That stiletto-thrust represents, though much less scientifically, the prick of the Hunting Wasp’s sting.[1] The latter wants for her offspring a prey now dead, now paralysed: she knows, with the thoroughness of a consummate anatomist, at what points it behoves her to insert her lancet to procure either sudden death or merely a suppression of movement. The Rhynchites requires for hers a leaf rendered flexible, half-alive, in a sense paralysed, which can be easily fashioned into a cylinder; she is perfectly familiar with the little leaf-stalk, the petiole, in which the vessels that disperse the energy of the foliage are gathered in a tiny bundle; and she inserts her drill here, here only and never elsewhere. Thus at one blow, without much trouble, she effects the ruin of the aqueduct. [[117]]Where can the long-nosed insect have learnt her clever trick of draining springs?
The leaf of the poplar is an irregular rhombus, a spear-head whose sides are expanded into pointed wings. The manufacture of the cylinder begins with one of these two lateral corners, the right or the left indifferently.
Despite the hanging posture of the leaf, which makes the upper or lower surface equally easy of access, the insect never fails to take up its position on the upper side. It has its reasons, dictated by the laws of mechanics. The upper surface, which is smooth and more flexible, has to form the inside of the cylinder; the under surface, which has greater elasticity because of its powerful veins, has to occupy the outside. The statics of the small-brained Weevils agrees with that of the scientists.
Watch her at work. She is standing on the line along which the leaf is rolled, with three legs on the part already rolled and the three opposite legs on the part still free. Firmly fixed on both with her claws and tufts, she obtains a purchase with the legs on one side while straining with the legs on the other side. The two halves of the machine alternate as motive powers, so that at one moment the shaped cylinder encroaches on the free leaf and at another the free leaf moves and is applied to the cylinder already formed.
There is nothing regular, however, about these [[118]]alternations, which depend upon circumstances known to the insect alone. Perhaps they merely enable the insect to take a brief rest without suspending a task which does not allow of interruptions. In the same way our two hands mutually relieve each other by taking it in turns to carry a burden.
It is impossible to form an exact image of the difficulties overcome without watching, for hours on end, the obstinate straining of the legs, which tremble with exhaustion and threaten to jeopardize everything should one of them let go at the wrong moment, or without seeing how prudently the leaf-roller refrains from releasing one claw until the five others are firmly anchored. On the one hand are three points of support, on the other three points of traction; and the six points are shifted, one by one, little by little, without for an instant allowing their mechanical system to become relaxed. A single moment of forgetfulness or weariness would cause the refractory leaf to unroll its cylinder and escape from the manipulator’s grasp.
The work is performed, moreover, in an uncomfortable position. The leaf hangs, almost or even quite vertically. Its surface is varnished and as smooth as glass. But the worker is shod accordingly. With her tufted soles, she scales polished and perpendicular surfaces; with her twelve meat-hooks, she grapples the slippery floor. [[119]]
Yet this fine equipment does not rid the operation of all its difficulties. I find it no easy matter to follow the progress through the magnifying-glass. The hands of a watch do not move more slowly. For a long while the insect stands still, at the same point, with its claws firmly fixed: it is waiting for the leaf to take the curve and cease to react. Here, of course, there is no glue to set hard and hold the fresh surfaces stuck together. The stability depends purely on the flexion acquired. And so it is not unusual for the elasticity of the leaf to overcome the worker’s efforts and partly to unroll the more or less complete work. Stubbornly, with the same impassive slowness, the insect begins all over again, putting the unsubjected piece back into its place. No, the Weevil is not one to allow herself to be upset by failure: she knows too well what patience and time can do.
As a rule, the Rhynchites works backwards. When her line is finished, she is careful not to abandon the fold which she has just made in order to return to the starting-point and begin another. The part last folded is not yet sufficiently subdued; if left to itself too soon, it might prove rebellious and flatten out again. The insect therefore continues at this extreme point, which is more exposed than the rest, and then, without letting go, makes her way backwards to the other end, always with patient deliberation. In this manner, an added [[120]]firmness is imparted to the new fold; and the next fold is prepared. At the end of the line, there is a fresh prolonged halt and a fresh move backwards. Even so does the husbandman plough the furrows in alternate directions.
Less frequently, no doubt when the leaf is found to be so limp as to entail no risk, the insect abandons the fold which it has just made, without going over it again conversely, and quickly scrambles back to the starting-point to make another.