Fig. 32.—Daddy Longlegs (Tipula oleracea).
Other species of small Tipulæ have aquatic larvæ very similar to those which we have described. Réaumur remarked that each of these worms is lodged in a thick mass, convex at the top, formed of a transparent and adhesive white jelly. The larvæ of the larger Tipulæ are not aquatic, but are of different habits, and live under the ground; all soil which is not frequently turned is suitable to them, but they are to be found especially in low damp meadows.
Réaumur saw large districts of grassy swamps in Poictou, which, in certain years, furnished very little grass for the cattle, on account of the ravages caused by these larvæ. They had also much injured the harvest in the same districts during those years.
These larvæ appear to require no other food than vegetable mould. Their excrements are, in fact, according to Réaumur, nothing else than dried earth, from which the stomach and intestines of the insect have withdrawn all nourishing matter.
Old trees have often hollow cavities occasioned by the decay of the trunk. When these cavities are old, their lower parts are full of a sort of mould, which is in fact half-decayed wood. It is there that the Tipulæ often lay their eggs. Réaumur frequently found the larvæ in the trunks of elms or willows, and also in the fleshy parts of certain kinds of mushrooms. He carefully observed the habits of one, which lived under the covering of a mushroom, the Oak agaric (Agaricus quercinus). This larva is round, grey, and resembles an earth-worm. It does not walk, but crawls; and the places where it stops, or which it passes over, are covered with a sort of brilliant slime, like that left by the snail or slug.
M. Guérin-Méneville has published some very interesting remarks on the migrations of the larvæ of a particular kind of Tipula, known by the name of Sciara. We will borrow from that entomologist the following curious details, which will initiate us into one of the most wonderful phenomena in the whole history of insects. These small larvæ are without feet, hardly five lines in length, and about the third of a line in diameter. They are composed of thirteen segments, and have small black heads.
In some years, during the month of July, may be found on the borders of forests in Norway and Hanover, immense trains of these larvæ, formed by the union of an innumerable quantity fixed to each other by a sticky substance. These collections of larvæ resemble some sort of strange animal of serpent-like form, several feet long, one or two inches in thickness, and formed by the union of an immense number, which cling to each other by thousands, and move on together. The whole society advances thus with one accord, leaving a track after it on the ground, as a material indication of its presence.
These strange collections of living creatures form societies, sometimes only a few yards long; but at other times it happens that they form bands from ten to twelve yards in length, of the breadth of a hand and the thickness of a thumb. M. Guérin-Méneville observed columns as many as thirty yards in length. These troops advance as slowly as a snail, and in a certain direction. If they encounter an obstacle—as a stone, for instance—they cross over it, turn round it, or else divide into two sections, which reunite after the obstacle is passed. If a portion of the column be removed so as to divide it into two parts, it is quickly reunited, as the hindmost portion soon joins that which precedes it. Lastly, if the posterior part of this living ribbon be brought into contact with the anterior, a circle is formed, which turns round and round on the same ground for a long time, sometimes even for a whole day, before breaking, and continuing to advance. They are never met with in bad weather, but only when the sun is warm.
The curious and astonishing phenomenon of an assembly of larvæ without feet, advancing with an equal movement resulting from the individual motion of thousands of little worms, was remarked for the first time, in 1603, by Gaspard Schwenefelt. This naturalist says that the inhabitants of Siberia consider this phenomenon as an indication of a bad harvest if they go towards the mountains; whereas, if they descend towards the plains, it is the sign of a good one. In 1715 Jonas Ramus mentioned the same phenomenon, recalling a superstition attached to it by the peasants of Norway. This writer informs us that the peasants of that country, on meeting one of these moving columns, throw down their belts or waistcoats on the ground before it. If the orme-drag (that is the name given to the moving column) crosses over this obstacle, it is a good sign; but on the other hand, if the column turns round the obstacle, instead of crossing it, some mischief may be expected.