Page:Darwinism by Alfred Wallace 1889.djvu/268



In tropical Asia, and eastward to the Pacific Islands, the Danaidæ take the place of the Heliconidæ 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 Euplæa 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.

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 Liparidæ (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