was heretofore idle, now begins to work, and lines its cell with fine silk, while the working bee incloses it exteriorly with a wax covering. The concealed larva then voids its excrement, quits its skin, and assumes the pupa; at the end of some days the young bee acquires sufficient strength to quit the slender covering of the pupa, tears the wax covering of its cell, and proceeds a perfect insect.
To prove further that the eggs are fecundated by the males, and that their presence is necessary at the time of breeding, Mr. Debraw made the following experiments. They consist in leaving in a hive the queen, with only the common or working bees, without any drones, to see whether the eggs she laid would be prolific. To this end he took a swarm, and shook all the bees into a tub of water, leaving them there till they were quite senseless; by which means he could distinguish the drones without any danger of being stung: he then restored the queen and working bees to their former state, by spreading them on a brown paper in the sun; after this he replaced them in a glass hive, where they soon began to work as usual. The queen laid eggs, which, to his great surprize, were impregnated, for he imagined he had separated all the drones or males, and therefore omitted watching them; at the end of twenty days he found several of his eggs had, in the usual course of changes, produced bees, while some had withered away, and others were covered with honey. Hence he inferred, that some of the males had escaped his notice, and impregnated part of the eggs. To convince himself of this, he took away all the brood-comb that was in the hive, in order to oblige the bees to provide a fresh quantity, being determined to watch narrowly their motions after new eggs should be laid in the cells. On the second day after the eggs were deposited, he perceived the same operation that was mentioned before, namely, that of the bees hanging down in the form of a curtain, while others thrust the posterior part of their bodies into the cells. He then introduced his hand into the hive, broke off a piece of the comb, in which there were two of these insects; he found in neither of them any sting, a circumstance peculiar to the drones; upon dissection, with the assistance of a microscope, he discovered the four cylindrical bodies which contain the glutinous liquor of a whitish colour, as observed by Maraldi in the large drones. He was therefore now under the necessity of repeating his experiments, in destroying the males, and even those that might be suspected to be such. He once more immersed the same bees in water, and when they appeared in a senseless state, he gently pressed every one, in order to distinguish those armed with stings from those which had none, and which of course he supposed to be males: of these last he found fifty-seven, and replaced the swarm in a glass hive, where they immediately applied again to the work of making cells, and on the fourth or fifth day, very early in the morning, he had the pleasure to see the queen bee deposit her eggs in those cells: he continued watching most part of the ensuing days, but could discover nothing of what he had seen before.