Can this be a temporary distraction, a blunder due to the Wasp’s excessive eagerness for work? She will change her mind, no doubt, perceive her mistake and discontinue her futile labours. But no: I see her coming back thirty times in succession. At each trip she brings a globule of mud, which she applies, without making a single error, inside the circumference formed by the line of clay which the base of the nest has left on the wall. Her memory, which tells her nothing of the colour, shape or prominence of the nest, is surprisingly faithful in matters of topographical detail: it knows nothing of essentials but is thoroughly acquainted with accessories; topographically speaking, the nest is there; the structure, it is true, is missing, but there is the supporting base; and that, it appears, is enough; at any rate, the Pelopæus is lavish of her exertions in bringing mud to plaster the surface on which the structure no longer stands.
In the old days, the Mason-bees used to [[116]]surprise me greatly with their tenacious memory of the spot where the pebble lay supporting their nest and with their lack of perspicacity in all that concerned the nest itself, which was replaced by another, quite different nest without making them interrupt the work already begun. The Pelopæus outdoes them in these aberrations: she gives the last strokes of the trowel to an imaginary dwelling, of which nothing but the site remains.
Has she, as a matter of fact, a more obtuse intellect than the dome-builder? The entomological tribe seems hardly to swerve from a common stock of aptitudes; those whom we consider the most richly endowed, on the evidence of actions normally accomplished, show themselves as limited as the rest when the experimenter disturbs the current of their instincts. It is probable that the Mason-bee would have committed the same absurdities as the Pelopæus, had I thought of subjecting her, at a propitious time, to a similar test. A plasterer by profession, she would, like the other, have plastered the base of the nest removed from the pebble at the right moment. My confidence in the glimmer of reason which the makers of theories attribute to the animal [[117]]is so greatly shaken that I do not regard my unflattering opinion of the Mason-bee as rash.
Thirty times, I said, in my presence did the artist in earthenware lay and then spread her pellet of mud upon the bare wall, thinking that she was applying it to the nest itself. Sufficiently informed by this long perseverance, I left the Pelopæus still busy at her futile task. Two days later, I inspected the plastered site. The coating of mud did not differ from that shown by a finished nest.
I have suggested that the insect’s rudimentary intelligence has practically the same limitations everywhere. The accidental difficulty which one insect is powerless to overcome, in default of a gleam of judgment, any other, no matter what its genus or species, will be equally unable to overcome. To vary the evidence, I will borrow my next example from the Lepidoptera.[2]
The Great Peacock[3] is the largest Moth of our district. Her caterpillar, which is yellow-hued, with turquoise-blue spots surrounded [[118]]by black hairs, spins itself, at the foot of the almond-trees, a robust cocoon whose ingenious construction has long been celebrated. At the moment of her deliverance, the Mulberry Bombyx[4] has in her stomach a particular solvent which the new-born Moth disgorges against the wall of the cocoon to soften it, to dissolve the gum that sticks the threads together and in this way to force an exit by the mere pressure of her head. With the aid of this reagent, the recluse is able triumphantly to attack her silken prison at the fore-end, the rear-end or the side, as I discover by turning the chrysalis in its cocoon, which I slit with a pair of scissors and then sew up again. Whatever the spot to be perforated for the emergence, a spot which my intervention varies at will, the liquid disgorged promptly soaks into and softens the wall, whereupon the captive, struggling with her fore-limbs and pushing her forehead against the tangle of unstuck threads, makes herself a passage with the same ease as in her natural liberation.
The Great Peacock is not endowed with this method of delivery by means of a solvent; [[119]]her stomach is incapable of preparing the corrosive calculated to destroy, at any point, the defensive enclosure which is now a prison-wall. Indeed, if I reverse the chrysalis in its cocoon, opened and then closed with a few stitches, the Moth always dies, being powerless to free herself. When the point to be forced is changed, the release becomes impossible. To emerge from this shell, a genuine strong-box, a special method is therefore necessary, one having no relation to the chemical method of the Mulberry Bombyx. Let me describe, as others have done before me, how things happen.
At the fore-end of the cocoon, a conical end, whereas the other is rounded, the threads are not glued together; every elsewhere, the silken web is cemented with a gummy product that turns it into a stout, waterproof parchment. Those front threads, which are almost straight, converge at their free end and form a cone-shaped series of palisades, having as their common base the circle where the use of the gummy cement is suddenly discontinued. The arrangement can best be compared with the mouth of an Eel-pot, which the fish readily enters by following the funnel of [[120]]osier-switches, but from which the imprudent one cannot get out again, because the narrow passage closes its palisade at the least effort to push through.
Another very accurate comparison is provided by the Mouse-traps with an entrance consisting of a bunch of wires arranged in a truncated cone. Attracted by the bait, the rodent enters the orifice of the trap, enlarging it with a gentle thrust; but, when it becomes a question of departure, the wires, at first so tractable, become an insuperable barrier of halberds. Both devices permit entrance and forbid exit. If we invert the arrangement of the conical palisade, making it point outwards from within, its action is reversed: exit is permitted and entrance forbidden.
This is the case with the Great Peacock’s cocoon, which has a slight improvement to its credit: its mouth, shaped like the Eel-pot or Mouse-trap aforesaid, is formed of a numerous series of cones, fitting one within the other and overlapping. In order to emerge, the Moth has only to push her head in front of her; the several rows of uncemented threads yield without difficulty. Once the recluse is liberated, these threads resume their position, so that there is nothing [[121]]outside to show whether the cocoon is empty or inhabited.