Every one must have observed that these large caterpillars have a sort of uncanny, poisonous appearance; that they suggest a small, thick snake or other evil beast, and the eyes do much to increase the deception. Moreover, the segment on which they are placed is swollen, and the insect, when in danger, has the habit of retracting its head and front segments, which gives it an additional resemblance to some small reptile. That small birds are, as a matter of fact, afraid of these caterpillars (which, however, I need not say, are in reality altogether harmless) Weissmann has proved by actual experiment. He put a caterpillar in a tray in which he was accustomed to place seed for birds. Soon a little flock of sparrows and other small birds assembled to feed as usual. One of them lit on the edge of this tray, and was just going to hop in, when she spied the caterpillar. Immediately she began bobbing her head up and down, but was afraid to go nearer. Another joined her, and then another, until at last there was a little company of ten or twelve birds, all looking on in astonishment, but not one ventured into the tray, while one which lit in it unsuspectingly beat a hasty retreat in evident alarm as soon as she perceived the caterpillar. After watching for some time, Weissmann removed the caterpillar, when the birds soon attacked the seeds. (Journal of the Society of Arts, February 23, 1877, p. 284.)
When Shakespeare said that all the world was a stage, and men and women merely players, he never thought, probably, that the remark might be extended, and that many a good comedy — though a comedy of which there are too frequently no intelligent spectators — is acted in spheres far beneath the human. This hawk-moth caterpillar, with the mock-terrors of its mock-eyes, keeping a dozen little birds at bay by merely wriggling beneath its uncomely mask of fear, was surely as remarkable an actor, as skilful a player on nervous fears, as ever turned the threatenings of tragedy into comedy by an improvised impersonation.
It is somewhat remarkable that these protective illusions, though they take effect through the impression they produce on higher organizations, like the organization of birds, are much seldomer found to be protective of such organizations than of the lower organizations of reptiles and insects. It is only while positive resources are wanting that these negative resources for the protection of creatures preyed on by higher animals, are used. The reptile and the insect are protected by their resemblance either to the vegetation they are habitually found amongst, or to other creatures which are more dangerous than they. But the deceived are not protected so elaborately as the deceivers. The sparrows which were so alarmed by the sphinx caterpillars, though they were not acute enough to see through the illusion, were far superior in intelligence to the creature which gained by the illusion; and partly no doubt for that reason, they are not protected from their enemies by the same kind of artifices. These elaborate artifices are the rudest resorts of nature for the protection of life, not the most advanced. As organization becomes more complex, and resources of all kinds open, the hypocrisy of nature begins to play a less important part, and is, indeed, pretty nearly confined to wrapping otherwise dangerously exposed lives in cloaks of a color so like that of their environment, that they are unconspicuous, and pass without notice, — just as the plumage of certain birds, for instance, in bare countries, conforms itself to the summer or winter hue of the ground they frequent.
Still, true as this is, it is certain that the hypocrisies of nature repeat themselves with more or less completeness and consciousness in the mental life of man. What is the vast force exerted by habit in moulding us into the likeness of the society to which we belong, except a device for making us safe by preventing us from being conspicuous, just as the small green caterpillar is made safe and unconspicuous by its resemblance to the color of the leaves on which it feeds? And it is of course, as in the animal world, the most passive of our species in whom this device of nature for veiling the peculiarities of the moral personality, — always in some respects dangerous things, — is applied with the most elaborate success. The "spectre insect," the "walking-stick" insect, the "praying insect," — as the Mantis religiosa is called, from the stiff attitude in which it keeps its forelegs in the air, partly from the instinct which makes it imitate the position of the withered twig, and partly that it may be ready to catch any unwary insect which comes within its grasp, — have all their analogies among the feebler-natured members of our race, amongst the beggars, for instance, who prey upon society while they appear to be merely fixed in attitudes of patient endurance. How closely, for instance, the Mantis religiosa, lying in wait for prey, resembles our pious Bible-readers of the streets, quite unconscious of the halfpence they attract. But is there any human analogy for the harmless snake and the sphinx caterpillar, which
