Four species live here, thriving admirably, despite the annoyance which my curiosity causes them. The most numerous is the Metallic Cetonia (C. metallica, Fab.). This is the insect that provides me with the greater part of my data. The others are the common Golden Cetonia, or Rose-chafer (C. aurata, Linn.), the Dark-brown Cetonia (C. morio, Fab.) and lastly the small Funeral-pall Cetonia (C. stictica, Linn.).[9]
Let us inspect the heap about nine or ten o’clock in the morning. We must be diligent and patient, for the advent of the laying mothers is subject to capricious delays [[16]]and often makes us wait in vain. Chance favours us. Here is a Metallic Cetonia dropping in from some neighbouring spot. In wide circles she flies once or twice over the heap; she inspects the lie of the land from above and selects a point easy of access. Whoosh! She pounces upon it, digs with her head and legs and forthwith makes her way in. Which way will she go?
At first the sense of hearing tells us of the direction followed: we hear a rustling of withered leaves as long as the insect is working through the dry outer layer. Then nothing but silence: the Cetonia has reached the moist centre of the heap. Here and here only must the laying take place, so that the grub emerging from the egg may find soft food at hand without seeking for it. Let us leave the mother to her task and return a couple of hours later.
But first let us reflect upon what has just occurred. A magnificent insect, a living gem of goldsmith’s work, was slumbering just now at the heart of a rose, on the satin of its petals, in the sweetness of its scent. And now this voluptuary in her golden tunic, this sipper of ambrosia, suddenly leaves her flower and buries herself in corruption; she [[17]]abandons the sumptuous hammock, fragrant of attar, to burrow in nauseous filth. Whence this sudden depravity?
She knows that her grub will regale itself on what she herself abhors; and overcoming her repugnance, not even giving it a thought, she takes the plunge. Is she actuated by the memory of her larval days? But what memory of food can she have after a year’s interval, above all after an absolute remoulding of her organism? To draw the Cetonia hither, to make her come from the rose to this putrid heap, there is something better than the memory of the belly; there is a blind, irresistible impulse, which acts in the most logical manner under cover of a seeming insanity.
Let us now return to the heap of leaf-mould. The rustle of the withered leaves has informed us approximately: we know in what direction to make our search, a minute and hesitating search, for we have to follow the mother’s trail. Nevertheless, guided by the materials thrust aside on the insect’s passage, we reach our goal. The eggs are found, scattered without order, always singly, with no preparatory measures. It is enough that there should be close at hand [[18]]soft vegetable matter, suitably fermented.
The egg is an ivory globule, departing only slightly from the spherical form and measuring nearly three millimetres[10] in diameter. The hatching takes place twelve days later. The grub is white, bristling with short, sparse hairs. When laid bare and removed from its leaf-mould, it crawls upon its back, that is to say, it possesses the curious method of locomotion characteristic of its race. With its earliest wriggles it proclaims the art of walking on its back, with its legs in the air.
Nothing is easier than to rear this grub. A thin box, which hinders evaporation and keeps the provisions fresh, receives the nursling together with a selection of fermented leaves, gathered from the heap of mould. This is enough: my charge thrives and undergoes its transformation in the following year, provided I take care to renew the victuals from time to time. No entomological rearing gives less trouble than that of the Cetonia-larva, with its robust appetite and its vigorous constitution.
Its growth is rapid. At the beginning of August, four weeks after hatching, the grub [[19]]has reached half its final size. The idea occurs to me to estimate its consumption of food by means of the stercoral granules which collect in the box from the time of its first mouthful. I find, 11,978 cubic millimetres;[11] that is to say, in one month the grub has digested a volume of matter equivalent to several thousand times its own initial bulk.
The Cetonia-grub is a mill that is always grinding dead vegetable substances into meal; it is a crushing-machine of great efficiency, which night and day, almost all the year round, shreds and powders the matter which fermentation has already reduced to tatters. In the rotting heap the fibres and veins of the leaves would remain intact indefinitely. The grub takes possession of these refractory remnants; with its excellent shears it tears and minces them very small; it dissolves them, reducing them to a paste in the intestines, and adds them, henceforth capable of being used, to the riches of the soil.