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Show 210 MR. E. B. POULTON ON THE PROTECTIVE [Mar. 1, distasteful species are carefully excluded from the diet. Thus Butterflies and Moths are freely eaten by Lizards (see Appendices) ; but I am sure that they are not really enjoyed in the same way as when a Housefly or a palatable Caterpillar is offered to them. This is doubtless because the imagos of Lepidoptera are dusty, unsatisfactory things to eat, with such a small proportion of body in which the real nutriment and taste is contained, and so large an expanse due to tbe dry membranous wings with their scaly covering. In this respect the Butterflies contrast unfavourably (as food) with the Moths, and the latter are certainly preferred (when both are palatable in other ways). The same preference is manifested by Frogs (Hyla arborea) with even greater force ; there is a most extraordinary difference in the behaviour of such a Frog in the presence of a Housefly or of a Butterfly respectively, and in fact the latter is often disregarded. Of course birds are in a different position as regards such insect-food, for they at an)7 rate very generally pick off the unpalatable parts before eating a lepidopterous imago (Jenner Weir) ; and with them it is common to witness all the signs of an intense desire for these insects, especially Moths. Birds can similarly largely remove the unpleasantness due to larval hairs, as was seen in the case of O. antiqua (Table 1.). W e should doubtless see evidence for the existence of such nice discrimination between the relative payabilities of various insects, in the case of all insect-eaters, if our observations were sufficiently numerous and minute; but it must be quite clear that the preferences cannot be always satisfied, when we remember the extent and keenness of competition. In this country it is hard to realize the excessive abundance of reptile life, chiefly among the Lizards, which obtains even so near to us as tbe south of Europe, and which almost entirely depends upon the insect fauna for food. Almost every step along an Italian road startles several Lizards on the road-side wall or bank ; and it must be perfectly clear that under such circumstances it is quite impossible for all to be served with the food which is most appreciated. W e see rather the very conditions which must render the acquisition of an unpleasant taste together with the correlative "warning" colours, an exceedingly hazardous mode of protection, if assumed by more than a small proportion of the species constituting the insect fauna of such a country. For in so great a press of competition among the innumerable insect-eaters, we may feel sure that some at least would be sufficiently enterprising to make the best of unpleasant food, which has at least the advantage of being easilv seen and caught. And such a conclusion will, I think, be confirmed by a study of the tabulated details. It must be admitted that Wallace's suggestion, with its experimental proof, has taken a most important place among the principles which deal with the infinitely complex and ever-changing relations which obtain between tbe most widely separated no less than between the most allied members of the organic kingdom. But it is no less true that the principle carries with it its own compensating principle, which will come into operation precisely as the former advances to the possession |
