II. Lizards. In those parts of the world where lizards of larger size are abundant there is plenty of evidence that certain species are very destructive to butterfly life. As might be expected this is especially true of forms which are either arboreal or semi-arboreal in habit. Among the reptiles of Ceylon, for example, are several species of the genus Calotes, of which two, C. ophiomachus and C. versicolor, are particularly abundant. In appearance and habits they are not unlike chameleons though far more active in their movements. Like chameleons, too, they are able to change colour, and the fact that they can assume a brilliant scarlet hue about the head and neck has probably led to their popular name of "blood-suckers." It is not impossible that the assumption of this scarlet coloration may serve as a lure to bring insects within range. These lizards have often been observed to seize and devour butterflies. Moreover, it is a common thing to find butterflies with a large semi-circular patch bitten out of the hind wings, and there is little doubt but that such injuries have been inflicted by lizards. There is, however, no evidence to suggest that they exercise any discrimination in their choice of the butterflies which they attack. This is borne out by their behaviour towards various species offered to them, both when at liberty and when caged. In an ingenious series of experiments Col. Manders brought various butterflies within reach of a Calotes by the help of a fishing-rod and a long line of fine silk, by this means simulating natural conditions as far as possible.
He found that the lizards ate the so-called distasteful forms such as Danais chrysippus, Euploea core, Acraea violae, and Papilio hector, as readily as the presumably more palatable forms[[57]]. In captivity, too, they will take any butterfly as readily as another. Experiments by Finn[[58]] and by the writer[[59]] proved that they ate Danaids, Euploeas, and Papilio aristolochiae without any hesitation so long as the insects were alive and moving. When, too, a mixture of different species, some with and some without warning coloration, was given to them all were eaten, nor was there any discrimination evidenced in the order in which they were taken. The lizard simply took the first that came within reach and went on until the whole lot was devoured, wings and all.
Some experiments by Miss Pritchett on the American lizard Sceleporus floridanus point to the same conclusion[[60]]. She found that it took without hesitation any butterfly offered to it including the presumably distasteful models Danais archippus and Papilio philenor (cf. pp. [45] and [49]). On the other hand, another species of lizard with which Miss Pritchett experimented, Gerrhonotus infernalis, refused all the butterflies offered to it, though it fed freely on Orthopterous insects as well as on spiders and scorpions.
It seems clear from these various observations and
experiments that certain lizards devour butterflies freely, but that they do not exercise any discrimination in the species which they attack. All are caught and devoured indiscriminately, so that in spite of the fact that such lizards are among the most serious enemies of butterflies we cannot suppose them to play any part in establishing a mimetic resemblance.
III. Birds. The relations which exist between butterflies and their bird enemies have for many years been the subject of keen discussion. It is generally recognised that if mimetic resemblances become established through the agency of discriminating enemies those enemies must be birds. Hence those interested in the question of mimicry have for some years past turned their attention to birds more than to the other enemies of butterflies. That many birds systematically feed on butterflies is a fact that does not admit of doubt. It is true that, as Mr Marshall points out in the valuable paper in which he has summarised the evidence[[61]], observations of birds eating butterflies are relatively scanty. Though, as he points out, this is equally true for other groups of insects besides butterflies, bird attacks on butterflies, owing to the conspicuous nature of the victim, are much more likely to attract attention than attacks on other groups. We are still without much information as to the extent to which birds destroy butterflies and as to whether they shew any decided preference for certain species over others. A careful examination of the contents of the
stomachs of large numbers of insectivorous birds in a tropical area would go some way towards deciding the matter, but at present such information is lacking. We have to rely upon the existing observations of birds attacking butterflies in the wild state, and upon certain feeding experiments made with captive birds.
Observations on birds attacking butterflies where mimetic forms occur have been made almost entirely in certain parts of Africa, in India, and in Ceylon. For Africa, Marshall has collected some forty-six observations of which almost half are concerned with Pierines. The remainder include four instances of attacks on species of Acraea, a genus which on the mimicry theory must be regarded as among the most unpalatable of butterflies.
The records from the Indo-Malayan region (principally India and Ceylon) are somewhat more numerous and here again more than one-third of them refer to Pierines. Among the others are records of the distasteful forms Euploea core, E. rafflesii, Acraea violae, and Papilio hector being taken and devoured.
There is one interesting record which seems to suggest that Swinhoe's Bee-Eater (Melittophagus swinhoei) may exercise that discrimination in the butterflies it attacks which is demanded on the mimicry theory. Lt.-Col. Bingham on one occasion in Burma noticed this species hawking butterflies. He records that they took Papilio erithonius, P. sarpedon, Charaxes athamas, Cyrestis thyodamas, and Terias hecabe, and probably also species of the genera Prioneris, Hebomoia (Pierines),