The Glow-Worm and Other Beetles. Fabre Jean-Henri
and in perfect order? Some action must take place here independent of the Sitares.
To satisfy those two indispensable conditions, the arrival of the larva upon the egg without crossing the honey and the introduction of a single larva among all those waiting in the fleece of the Bee, there can be only one explanation, which is to suppose that, at the moment when the Anthophora's egg is half out of the oviduct, one of the Sitares which have hastened from the thorax to the tip of the abdomen, one more highly favoured by its position, instantly settles upon the egg, a bridge too narrow for two, and with it reaches the surface of the honey. The impossibility of otherwise fulfilling the two conditions which I have stated gives to the explanation which I am offering a degree of certainty almost equivalent to that which would be furnished by direct observation, which is here, unfortunately, impracticable. This presupposes, it is true, in the microscopic little creature destined to live in a place where so many dangers threaten it from the first, an astonishingly rational inspiration, which adapts the means to the end with amazing logic. But is not this the invariable conclusion to which the study of instinct always leads us?
When dropping her egg upon the honey, therefore, the Anthophora at the same time deposits in her cell the mortal enemy of her race; she carefully plasters the lid which closes the entrance to the cell; and all is done. A second cell is built beside it, probably to suffer the same fatal doom; and so on until the more or less numerous parasites sheltered by her down are all accommodated. Let us leave the unhappy mother to continue her fruitless task and turn our attention to the young larva which has so adroitly secured itself board and lodging.
In opening cells whose lid is still moist, we end by discovering one in which the egg, recently laid, supports a young Sitaris. This egg is intact and in irreproachable condition. But now the work of devastation begins: the larva, a tiny black speck which we see running over the white surface of the egg, at last stops and balances itself firmly on its six legs; then, seizing the delicate skin of the egg with the sharp hooks of its mandibles, it tugs at it violently until it breaks, spilling its contents, which the larva eagerly drinks up. Thus the first stroke of the mandibles which the parasite delivers in the usurped cell is aimed at the destruction of the Bee's egg. A highly logical precaution! The Sitaris-larva, as we shall see, has to feed upon the honey in the cell; the Anthophora-larva which would proceed from that egg would require the same food; but the portion is too small for two; so, quick, a bite at the egg and the difficulty will be removed. The story of these facts calls for no comment. This destruction of the cumbersome egg is all the more inevitable inasmuch as special tastes compel the young Sitaris-grub to make its first meals of it. Indeed we see the tiny creature begin by greedily drinking the juices which the torn wrapper of the egg allows to escape; and for several days it may be observed, at one time motionless on this envelope, in which it rummages at intervals with its head, at others running over it from end to end to rip it open still wider and to cause a little of the juices, which become daily less abundant, to trickle from it; but we never catch it imbibing the honey which surrounds it on every side.
For that matter, it is easy to convince ourselves that the egg combines with the function of a life-buoy that of the first ration. I have laid on the surface of the honey in a cell a tiny strip of paper, of the same dimensions as the egg; and on this raft I have placed a Sitaris-larva. Despite every care, my attempts, many times repeated, always failed. The larva, placed in a paper boat in the centre of the mass of honey, behaves as in the earlier experiments. Not finding what suits it, it tries to escape and perishes in the sticky toils as soon as it leaves the strip of paper, which it soon does.
On the other hand, we can easily rear Sitaris-grubs by taking Anthophora-cells not invaded by the parasites, cells in which the egg is not yet hatched. All that we have to do is to pick up one of these grubs with the moistened tip of a needle and to lay it delicately on the egg. There is then no longer the least attempt to escape. After exploring the egg to find its way about, the larva rips it open and for several days does not stir from the spot. Henceforth its development takes place unhindered, provided that the cell be protected from too rapid evaporation, which would dry up the honey and render it unfit for the grub's food. The Anthophora's egg therefore is absolutely necessary to the Sitaris-larva, not merely as a boat, but also as its first nourishment. This is the whole secret, for lack of knowing which I had hitherto failed in my attempts to rear the larvæ hatched in my glass jars.
At the end of a week, the egg, drained by the parasite, is nothing but a dry skin. The first meal is finished. The Sitaris-larva, whose dimensions have almost doubled, now splits open along the back; and through a slit which comprises the head and the three thoracic segments a white corpusculum, the second form of this singular organism, escapes to fall on the surface of the honey, while the abandoned slough remains clinging to the raft which has hitherto safeguarded and fed the larva. Presently both sloughs, those of the Sitaris and the egg, will disappear, submerged under the waves of honey which the new larva is about to raise. Here ends the history of the first form adopted by the Sitaris.
In summing up the above, we see that the strange little creature awaits, without food, for seven months, the appearance of the Anthophoræ and at last fastens on to the hairs on the corselet of the males, who are the first to emerge and who inevitably pass within its reach in going through their corridors. From the fleece of the male the larva moves, three or four weeks later, to that of the female, at the moment of coupling; and then from the female to the egg leaving the oviduct. It is by this concatenation of complex manoeuvres that the larva in the end finds itself perched upon an egg in the middle of a closed cell filled with honey. These perilous gymnastics on the hair of a Bee in movement all the day, this passing from one sex to the other, this arrival in the middle of the cell by way of the egg, a dangerous bridge thrown across the sticky abyss, all this necessitates the balancing-appliances with which it is provided and which I have described above. Lastly, the destruction of the egg calls, in its turn, for a sharp pair of scissors; and such is the object of the keen, curved mandibles. Thus the primary form of the Sitares has as its function to get itself carried by the Anthophora into the cell and to rip up her egg. This done, the organism becomes transformed to such a degree that repeated observations are required to make us believe the evidence of our eyes.
CHAPTER IV
THE PRIMARY LARVA OF THE OIL-BEETLES
I interrupt the history of the Sitares to speak of the Meloes, those uncouth Beetles, with their clumsy belly and their limp wing-cases yawning over their back like the tails of a fat man's coat that is far too tight for its wearer. The insect is ugly in colouring, which is black, with an occasional blue gleam, and uglier still in shape and gait; and its disgusting method of defence increases the repugnance with which it inspires us. If it judges itself to be in danger, the Meloe resorts to spontaneous bleeding. From its joints a yellowish, oily fluid oozes, which stains your fingers and makes them stink. This is the creature's blood. The English, because of its trick of discharging oily blood when on the defensive, call this insect the Oil-beetle. It would not be a particularly interesting Beetle save for its metamorphoses and the peregrinations of its larva, which are similar in every respect to those of the larva of the Sitares. In their first form, the Oil-beetles are parasites of the Anthophoræ; their tiny grub, when it leaves the egg, has itself carried into the cell by the Bee whose victuals are to form its food.
Observed in the down of various Bees, the queer little creature for a long time baffled the sagacity of the naturalists, who, mistaking its true origin, made it a species of a special family of wingless insects. It was the Bee-louse (Pediculus apis) of Linnæus;17 the Triungulin of the Andrenæ (Triungulinus andrenetarum) of Léon Dufour. They saw in it a parasite, a sort of Louse, living in the fleece of the honey-gatherers. It was reserved for the distinguished English naturalist Newport to show that this supposed Louse was the first state of the Oil-beetles. Some observations of my own will fill a few lacunæ in the English scientist's monograph. I will therefore sketch the evolution of the Oil-beetles, using Newport's work where my own observations are defective. In this way the Sitares and the Meloes, alike in habits and transformations, will be compared; and the comparison will throw a certain light upon the strange metamorphoses of these insects.
The same Mason-bee (Anthophora pilipes) upon whom the Sitares live also feeds a few scarce Meloes (M. cicatricosus) in its cells. A
Carolus Linnæus (Karl von Linné, 1707-1778), the celebrated Swedish botanist and naturalist, founder of the Linnæan system of classification. —