Caterpillars are usually coloured grey or brown, so as to be inconspicuous; but numerous exceptions occur which are brightly coloured, and of these individuals many have been experimentally proved to be objectionable as food to most insect-eating animals, being either protected by an unpleasant taste, or covered with hairs or spines. Familiar cases are those of the abundant and conspicuous black and yellow mottled caterpillars of the European Buff-tip Moth (_Pygæra bucephala_), which are much disliked by birds; and the gaily—coloured Vapourer Moth caterpillar (_Orgyia antiqua_), with its conspicuous tufts of hair. Readers will remember that a few years back these caterpillars were a perfect plague in London, in spite of the abundance of sparrows, which feed freely on smooth green and brown caterpillars. Oft-cited examples of warning colouration, are the three great groups of mainly tropical butterflies—the _Heliconidæ_ of America, the _Acræidæ_ of Africa, and the _Danainæ_ found all over the world. In all of these the sexes are alike. They are, every one, strikingly coloured, displaying patterns of black and red, chestnut, yellow, or white. In most butterflies the lower surface of the wings is of a quiet hue, in order to render the organism inconspicuous when at rest, but in these warningly coloured groups the under surface of the wings is as gaudy as the upper surface. Their flight is slow. They are tough, and exhale a characteristic odour. Belt showed that, in Nicaragua, birds, dragonflies, and lizards seem to avoid the Heliconine butterflies, as the wings of these last are not found lying about in places where insectivorous creatures feed, whereas wings of the edible forms are to be found. Moreover, a Capuchin monkey, kept by Belt, always refused to eat Heliconine butterflies. Finn investigated the palatability of a number of Indian insects. He found that most of the birds with which he experimented objected to the Danaine butterflies; but they disliked still more intensely two butterflies belonging to groups not universally protected—a swallowtail (_Papilio aristolochiæ_) and a white (_Delias eucharis_). Finn further experimented with the tree-shrew or Tupaia (_Tupaia ellioti_), which feeds largely on insects. He found that this creature refused most emphatically all these warningly-coloured butterflies. It would under no circumstances eat the _Danainæ_, whereas the birds would do so if no more palatable insects were offered to them at the time. Colonel A. Alcock found that a tame Himalayan bear indignantly refused to eat a locust (_Aularches militaris_) gaily coloured with black, red, and yellow, and exhaling an unpleasant-smelling froth; but this bear readily devoured ordinary brown or green species. Among cold-blooded vertebrates the common European salamander, with its bright black and yellow markings, is a striking example of warning colouration; its skin exudes, on pressure, a very poisonous secretion.