Other Examples of Mimicry among Lepidoptera.

In tropical Asia, and eastward to the Pacific Islands, the Danaidæ take the place of the Heliconidae of America, in their abundance, their conspicuousness, their slow flight, and their being the subjects of mimicry. They exist under three principal forms or genera. The genus Euploa is the most abundant both in species and individuals, and consists of fine broad-winged butterflies of a glossy or metallic blue-black colour, adorned with pure white, or rich blue, or dusky markings situated round the margins of the wings. Danais has generally more lengthened wings, of a semitransparent greenish or a rich brown colour, with radial or marginal pale spots ; while the fine Hestias are of enormous size, of a papery or semitransparent white colour, with dusky or black spots and markings. Each of these groups is mimicked by various species of the genus Papilio, usually with such accuracy that it is impossible to distinguish them on the wing. Several species of Diadema, a genus of butterflies allied to our Vanessas, also mimic species of Danais, but in this case the females only are affected, a subject which will be discussed in another chapter.

1

Another protected group in the Eastern tropics is that of the beautiful day-flying moths forming the family Agaristidæ. These are usually adorned with the most brilliant colours or conspicuous markings, they fly slowly in forests among the butterflies and other diurnal insects, and their great abundance sufficiently indicates their possession of some distastefulness which saves them from attack. Under these conditions we may expect to find other moths which are not so protected imitating them, and this is the case. One of the common and wide-ranging species (Opthalmis lincea), found in the islands from Amboyna to New Ireland, is mimicked in a wonderful manner by one of the Liparida (the family to which our common "tussock" and "vapourer" moths belong). This is a new species collected at Amboyna during the voyage of the Challenger, and has been named Artaxa simulans. Both

1 See Trans. Linn. Soc., vol. xxv. Wallace, on Variation of Malayan Papilionidae; and, Wallace's Contributions to Natural Selection, chaps. iii. and iv., where full details are given.

insects are black, with the apex of the fore wings ochre coloured, and the outer half of the hind wings bright orange. The accompanying woodcuts (for the use of which I am indebted to Mr. John Murray of the Challenger Office) well exhibit their striking resemblance to each other.

FIG. 24.-Opthalmis lincea (Agaristida). Artaxa simulans (Liparida).

In Africa exactly similar phenomena recur, species of Papilio and of Diadema mimicking Danaidæ or Acræide with the most curious accuracy. Mr. Trimen, who studied this subject in South Africa, has recorded eight species or varieties of Diadema, and eight of Papilio, which each mimic some species of Danais; while eight species or varieties of Panopæa (another genus of Nymphalidae), three of Melanitis (Eurytelidae), and two of Papilio, resemble with equal accuracy some species of Acræa. He has also independently observed the main facts on which the explanation of the phenomenon rests, the unpleasant odour of the Danais and Acræa, extending to their larvæ and pupae; their great abundance, slow flight, and disregard of concealment; and he states that while lizards, mantidæ, and dragonflies all hunt butterflies, and the rejected wings are to be found abundantly at some of their

1 See Trans. Linn. Soc., vol. xxvi., with two coloured plates illustrating cases of mimicry.

feeding-places, those of the two genera Danais and Acrea were never among them.

The two groups of the great genus Papilio (the true swallowtailed butterflies) which have been already referred to as having the special characteristics of uneatable insects, have also their imitators in other groups; and thus, the belief in their inedibility-derived mainly from their style of warning coloration and their peculiar habits-is confirmed. In South America, several species of the "Eneas" group of these butterflies are mimicked by Pieridæ and by day-flying moths of the genera Castnia and Pericopis. In the East, Papilio hector, P. diphilus, and P. liris, all belonging to the inedible group, are mimicked by the females of other species of Papilio belonging to very distinct groups; while in Northern India and China, many fine day-flying moths (Epicopeia) have acquired the strange forms and peculiar colours of some of the large inedible Papilios of the same regions.

In North America, the large and handsome Danais archippus, with rich reddish-brown wings, is very common; and it is closely imitated by Limenitis misippus, a butterfly allied to our 66 white admiral," but which has acquired a colour quite distinct from that of the great bulk of its allies. In the same country there is a still more interesting case. The beautiful dark bronzy green butterfly, Papilio philenor, is inedible both in larva and perfect insect, and it is mimicked by the equally dark Limenitis ursula. There is also in the Southern and Western States a dark female form of the yellow Papilio turnus, which in all probability obtains protection from its general resemblance to P. philenor. Mr. W. H. Edwards has found, by extensive experiment, that both the dark and yellow females produce their own kinds, with very few exceptions; and he thinks that the dark form has the advantage in the more open regions and in the prairies, where insectivorous birds abound. But in open country the dark form would be quite as conspicuous as the yellow form, if not more so, so that the resemblance to an inedible species would be there more needed.1

The only probable case of mimicry in this country is that of the moth, Diaphora mendica, whose female only is white, 1 Edwards's Butterflies of North America, second series, part vi.

while the larva is of protective colours, and therefore almost certainly edible. A much more abundant moth, of about the same size and appearing about the same time, is Spilosoma menthrasti, also white, but in this case both it and its larva have been proved to be inedible. The white colour of the female Diaphora, although it must be very conspicuous at night, may, therefore, have been acquired in order to resemble the uneatable Spilosoma, and thus gain some protection.1

Mimicry among Protected (Uneatable) Genera.

Before giving some account of the numerous other cases of warning colours and of mimicry that occur in the animal kingdom, it will be well to notice a curious phenomenon which long puzzled entomologists, but which has at length received a satisfactory explanation.

We have hitherto considered, that mimicry could only occur when a comparatively scarce and much persecuted species obtained protection by its close external resemblance to a much more abundant uneatable species inhabiting its own district; and this rule undoubtedly prevails among the great majority of mimicking species all over the world. But Mr. Bates also found a number of pairs of species of different genera of Heliconidæ, which resembled each other quite as closely as did the other mimicking species he has described; and since all these insects appear to be equally protected by their inedibility, and to be equally free from persecution, it was not easy to see why this curious resemblance existed, or how it had been brought about. That it is not due to close affinity is shown by the fact that the resemblance occurs most frequently between the two distinct sub-families into which (as Mr. Bates first pointed out) the Heliconidæ are naturally divided on account of very important structural differences. One of these sub-families (the true Heliconinæ) consists of two genera only, Heliconius and Eueides, the other (the Danaoid Heliconina) of no less than sixteen genera; and, in the instances of mimicry we are now discussing, one of the pairs or

1 Professor Meldola informs me that he has recorded another case of mimicry among British moths, in which Acidalia subsericata imitates Asthena candidata. See Ent. Mo. Mag., vol. iv. p. 163.

triplets that resemble each other is usually a species of the large and handsome genus Heliconius, the others being species of the genera Mechanitis, Melinæa, or Tithorea, though several species of other Danaoid genera also imitate each other. The following lists will give some idea of the number of these curious imitative forms, and of their presence in every part of the Neotropical area. The bracketed species are those that resemble each other so closely that the difference is not perceptible when they are on the wing.

In the Lower Amazon region are found