Another circumstance increases my perplexity. Among the capsules which the Weevil seems to have perforated with her rostrum, some contain eggs of an orange yellow, grouped into a single heap of five or six or more. This multiplicity gives us food for reflection. When fully matured, the capsules of the scallop-leaved mullein are small, greatly inferior in size to those of other plants of the same genus. When still very young, green and tender, those containing the eggs are hardly as big as half a grain of wheat. There is not food for so many feasters in so tiny a morsel; there would not be enough for one.
All mothers are provident. The exploiter of the mullein cannot have endowed her six or more nurselings with such scanty possessions. For these various reasons, I doubt at first whether these are [[252]]really the Cionus’ eggs. What follows is not calculated to decrease my hesitation. The orange eggs hatch out, producing grubs which within twenty-four hours abandon their exiguous natal chamber. They emerge through the orifice which has been left open; they spread over the capsule, cropping its down, a pasture sufficient for their first mouthfuls. They descend to the thin little twigs, which they strip of their bark, and gradually move on to the small adjacent leaves, where the banquet is continued. Let us leave them to grow. Their final transformation will tell me that I really have the authentic larva of the Cionus before my eyes.
They are bare, legless grubs, of a uniform pale yellow, excepting the head, which is black, and the first segment of the thorax, which is adorned with two large black spots. They are varnished all over their bodies with a glutinous humour, so much so that they stick to the paint-brush used to collect them and are difficult to shake off. When teased, they emit from the end of their intestine a viscous fluid, apparently the origin of their varnish.
They wander idly over the young twigs, whose bark they gnaw down to the wood; they also browse on the leaves growing from the twigs, which are much smaller than those upon the ground. Having found a good grazing-place, they stay there without moving, curved into a bow and held in [[253]]position by their glue. Their walk is an undulating crawl, based upon the support of their sticky behind. Helpless cripples, but coated with an adhesive varnish, they are firmly enough fixed to resist a shake of the bough that bears them without falling off. When you have no sort of grapnel to hold on by, the idea of clothing yourself in glue, so that you may shift your position without danger of falling, even in a gust of wind, is an original invention of which, as yet, I know no other instance.
Our grubs are easily reared. Placed in a glass jar, with a few tender twigs of the plant that feeds them, they go on browsing for some time and then make themselves a pretty ampulla in which the transformation will take place. To observe this performance and discover the method employed was the chief purpose of my inquiry. I succeeded, though not without a great expenditure of assiduity.
All its life long, the larva is smeared, on both its dorsal and its ventral surface, with a viscous, colourless, strongly adhesive fluid. Touch the creature lightly, anywhere, with the tip of a camel-hair pencil. The glutinous matter yields and draws out into a thread of a certain length. Repeat the touch in the hot sunshine, in very dry weather. The viscosity is not diminished. Our varnishes dry up; the grub’s does not; and this is a property of the greatest value, enabling the feeble larva, without fear of being shrivelled by the wind or [[254]]the rays of the sun, to adhere firmly to its food-plant, which loves the open air and warm, sunny places.
The laboratory producing this sticky varnish is easily discovered; we have only to make the creature move along a slip of glass. We see from time to time a sort of treacly dew oozing from the end of the intestine and lubricating the last segment. The glue is therefore supplied by the digestive canal. Is there a special glandular laboratory there, or is it the intestine itself that prepares the product? I will leave the question unanswered, for nowadays I no longer have the steady hand or the keen sight required for delicate dissection. The fact remains that the grub daubs itself with a glue of which the end of the intestine is at least the storehouse, if it is not the actual source.
How is the sticky emission distributed over the whole body, both above and below? The larva is a legless cripple; it moves about by obtaining a hold with its behind. Moreover, it is well segmented. The back, in particular, has a series of fairly protuberant cushions; the ventral surface, on the other hand, is puckered by knotty excrescences, which change their shape considerably in the act of crawling. When moving, with the flexible fore-part of the body groping to find its way, the grub consists of a series of waves that follow one another in perfect order.
Each wave starts from the hinder extremity [[255]]and by swift degrees reaches the head. Straightway a second wave follows in the same direction, succeeded by a third, a fourth and so on, indefinitely. Each of these waves, proceeding from one end of the grub to the other, is a step. So long as the wave continues, the fulcrum, that is, the orifice of the intestine, remains in its place, at first a little before and then a little behind the movement as a whole. Hence the source of the sticky dew grazes first the tip of the abdomen and then the end of the back of the moving grub. In this way the tiny drop of gum is deposited above and below.
The glue has still to be distributed. This is done by crawling. Between the puckers, the cushions, which the locomotory wave brings together and then separates, alternately come into contact and open clefts into which the sticky fluid gradually makes its way by capillary action. The grub clothes itself in glue without exercising any special skill, merely by moving along. Each locomotory wave, each step, supplies its quota to the viscous doublet. This makes up for the losses which the larva cannot fail to suffer on the road as it roams from pasture to pasture; and, since the fresh material balances the wastage of the old, a suitable coat is obtained, neither too thin nor too thick.