Really spits, too; for the insect has a gland in its head which ejects, at need, an irritating fluid. If this fluid gets into your eyes, they smart most unpleasantly. It contains formic acid, and is strong enough to be exceedingly stinging and painful. The discharge repels lizards, and probably also birds, who are among the chief enemies of this as of other caterpillars.
The deadliest foe of the Puss Moth larva, however, is the ichneumon-fly, a parasitic creature, which lays its eggs in living caterpillars, and lets its grubs hatch out inside them, so as to devour the host from within in the most ruthless fashion. There are many kinds of ichneumon-fly, some of them very minute: the one which attacks the Puss Moth in its larval stage is a comparatively big one. The fly lays its eggs behind the caterpillar's head, where the victim is powerless to dislodge them. In all probability the defensive attitude and the shower of formic acid are chiefly of use against these parasitic foes: for when an ichneumon-fly appears, the caterpillar assumes his "terrifying" attitude the moment it touches him, and faces full round to the foe with his false mask inflated. A very small quantity of the formic acid Professor Poulton found sufficient to kill an ichneumon: and there can be little doubt that this is its main object.
9.—CATERPILLARS OF THE LOBSTER MOTH DEMONSTRATING IN FORCE BEFORE THE HOSTILE BATTALIONS.
The last of these "bluffing" caterpillars with which I shall deal here is that of the Lobster Moth. In No. 9 you see a couple of these quaint and unwieldy creatures "demonstrating" before an enemy, as if he were the Sultan. The Lobster Moth in its larval stage frequents beech-trees, and you will see in the illustration that the two represented are on a twig of beech. When at rest, the caterpillar resembles a curled and withered beech-leaf, and by this unconscious mimicry escapes detection. But when discovered and roused to battle, oh, then he imitates the action of the spider. He holds up his short front legs in a menacing attitude, so as to suggest a pair of frightful gaping jaws: the four long legs behind these he keeps wide apart and makes them quiver with rage in the most alarming pantomimic indignation. His tail he turns topsy-turvy over his head like a scorpion; while the forked appendages at its end seem like frightful stings, with which he is just about to inflict condign punishment on whoever has dared to disturb his quiet. But it is all mere brag, though the whole effect is extremely terrifying. The performance does not, indeed, mimic any particular venomous beast, but it suggests most appalling and paralyzing possibilities. Many of these queer attitudes, indeed, owe their impressiveness just to their grotesque simulation of one knows not quite what: they are not definite and special, they are worse than that; they appeal to the imagination. And if only you reflect how afraid we often feel of the most harmless insects, merely because they look frightful, you will readily understand that such vague appeals to the imagination may be far more effectual than any real sting could ever be. We dread the unknown even more than the painful.
The funniest of all these false pretences, however, is one which Hermann Müller, I believe, was the first to point out in this same Lobster Moth caterpillar. When very much bothered by ichneumon-flies (to whose attacks it is particularly exposed), this bristling beast displays, for the first time, two black patches on its side, till then concealed by a triangular flap. Now, these patches closely resemble the sort of wound made by the ichneumon when it deposits its eggs, so it is probable that they serve to take in the assailant, who is thus led to think that another fly of her own kind has been before her, and, therefore, that it is no use laying her eggs where a previous parasite is already in possession. There would not be enough Lobster Moth to feed two hungry ichneumon families. In fact, the caterpillar first begins by bluffing, and says, "If you touch me, I bite!" then, finding the bluff unsuccessful, it further pretends to throw up the sponge, and cries out with a bounce: "Oh, if egg-laying is your game, that's no good: I'm already occupied!" For a combination of wiles, this crafty double game probably "licks creation."
If the defenders are so cunning, however, the attackers can sometimes turn the tables upon them. Animals that hunt often disguise themselves, in order to avoid the notice of the prey, and so steal unobserved upon their victims. Such tactics are like those of the Kaffirs, who cut bits of bush, and then creep up slowly, slowly behind them, under cover of the branches, upon the gnus or antelopes which they wish to slaughter. In No. 10 we have one example of this method of hunting or stalking, as pursued by the intelligent English grass-spider. All spiders, of course, have eight legs, four on each side; but in most of the class, the various pairs of legs are evenly distributed, so as to lie about the body in a rough circle or something like it. The grass-spider, however, has his own views on this important matter. His form and attitude are quite peculiar. He lies in wait for his prey on the open, crouched against a stem of grass, with his two front pairs of legs extended before him, and his back pair behind, in an arrangement which is rather linear than circular. This position makes him almost invisible—much more invisible in real life, indeed, than you see him in the drawing; for if he were represented as inconspicuous as he looks you would say there was no spider there at all, only a naked grass-stem. The delusion is heightened by his lines and colours: he is mostly green or greenish, with narrow black or brown stripes which run more or less up and down his body, instead of cross-wise as usual, so that they harmonize beautifully with the up-and-down lines of the blades and stem in the tuft which he inhabits. When he is pressed close against a bent of grass, on the look-out for flies, it is almost impossible for the quickest eye to distinguish him. Flies come near, never suspecting the presence of their hereditary foe; as soon as they are close to him, the grass-spider rushes out with a dash and secures them. His jaws are among the most terrible in all his terrible race: they are large and wide-spreading, with two rows of teeth on either side, and a pair of long fangs of truly formidable proportions.
10.—GRASS-SPIDER, IN AMBUSH FOR FLIES.
In other ways, also, this particular spider is a clever fellow, for he lives near water; but when the rains are heavy and there is likely to be a flood, he shifts his quarters higher up the ground, and so escapes impending inundation.