I obtain Anthrax sinuata ("The Mason-bees": chapters 8, 10 and 11.—Translator's Note.) from various bees' nests. When she issues from the cocoons of the Three-horned Osmia, especially the female cocoons, she attains the greatest development that I know of. When she issues from the cocoons of the Blue Osmia (O. cyanea, KIRB.), she is sometimes hardly one-third the length which the other Osmia gives her. And we still have the two sexes—that goes without saying—and still identically the same species.
Two Anthidia, working in resin, A. septemdentatum, LATR., and A. bellicosum, LEP. (For these Resin-bees, cf. "Bramble-bees and Others": chapter 10.—Translator's Note.), establish their domicile in old Snail-shells. The second harbours the Burnt Zonitis (Z. proeusta (Cf. "The Glow-worm and Other Beetles": chapter 6.—Translator's Note.)). Amply nourished this Meloe then acquires her normal size, the size in which she usually figures in the collections. A like prosperity awaits her when she usurps the provisions of Megachile sericans. (For this Bee, the Silky Leaf-cutter, cf. "Bramble-bees and Others": chapter 8.—Translator's Note.) But the imprudent creature sometimes allows itself to be carried away to the meagre table of the smallest of our Anthidia (A. scapulare, LATR. (A Cotton-bee, cf. idem: chapter 9.—Translator's Note.)), who makes her nests in dry bramble-stems. The scanty fare makes a wretched dwarf of the offspring belonging to either sex, without depriving them of any of their racial features. We still see the Burnt Zonitis, with the distinctive sign of the species: the singed patch at the tip of the wing-cases.
And the other Meloidae—Cantharides, Cerocomae, Mylabres (For these Blister-beetles or Oil-beetles, cf. "The Glow-worm and Other Beetles": chapter 6.—Translator's Note.)—to what inequalities of size are they not subject, irrespective of sex! There are some—and they are numerous—whose dimensions fall to a half, a third, a quarter of the regular dimensions. Among these dwarfs, these misbegotten ones, these victims of atrophy, there are females as well as males; and their smallness by no means cools their amorous ardour. These needy creatures, I repeat, have a hard life of it. Whence do they come, these diminutive Beetles, if not from dining-rooms insufficiently supplied for their needs? Their parasitical habits expose them to harsh vicissitudes. No matter: in dearth as well as in abundance the two sexes appear and the specific features remain unchanged.
It is unnecessary to linger longer over this subject. The demonstration is completed. The parasites tell us that changes in the quantity and quality of food do not lead to any transformation of species. Fed upon the larva of the Three-horned Osmia or of the Blue Osmia, Anthrax sinuata, whether of handsome proportions or a dwarf, is still Anthrax sinuata; fed upon the allowance of the Anthidium of the empty Snail-shells, the Anthidium of the brambles, the Megachile or doubtless many others, the Burnt Zonitis is still the Burnt Zonitis. Yet variation of diet ought to be a very potential factor in the problem of progress towards another form. Is not the world of living creatures ruled by the stomach? And the value of this factor is unity, changing nothing in the product.
The same parasites tell us—and this is the chief object of my digression—that excess or deficiency of nutriment does not determine the sex. So we are once more confronted with the strange proposition, which is now more positive than ever, that the insect which amasses provisions in proportion to the needs of the egg about to be laid knows beforehand what the sex of this egg will be. Perhaps the reality is even more paradoxical still. I shall return to the subject after discussing the Osmiae, who are very weighty witnesses in this grave affair. (Cf. "Bramble-bees and Others": chapters 3 to 5. The student is recommended to read these three chapters in conjunction with the present chapter, to which they form a sequel, with that on the Osmiae (chapter 2 of the above volume) intervening.—Translator's Note.)
CHAPTER 10. THE BEE-EATING PHILANTHUS.
To meet among the Wasps, those eager lovers of flowers, a species that goes hunting more or less on its own account is certainly a notable event. That the larder of the grub should be provided with prey is natural enough; but that the provider, whose diet is honey, should herself make use of the captives is anything but easy to understand. We are quite astonished to see a nectar-drinker become a blood-drinker. But our astonishment ceases if we consider things more closely. The double method of feeding is more apparent than real: the crop which fills itself with sugary liquid does not gorge itself with game. The Odynerus, when digging into the body of her prey, does not touch the flesh, a fare absolutely scorned as contrary to her tastes; she satisfies herself with lapping up the defensive drop which the grub (The Larva of Chrysomela populi, the Poplar Leaf-beetle.—Translator's Note.) distils at the end of its intestine. This fluid no doubt represents to her some highly-flavoured beverage with which she seasons from time to time the staple diet fetched from the drinking-bar of the flowers, some appetizing condiment or perhaps—who knows?—some substitute for honey. Though the qualities of the delicacy escape me, I at least perceive that the Odynerus does not covet anything else. Once its jar is emptied, the larva is flung aside as worthless offal, a certain sign of a non-carnivorous appetite. Under these conditions, the persecutor of the Chrysomela ceases to surprise us by indulging in the crying abuse of a double diet.
We even begin to wonder whether other species may not be inclined to derive a direct advantage from the hunting imposed upon them for the maintenance of the family. The Odynerus' method of work, the splitting open of the anal still-room, is too far removed from the obvious procedure to have many imitators; it is a secondary detail and impracticable with a different kind of game. But there is sure to be a certain variety in the direct means of utilizing the capture. Why, for instance, when the victim paralysed by the sting contains a delicious broth in some part of its stomach, should the huntress scruple to violate her dying prey and force it to disgorge without injuring the quality of the provisions? There must be those who rob the dead, attracted not by the flesh but by the exquisite contents of the crop.
In point of fact, there are; and they are even numerous. We may mention in the first rank the Wasp that hunts Hive-bees, the Bee-eating Philanthus (P. apivorus, LATR.). I long suspected her of perpetrating these acts of brigandage on her own behalf, having often surprised her gluttonously licking the Bee's honey-smeared mouth; I had an inkling that she did not always hunt solely for the benefit of her larvae. The suspicion deserved to be confirmed by experiment. Also, I was engaged in another investigation, which might easily be conducted simultaneously with the one suggested: I wanted to study, with all the leisure of work done at home, the operating-methods employed by the different Hunting Wasps. I therefore made use, for the Philanthus, of the process of experimenting under glass which I roughly outlined when speaking of the Odynerus. It was even the Bee-huntress who gave me my first data in this direction. She responded to my wishes with such zeal that I believed myself to possess an unequalled means of observing again and again, even to excess, what is so difficult to achieve on the actual spot. Alas, the first-fruits of my acquaintance with the Philanthus promised me more than the future held in store for me! But we will not anticipate; and we will place the huntress and her game together under the bell-glass. I recommend this experiment to whoever would wish to see with what perfection in the art of attack and defence a Hunting Wasp wields the stiletto. There is no uncertainty here as to the result, there is no long wait: the moment when she catches sight of the prey in an attitude favourable to her designs, the bandit rushes forward and kills. I will describe how things happen.