In August the adults begin to appear outside the seed-pods of the iris. The larva has not the talent which the Pea-weevil’s grub possesses: it does not, by patient nibbling, make any sort of preparation for the exodus. It is the perfect insect itself that contrives the exit-way, which consists of a round hole bored through the tough husk of the seed and the thick wall of the fruit. Finally, in September, the capsules of the iris turn brown and the three valves become unfastened; the house threatens to fall to pieces. Before it becomes untenable, the last occupants hasten to clear out, each by its round window. They will spend the winter in the neighbourhood, under some kind of shelter; then, when spring returns and the iris is yellow with flowers, the colonizing of the capsules will begin all over again.
The flora of my district, not far from the spots frequented by our insect, in addition to the yellow iris comprises three other species. On the neighbouring hills, among the rock-roses and the rosemaries, the dwarf iris abounds (I. chamæiris, Bertol.), with flowers of varying colour: they [[242]]are sometimes purple, sometimes yellow or white and sometimes attired in a mixture of the three hues. The plant is barely a hand’s-breadth in height, but its flowers are quite as large as those of the other species.
On the same hills, at points where the rains have left a little moisture, the spurious iris (I. spuria) forms a glorious carpet. It is tall, slender-leaved and decked with flowers of rare beauty. Lastly, near the brook where I have been observing the Iris-weevil, is the Gladwyn iris, or leg-of-mutton iris (I. fœtidissiina, Lin.), whose leaves, when bruised, give a faint scent of mutton and garlic. Its seeds are a fine orange-red, a specific characteristic which recurs not elsewhere.
Altogether, without counting such foreigners as may have found their way into the flower-gardens around, we see four varieties of native iris at the Weevil’s disposal. They have the same sort of capsules, all equally bulky and equally rich in seeds, whose properties as food cannot differ much. Moreover the four plants flower at the same season. And of these four, which would permit her greatly to extend her race, the Weevil invariably selects the yellow iris. I have never found the insect established in the capsules of one of the other three.
For what reasons does she prefer niggardly uniformity to varied abundance? The tastes of the adult insect and those of the larva must have [[243]]something to say to the choice. The adult feeds on the fleshy hull of the capsules; the grub, on the other hand, lives entirely on the seeds, which are not yet hardened and are full of juice. Are the appetites of the adult insect satisfied with the fruit of any kind of iris? This can be tested.
Under the trellis-work of a wire cover, I place before the Weevil some green capsules of different origins. Jumbled up with the fruits of the yellow iris are those of the dwarf iris, the leg-of-mutton iris and the spurious iris. To these I add some foreign capsules, those of the pale Turkey iris (I. pallida, Lam.) and of the great bulbous iris (I. xiphoides, Ehrh.), which differs so greatly from the others by the bulb which takes the place of the usual rhizome.
Well, all these fruits are accepted as eagerly as those of the yellow iris. The Weevil riddles them with punctures, strips them bare, pierces them with windows. The capsules of my choosing and those from the banks of the stream, which are normally used, often lie side by side; the consumer makes no distinction between them, but goes without hesitation from one to the other, attacking them with a zeal which is in no wise impaired by the novelty of the dish. It considers everything good to eat, so long as it comes from an iris of some sort or other.
And this is not, as one might reasonably suppose, [[244]]an aberration caused by the tedium of captivity. I have found in the harmas[1] on the tall stalks of the pale Turkey iris, a group of our Weevils feeding together on the green capsules. Whence came they, these pilgrims observed for the first time between my four walls? How did they learn, these colonists from the moist river-banks, that an iris which provided excellent eating was flowering amid the aridities of my acre of pebbles? At any rate, they left no part of the young capsules intact. The food discovered suited them very well. It was therefore impossible for me to profit by this windfall in order to ascertain whether the unfamiliar plant would serve for the establishment of the family.
Apart from the genus Iris, are there any other plants, its near botanical relations, whose fruits are accepted? I have vainly tried the trivalvular capsules of the corn-flag (Gladiolus segetum, Gawl.) and the globular capsules of two asphodels (Asphodelus luteus, Lin. and A. cerasiferus, Gay). The Weevil would have none of them. At most she dipped her rostrum into the green capsules of the yellow asphodel, the common Jacob’s staff. She tasted and then moved away. The dish was not to her liking; and hunger was unable to overcome her obstinate disdain. She would die of starvation [[245]]sooner than touch victuals unhallowed by tradition.
It goes without saying that I found nothing in the way of eggs on the corn-flag or the two asphodels. What the insect regards as unfit for its own consumption is a fortiori refused when the grub’s food is concerned. Nor was I any luckier with the various irises which I tried, the yellow iris excepted. Are we to attribute this refusal to the insect’s captivity? No, for the capsules of the yellow iris were colonized fairly well under my wire covers. The fact is that, as soon as the establishment of the family comes into question, the Weevil abstains entirely from anything that is contrary to habit and remains firmly faithful to the laws and customs of the ancients. In short, I have never found the Weevil established elsewhere than in the capsules of the yellow iris, however appetizing the appearance of the others, especially those of the dwarf iris, which are exceedingly fleshy and very numerous in the spring. [[246]]