These precautions will be foiled. The enemy will succeed in penetrating the impregnable fortress; each foe has his special tactics, contrived with appalling skill. See, an egg is inserted by means of a probe beside the torpid larva; or else, in the absence of such an implement, an infinitesimal grub, an atom, comes creeping and crawling, slips in and reaches the sleeper, who will never wake again, already a succulent morsel for her ferocious visitor. The interloper makes the victim's cell and cocoon his own cell and his own cocoon; and next year, instead of the mistress of the house, there will come from below ground the bandit who usurped the dwelling and consumed the occupant.
Look at this one, striped black, white and red, with the figure of a clumsy, hairy Ant. She explores the slope on foot, inspects every nook and corner, sounds the soil with her antennae. She is a Mutilla, the scourge of the cradled grubs. The female has no wings, but, being a Wasp, she carries a sharp poniard. To novice eyes she would easily pass for a sort of robust Ant, distinguished from the common ruck by her garb of staring motley. The male, wide-winged and more gracefully shaped, hovers incessantly a few inches above the sandy expanse. For hours at a time, on the same spot, after the manner of the Scolia-wasp he spies the coming of the females out of the ground. If our watch be patient and persevering, we shall see the mother, after trotting about for a bit, stop somewhere and begin to scratch and dig, finally laying bare a subterranean gallery, of which there was nothing to betray the entrance; but she can discern what is invisible to us. She penetrates into the abode, remains there for a while and at last reappears to replace the rubbish and close the door as it was at the start. The abominable deed is done: the Mutilla's egg has been laid in another's cocoon, beside the slumbering larva on which the newborn grub will feed.
Here are others, all aglitter with metallic gleams: gold, emerald, blue and purple. They are the humming-birds of the insect-world, the Chrysis-wasps, or Golden Wasps, another set of exterminators of the larvae overcome with lethargy in their cocoons. In them, the atrocious assassin of cradled children lies hidden under the splendour of the garb. One of them, half emerald and half pale-pink, Parnopes carnea by name, boldly enters the burrow of Bembex rostrata at the very moment when the mother is at home, bringing a fresh piece to her larva, whom she feeds from day to day. To the elegant criminal, unskilled in navvy's work, this is the one moment to find the door open. If the mother were away, the house would be shut up; and the Golden Wasp, that sneak-thief in royal robes, could not get in. She enters, therefore, dwarf as she is, the house of the giantess whose ruin she is meditating; she makes her way right to the back, all heedless of the Bembex, her sting and her powerful jaws. What cares she that the home is not deserted? Either unmindful of the danger or paralysed with terror, the Bembex mother lets her have her way.
The unconcern of the invaded is equalled only by the boldness of the invader. Have I not seen the Anthophora-bee, at the door to her dwelling, stand a little to one side and make room for the Melecta to enter the honey-stocked cells and substitute her family for the unhappy parent's? One would think that they were two friends meeting on the threshold, one going in, the other out!
It is written in the book of fate: everything shall happen without impediment in the burrow of the Bembex; and next year, if we open the cells of that mighty huntress of Gad-flies, we shall find some which contain a russet-silk cocoon, the shape of a thimble with its orifice closed with a flat lid. In this silky tabernacle, which is protected by the hard outer shell, is a Parnopes carnea. As for the grub of the Bembex, that grub which wove the silk and next encrusted the outer casing with sand, it has disappeared entirely, all but the tattered remnants of its skin. Disappeared how? The Golden Wasp's grub has eaten it.
Another of these splendid malefactors is decked in lapis-lazuli on the thorax and in Florentine bronze and gold on the abdomen, with a terminal scarf of azure. The nomenclators have christened her Stilbum calens, FAB. When Eumenes Amedei (A species of Mason-wasp.—Translator's Note.) has built on the rock her agglomeration of dome-shaped cells, with a casing of little pebbles set in the plaster, when the store of Caterpillars is consumed and the secluded ones have hung their apartments with silk, we see the Stilbum take her stand on the inviolable citadel. No doubt some imperceptible cranny, some defect in the cement, allows her to insert her ovipositor, which shoots out like a probe. At any rate, about the end of the following May, the Eumenes' chamber contains a cocoon which again is shaped like a thimble. From this cocoon comes a Stilbum calens. There is nothing left of the Eumenes' grub: the Golden Wasp has gorged herself upon it.
Flies play no small part in this brigandage. Nor are they the least to be dreaded, weaklings though they be, sometimes so feeble that the collector dare not take them in his fingers for fear of crushing them. There are some clad in velvet so extraordinarily delicate that the least touch rubs it off. They are fluffs of down almost as frail, in their soft elegance, as the crystalline edifice of a snowflake before it touches ground. They are called Bombylii.
With this fragility of structure is combined an incomparable power of flight. See this one, hovering motionless two feet above the ground. Her wings vibrate so rapidly that they appear to be in repose. The insect looks as though it were hung at one point in space by some invisible thread. You make a movement; and the Bombylius has disappeared. You cast your eyes in search of her around you, far away, judging the distance by the vigour of her flight. There is nothing here, nothing there. Then where is she? Close by you. Look at the point whence she started: the Bombylius is there again, hovering motionless. From this aerial observatory, as quickly recovered as quitted, she inspects the ground, watching for the favourable moment to establish her egg at the cost of another creature's destruction. What does she covet for her offspring: the honey-cupboard, the stores of game, the larvae in their transformation-sleep? I do not know yet, What I do know is that her slender legs and her dainty velvet dress do not allow her to make underground searches. When she has found the propitious place, suddenly she will swoop down, lay her egg on the surface in that lightning touch with the tip of her abdomen and straightway fly up again. What I suspect, for reasons set forth presently, is that the grub that comes out of the Bombylius' egg must, of its own motion, at its own risk and peril, reach the victuals which the mother knows to be close at hand. She has no strength to do more; and it is for the new-born grub to make its way into the refectory.
I am better acquainted with the manoeuvres of certain Tachinae, the tiniest of pale-grey Flies, who, cowering on the sand in the sun, in the neighbourhood of a burrow, patiently await the hour at which to strike the fell blow. Let a Bembex-wasp return from the chase, with her Gad-fly; a Philanthus, with her Bee; a Cerceris, with her Weevil; a Tachytes, with her Locust: straightway the parasites are there, coming and going, turning and twisting with the Wasp, always at her rear, without allowing themselves to be put off by any cautious feints. At the moment when the huntress goes indoors, with her captured game between her legs, they fling themselves on her prey, which is on the point of disappearing underground, and nimbly lay their eggs upon it. The thing is done in the twinkling of an eye: before the threshold is crossed, the carcase holds the germs of a new set of guests, who will feed on victuals not amassed for them and starve the children of the house to death.
This other, resting on the burning sand, is also a member of the Fly tribe; she is an Anthrax. (Cf. "The Life of the Fly": chapter 2.—Translator's Note.) She has wide wings, spread horizontally, half smoked and half transparent. She wears a dress of velvet, like the Bombylius, her near neighbour in the official registers; but, though the soft down is similar in fineness, it is very different in colour. Anthrax is Greek for coal. It is a happy denomination, reminding us of the Fly's mourning livery, a coal-black livery with silver tears. The same deep mourning garbs those parasitic Bees, and these are the only instances known to me of that violent opposition of dead black and white.