Nest of Willow-leaf Roller.
A caterpillar which feeds upon the willow, and whose singular attitudes have obtained for it the trivial name of Ziczac, also constructs for itself an arbour of the leaves, by drawing them together in an ingenious manner. M. Roesel[BK] has given a tolerable representation of this nest, and of the caterpillar. The caterpillar is found in June; and the moth (Notodonta ziczac) from May to July in the following year (see cut, [p. 151]).
Beside those caterpillars which live solitary in the folds of a leaf, there are others which associate, employing their united powers to draw the leaves of the plants they feed upon into a covering for their common protection. Among these we may mention the caterpillar of a small butterfly, the plantain or Glanville fritillary (Melitea cinxia), which is very scarce in this country.
Ziczac Caterpillar and Nest.
Although a colony of these caterpillars is not numerous, seldom amounting to a hundred individuals, the place which they have selected is not hard to discover. Their abode may be seen in the meadow in form of a tuft of herbage covered with a white web, which may readily be mistaken, at first view, for that of a spider, but closer inspection soon corrects this notion. It is, in fact, a sort of common tent, in which the whole brood lives, eats, and undergoes the usual transformations. The shape of this tent, for the most part, approaches the pyramidal, though that depends much upon the natural growth of the herbage which composes it. The interior is divided into compartments formed by the union of several small tents, as it were, to which others have been from time to time added according to the necessities of the community.
When they have devoured all the leaves, or at least those which are most tender and succulent, they abandon their first camp, and construct another contiguous to it under a tuft of fresh leaves. Several of these encampments may sometimes be seen within the distance of a foot or two, when they can find plantain (Plantago lanceolata) fit for their purpose; but though they prefer this plant, they content themselves with grass if it is not to be procured.
When they are about to cast their skins, but particularly when they perceive the approach of winter, they construct a more durable apartment in the interior of their principal tent. The ordinary web is thin and semi-transparent, permitting the leaves to be seen through it; but their winter canvas, if we may call it so, is thick, strong, and quite opaque, forming a sort of circular hall without any partition, where the whole community lie coiled up and huddled together.
Early in spring they issue forth in search of fresh food, and again construct tents to protect them from cold and rain, and from the mid-day sun.
M. Réaumur found upon trial, that it was not only the caterpillars hatched from the eggs of the same mother which would unite in constructing the common tent; for different broods, when put together, worked in the same social and harmonious manner. We ourselves ascertained, during the present summer (1829), that this principle of sociality is not confined to the same species, nor even to the same genus. The experiment which we tried was to confine two broods of different species to the same branch, by placing it in a glass of water to prevent their escape. The caterpillars which we experimented on were several broods of the brown-tail moth (Porthesia auriflua) and the lackey (Clisiocampa neustria). These we found to work with as much industry and harmony in constructing the common tent as if they had been at liberty on their native trees; and when the lackeys encountered the brown-tails they manifested no alarm nor uneasiness, but passed over the backs of one another, as if they had made only a portion of the branch. In none of their operations did they seem to be subject to any discipline, each individual appearing to work, in perfecting the structure, from individual instinct, in the same manner as was remarked by M. Huber in the case of the hive-bees. In making such experiments, it is obvious that the species of caterpillars experimented with must feed upon the same sort of plant.[BL] (J. R.)