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Caterpillars and butterflies often show us a further step in advance in the direction of minute imitation of ordinary surroundings. Dr. Weismann has published a very long and learned memoir, fraught with the best German erudition and prolixity, upon this highly interesting and obscure subject. As English readers, however, not unnaturally object to trudging through a stout volume on the larva of the sphinx moth, conceived in the spirit of those patriarchal ages of Hilpa and Shalum, when man lived to nine hundred and ninety-nine years, and devoted a stray century or so without stint to the work of education, I shall not refer them to Dr. Weismann’s original treatise, as well translated and still further enlarged by Mr. Raphael Meldola, but will present them instead with a brief resume, boiled down and condensed into a patent royal elixir of learning. Your caterpillar, then, runs many serious risks in early life from the annoying persistence of sundry evil-disposed birds, who insist at inconvenient times in picking him off the leaves of gooseberry bushes and other his chosen places of residence. His infant mortality, indeed, is something simply appalling, and it is only by laying the eggs that produce him in enormous quantities that his fond mother the butterfly ever succeeds in rearing on an average two of her brood to replace the imago generation just departed. Accordingly, the caterpillar has been forced by adverse circumstances to assume the most ridiculous and impossible disguises, appearing now in the shape of a leaf or stem, now as a bundle of dark-green pine needles, and now again as a bud or flower, all for the innocent purpose of concealing his whereabouts from the inquisitive gaze of the birds his enemies.

When the caterpillar lives on a plant like a grass, the ribs or veins of which run up and down longitudinally, he is usually striped or streaked with darker lines in the same direction as those on his native foliage. When, on the contrary, he lives upon broader leaves, provided with a midrib and branching veins, his stripes and streaks (not to be out of the fashion) run transversely and obliquely, at exactly the same angle as those of his wonted food-plant. Very often, if you take a green caterpillar of this sort away from his natural surroundings, you will be surprised at the conspicuousness of his pale lilac or mauve markings; surely, you will think to yourself, such very distinct variegation as that must betray him instantly to his watchful enemies. But no; if you replace him gently where you first found him, you will see that the lines exactly harmonise with the joints and shading of his native leaf: they are delicate representations of the soft shadow cast by a rib or vein, and the local colour is precisely what a painter would have had to use in order to produce the corresponding effect. The shadow of yellowish green is, of course, always purplish or lilac. It may at first sight seem surprising that a caterpillar should possess so much artistic sense and dexterity; but then the penalty for bungling or inharmonious work is so very severe as necessarily to stimulate his imitative genius. Birds are for ever hunting him down among the green leaves, and only those caterpillars which effectually deceive them by their admirable imitations can ever hope to survive and become the butterflies who hand on their larval peculiarities to after ages. Need I add that the variations are, of course, unconscious, and that accident in the first place is ultimately answerable for each fresh step in the direction of still closer simulation?

The geometric moths have brown caterpillars, which generally stand erect when at rest on the branches of trees and so resemble small twigs; and, in order that the resemblance may be the more striking, they are often covered with tiny warts which look like buds or knots upon the surface. The larva of that familiar and much-dreaded insect, the death’s-head hawk-moth, feeds as a rule on the foliage of the potato, and its very varied colouring, as Sir John Lubbock has pointed out, so beautifully harmonises with the brown of the earth, the yellow and green of the leaves, and the faint purplish blue of the lurid flowers, that it can only be distinguished when the eye happens accidentally to focus itself exactly upon the spot occupied by the unobtrusive caterpillar. Other larvae which frequent pine trees have their bodies covered with tufts of green hairs that serve to imitate the peculiar pine foliage. One queer little caterpillar, which lives upon the hoary foliage of the sea-buckthorn, has a grey-green body, just like the buckthorn leaves, relieved by a very conspicuous red spot which really represents in size and colour one of the berries that grow around it. Finally the larva of the elephant hawk-moth, which grows to a very large size, has a pair of huge spots that seem like great eyes; and direct experiment establishes the fact that small birds mistake it for a young snake, and stand in terrible awe of it accordingly, though it is in reality a perfectly harmless insect, and also, as I am credibly informed (for I cannot speak upon the point from personal experience), a very tasty and well-flavoured insect, and ‘quite good to eat’ too, says an eminent authority. One of these big snake-like caterpillars once frightened Mr. Bates himself on the banks of the Amazon.