attack, are very bold and fearless, so that no disguise is necessary in order to approach them. The spiders, on the other hand, are eagerly sought for by insectivorous birds; hence there is little doubt that the mimicry is protective.' FIG. 53.-Synageles picata; an ant-like spider (from Peckham). E. G. Peckham also describes two ant-like spiders in North America. Synageles picata (see fig. 53) is like an ant in form and colour; but by far the most deceptive thing about it is the way in which it moves. It does not jump like the other Attidæ, nor does it walk in a straight line, but zigzags continually from side to side, exactly like an ant which is out in search of booty. . . The ant only moves in this way when it is hunting, at other times it goes in a straight line; but its little imitator zigzags always.' Unlike Mr. Belt's spider, S. picata holds up its second pair of legs to represent antennæ. 'Spiders commonly remain nearly motionless while they are eating; picata, on the other hand, acts like an ant which is engaged in pulling some treasure-trove into pieces convenient for carrying. I have noticed a female picata which, after getting possession of a gnat, kept beating it with her front legs as she ate, pulling it about in different directions, and all the time twitching her ant-like abdomen.' This spider certainly does not molest the 1 Loc. cit. pp. 314, 315. ants it resembles, so that the Mimicry is probably protective. Synemosyna formica (see fig. 54) is even more FIG. 54.-Synemosyna formica, an ant-like spider (from Peckham). like an ant than S. picata; it also holds up its second pair of legs as antennæ, and its walk is described as very different from that of closely allied spiders.' Insects which mimic Vertebrate animals We finally reach the most remarkable cases of Protective Mimicry, in which the defenceless form lives upon the reputation of some dangerous animal belonging to another sub-kingdom. Mr. Bates describes a South American caterpillar which startled him, and everyone to whom he showed it, by its strong resemblance to a snake, and it even possessed the features which are characteristic of a poisonous serpent.2 1 Loc. cit. pp. 110-12. 2 Loc. cit. p. 509. Equally interesting examples are to be found among our British caterpillars. The brown (or occasionally green) mature larva of the Large Elephant Hawk Moth (Charocampa elpenor) generally hides among the dead brown leaves on the older parts of the stem of its food-plant, the Great Willow-herb (Epilobium hirsutum). In this position it is difficult to see, for it harmonises well with the colour of its FIG. 55.-The caterpillar of the Large Elephant Hawk Moth (Charocampa surroundings. It possesses an eye-like mark on each side of two of the body-rings (the first and second abdominal segments); but these markings do not attract special attention when the animal is undisturbed. The appearance of the caterpillar is shown in fig. 55. As soon, however, as the leaves are rustled by an approaching enemy, the caterpillar swiftly draws its head and the three first body-rings into the two next rings, bearing the eye-like marks. These two rings are thus swollen, and look like the head of the animal, upon which four enormous, terrible-looking eyes are prominent. The effect is greatly heightened by the suddenness of the transformation, which endows an innocent-looking and inconspicuous animal with a terrifying and serpent-like appearance. I well re member the start with which I drew back my hand as I was going to take the first specimen of this caterpillar that I had ever seen. The appearance of the closely allied C. porcellus in the alarming attitude is shown in fig. 56. The posterior 'eyes' are insignificant in this species. FIG. 56. The caterpillar of the Small Elephant Hawk Moth (Charocampa porcellus) in its terrifying attitude after being disturbed (from Weismann); stage iv.; about twice natural size. Such caterpillars terrify their enemies by the suggestion of a cobra-like serpent; for the head of a snake is not large, while its eyes are small and not specially conspicuous. The cobra, however, inspires alarm by the large eye-like' spectacles' upon the dilated hood, and thus offers an appropriate model for the swollen anterior end of the caterpillar with its terrifying markings. It is extremely interesting that the caterpillar should thus mimic a feature which is only deceptive in the snake itself. Experimental proofs of the protection afforded by The success of this method of defence depends upon an elaborate system of intimidation. An obvious criticism suggests that this interpretation is too fanciful, and that the appearance must have some other meaning. It is therefore of the highest importance to bring forward direct evidence proving that insecteating animals are actually terrified by such caterpillars. Professor Weismann offered a Large Elephant caterpillar to a tame Jay, which immediately killed and devoured it. His fowls were, however, much awed by the appearance of a larva, although after great deliberation one of them ventured to attack it, when the imposition was of course instantly revealed, and the caterpillar devoured. He then placed one in the seed-trough, and found that the sparrows and chaffinches were effectually kept off by it. One sparrow flew down obliquely, so that the caterpillar was hidden by the side of the trough until the bird was close upon it; the instant the caterpillar was seen, the bird clearly showed its alarm by the sudden manner in which it altered its course.1 Lady Verney also found that small birds would not come near a tray containing breadcrumbs when one of these caterpillars was placed upon it.2 Loc. cit. pp. 330-33. 2 Good Words, 1877, p. 838. |