Here is a partial explanation of the double system of the Hymenoptera with their carnivorous larvæ—the system of dead or paralysed insects followed by honey. But here the point of interrogation, already encountered elsewhere, erects itself once again. Why is the larva of the Osmia, which thrives upon albumen, actually fed upon honey during its early life? Why is a vegetable diet the rule in the hives of bees from the very commencement, when the other members of the same series live upon animal food?
If I were a "transformist" how I should delight in this question! Yes, I should say: yes, by the fact of its germ every animal is originally carnivorous. The insect in particular makes a beginning with albuminoid materials. Many larvæ adhere to the alimentation present in the egg, as do many adult insects also. But the struggle to fill the belly, which is actually the struggle for life, demands something better than the precarious chances of the chase. Man, at first an eager hunter of game, collected flocks and became a shepherd in order to profit by his possessions in time of dearth. Further progress inspired him to till the earth and sow; a method which assured him of a certain living. Evolution from the defective to the mediocre, and from the mediocre to the abundant, has led to the resources of agriculture.
The lower animals have preceded us on the way of progress. The ancestors of the Philanthus, in the remote ages of the lacustrian tertiary formations, lived by capturing prey in both phases—both as larvæ and as adults; they hunted for their own benefit as well as for the family. They did not confine themselves to emptying the stomach of the bee, as do their descendants to-day; they devoured the victim entire. From beginning to end they remained carnivorous. Later there were fortunate innovators, whose race supplanted the more conservative element, who discovered an inexhaustible source of nourishment, to be obtained without painful search or dangerous conflict: the saccharine exudation of the flowers. The wasteful system of living upon prey, by no means favourable to large populations, has been preserved for the feeble larvæ; but the vigorous adult has abandoned it for an easier and more prosperous existence. Thus the Philanthus of our own days was gradually developed; thus was formed the double system of nourishment practised by the various predatory insects which we know.
The bee has done still better; from the moment of leaving the egg it dispenses completely with chance-won aliments. It has invented honey, the food of its larvæ. Renouncing the chase for ever, and becoming exclusively agricultural, this insect has acquired a degree of moral and physical prosperity that the predatory species are far from sharing. Hence the flourishing colonies of the Anthophoræ, the Osmiæ, the Euceræ, the Halicti, and other makers of honey, while the hunters of prey work in isolation; hence the societies in which the bee displays its admirable talents, the supreme expression of instinct.
This is what I should say if I were a "transformist." All this is a chain of highly logical deductions, and it hangs together with a certain air of reality, such as we like to look for in a host of "transformist" arguments which are put forward as irrefutable. Well, I make a present of my deductive theory to whosoever desires it, and without the least regret; I do not believe a single word of it, and I confess my profound ignorance of the origin of the twofold system of diet.
One thing I do see more clearly after all my experiments and research: the tactics of the Philanthus. As a witness of its ferocious feasting, the true motive of which was unknown to me, I treated it to all the unfavourable epithets I could think of; called it assassin, bandit, pirate, robber of the dead. Ignorance is always abusive; the man who does not know is full of violent affirmations and malign interpretations. Undeceived by the facts, I hasten to apologise and express my esteem for the Philanthus. In emptying the stomach of the bee the mother is performing the most praiseworthy of all duties; she is guarding her family against poison. If she sometimes kills on her own account and abandons the body after exhausting it of honey, I dare not call her action a crime. When the habit has once been formed of emptying the bee's crop for the best of motives, the temptation is great to do so with no other excuse than hunger. Moreover—who can say?—perhaps there is always some afterthought that the larvæ might profit by the sacrifice. Although not carried into effect the intention excuses the act.
I therefore withdraw my abusive epithets in order to express my admiration of the creature's maternal logic. Honey would be harmful to the grubs. How does the mother know that honey, in which she herself delights, is noxious to her young? To this question our knowledge has no reply. But honey, as we have seen, would endanger the lives of the grubs. The bees must therefore be emptied of honey before they are fed to them. The process must be effected without wounding the victim, for the larva must receive the latter fresh and moist; and this would be impracticable if the insect were paralysed on account of the natural resistance of the organs. The bee must therefore be killed outright instead of being paralysed, otherwise the honey could not be removed. Instantaneous death can be assured only by a lesion of the primordial centre of life. The sting must therefore pierce the cervical ganglions; the centre of innervation upon which the rest of the organism is dependent. This can only be reached in one way: through the neck. Here it is that the sting will be inserted; and here it is inserted in a breach in the armour no larger than a pin's head. Suppress a single link of this closely knit chain, and the Philanthus reared upon the flesh of bees becomes an impossibility.
That honey is fatal to larvæ is a fact pregnant with consequences. Various predatory insects feed their young with honey-makers. Such, to my knowledge, are the Philanthus coronatus, Fabr., which stores its burrows with the large Halictus; the Philanthus raptor, Lep., which chases all the smaller Halictus indifferently, being itself a small insect; the Cerceris ornata, Fabr., which also kills Halictus; and the Polaris flavipes, Fabr., which by a strange eclecticism fills its cells with specimens of most of the Hymenoptera which are not beyond its powers. What do these four huntresses, and others of similar habits, do with their victims when the crops of the latter are full of honey? They must follow the example of the Philanthus or their offspring would perish; they must squeeze and manipulate the dead bee until it yields up its honey. Everything goes to prove as much; but for the actual observation of what would be a notable proof of my theory I must trust to the future.