Tirumala hamata

Robinson, Jeanne & Vane-Wright, Richard I., 2018, A specimen of Tirumala hamata hamata (Macleay, 1826) (Lepidoptera: Danainae) from Captain Cook’s first voyage, Journal of Natural History 52 (11 - 12), pp. 687-712 : 697-698

Why was Tirumala hamata initially misidentified?

To be fair to Banks, in his diary he stated only that the Thirsty Sound butterfly was ‘much like’ Linnaeus’ s Papilio similis . This, however, was evidently accepted by Fabricius as a correct identification. How did this confusion with a butterfly from China, now considered so distinct as to be placed in a separate genus, come about? The most obvious answer is mimicry, as with Danaus plexippus and Limenitis archippus , Danaus chrysippus and Hypolimnas misippus , and various other butterflies which, up to the mid-nineteenth century, caused similar confusion ( Vane-Wright 2007a). Linnaeus, Banks, Fabricius and many other outstanding eighteenth-century naturalists were working within a special creation framework (even though Fabricius and even Linnaeus himself started to have doubts; Vane-Wright 2007b). It wasn’ t until the theory of evolution by natural selection was announced to the world by Charles Darwin and Alfred Wallace in 1858, and then Henry Bates introduced his mimicry hypothesis in 1862, that there was any reason to think, let alone expect, that well-defended organisms in the same environment would come to look deceptively similar due to signal-pattern convergence.

Indeed, the idea of ‘convergence’ itself makes no sense until you have a general theory of divergent evolution. Although the publications of Lamarck and others introduced such a general theory in the early nineteenth century, evolution was not widely embraced until after the publication of Darwin’ s Origin, in 1859. In the case of the milkweed butterflies discussed here, by the time that Fabricius was organising Hunter’ s collection, up to eight ‘blue tiger’ patterned species had been named (Appendix 3: Table 3), but all were widely confused in both collections and the literature; even today, misidentifications are common on the Internet.

Although Ideopsis similis and Tirumala hamata collectively cover almost all of the Indo-Pacific tropics and subtropics, their geographical ranges do not overlap. However, subsets of the Indo-Australian blue-tiger-patterned milkweed butterflies overlap in many areas ( Morishita 1981; Ackery and Vane-Wright 1984). For example, T. liminace , so often confused with both Ideopsis similis and T. hamata , occurs with the former in continental South-east Asia, and with the latter in the Philippines, Java and western Lesser Sunda Islands. Thus, mimicry in a broad sense can offer an explanation for the eighteenth-century confusion of Ideopsis similis and Tirumala hamata . However, these observations suggest further possibilities, such as ancestral patterns, non-divergence and symplesiomorphy, in addition to convergence and mimicry – issues which one of us (RIVW) proposes to explore elsewhere.