Littell's Living Age/Volume 133/Issue 1718/Processionary Caterpillars
PROCESSIONARY CATERPILLARS.
"While out for a walk the other day we came across a curious incident in natural history. At Cap Martin, about two miles from Mentone, our attention was attracted by something by the roadside which looked at a little distance like a long, thin serpent. At first we thought it best not to go very near, but curiosity prevailed, and upon closer inspection we found it was a long line, consisting of ninety-nine caterpillars, crawling in single file close after one another. Our curiosity led us to remove one from the middle, a little distance from the others, and we found his place was soon filled up; but he crawled back to them and edged his way into the line again. Then we removed the leader: this brought them for a time to a standstill. After a little while they began to move on, and then we put the original leader in his proper place, but this brought them again to a standstill; and from the way they moved their heads from side to side, a great deal of talking seemed to be going on, and they decided their original leader was not fit to lead, and they chose another, while he had to make his way into the line lower down. A little farther on we saw another line of forty-four coming up in the opposite direction, and we were curious to see what would happen when they met, imagining they might perhaps have a fight; but such was not the case: they joined the others by degrees, and so made a much longer line and marched on.
"We have since heard they climb some particular kind of trees, and make their nests in them, which has a very injurious effect, and often kills the trees, unless the branches are cut off which hold the nests." In an interesting little work on "Insect Architecture," published in 1830, mention is made of these social caterpillars, the construction of their nests, and their processionary habits. The writer says: "It is remarkable that, however far they may ramble from their nest, they never fail to find their way back when a shower of rain or nightfall renders shelter necessary. It requires no great shrewdness to discover how they effect this; for by looking closely at their track it will be found that it is carpeted with silk, no individual moving an inch without constructing such a pathway both for the use of his companions and to facilitate his own return. All these caterpillars, therefore, move more or less in processional order, each following the road which the first chance traveller has marked out with his strip of silk carpeting." Further remarks are made of two species "more remarkable than others in the regularity of their processional marchings." "These are found in the south of Europe, but are not indigenous in Britain. The one named by Réaumur the processionary (Cnethocampa processionea) feeds upon the oak; a brood dividing, when newly hatched, into one or more parties of several hundred individuals, which afterwards unite in constructing a common nest, nearly two feet long and from four to six inches in diameter. It is not divided into chambers, but consists of one large hall, so that it is not necessary that there should be more openings than one; and accordingly, when an individual goes out and carpets a path, the whole colony instinctively follow in the same track, though, from the immense population, they are often compelled to march in parallel files from two to six deep. The procession is always headed by a single caterpillar; sometimes the leader is immediately followed by one or two in single file, and sometimes by two abreast. A similar procedure is followed by a species of social caterpillar which feeds on the pine in Savoy and Languedoc, and their nests are not half the size of the preceding; they are more worthy of notice from the strong and excellent quality of their silk, which Réaumur was of opinion might be advantageously manufactured. Their nests consist of more chambers than one, but are furnished with a main entrance, through which the colonists conduct their foraging processions."
The lady whose remarks are recorded above has since written that the species she observeed feeds upon the pine-trees in the neighborhood of Mentone. S. W. U.