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Darwin Correspondence Project

To Alfred Russel Wallace   23 February 1867

Down, Bromley, Kent, S.E.

February 23, 1867.

Dear Wallace,—

I much regretted that I was unable to call on you, but after Monday I was unable even to leave the house.1 On Monday evening I called on Bates2 and put a difficulty before him, which he could not answer, and, as on some former similar occasion, his first suggestion was, “You had better ask Wallace.” My difficulty is, why are caterpillars sometimes so beautifully and artistically coloured? Seeing that many are coloured to escape danger, I can hardly attribute their bright colour in other cases to mere physical conditions. Bates says the most gaudy caterpillar he ever saw in Amazonia (of a Sphinx) was conspicuous at the distance of yards from its black and red colouring whilst feeding on large green leaves.3 If anyone objected to male butterflies having been made beautiful by sexual selection, and asked why should they not have been made beautiful as well as their caterpillars, what would you answer? I could not answer, but should maintain my ground.4 Will you think over this, and some time, either by letter or when we meet, tell me what you think? Also, I want to know whether your female mimetic butterfly is more beautiful and brighter than the male?5

When next in London I must get you to show me your Kingfishers.6

My health is a dreadful evil; I failed in half my engagements during this last visit to London.—7 Believe me, yours very sincerely, | C. Darwin.


CD had been at 6 Queen Anne Street in London, the home of his brother, Erasmus Alvey Darwin, from 13 to 21 February (see ‘Journal’, Appendix II).
Henry Walter Bates.
In a note dated 18 February 1867, CD wrote that Bates had observed a caterpillar of the sphinx moth (family Sphingidae). CD had been considering this general question as early as 1861 (see DAR 81: 5). CD discussed colourful caterpillars and gave more detail of Bates’s observation in Descent 1: 415–16. Wallace and Bates had travelled together in the Amazon River basin (DNB).
For CD’s interest in sexual selection, see the letter to Fritz Müller, 22 February [1867] and n. 8. See also letter from Alfred Newton, 21 January 1867 and n. 8. The first extant letter from CD to Wallace concerning CD’s belief in the importance of sexual selection is the letter to A. R. Wallace, 28 [May 1864] (Correspondence vol. 12).
In his letter of 19 November 1866 (Correspondence vol. 14), Wallace told CD that he had a metallic-blue female Diadema that mimicked a metallic-blue Euploea; he also wrote that the male Diadema was dusky brown. In his paper ‘On reversed sexual characters in a butterfly’ (A. R. Wallace 1866a, p. 186), Wallace suggested the name Diadema anomala (now Hypolimnas anomala, the Malayan eggfly); he pointed out that it was the female of the species that mimicked the male Euploea midamus (blue-spotted crow). CD mentioned the case in Descent 1: 413. CD also discussed mimetic butterflies with Wallace when he was in London later in November 1866 (see letter to Alfred Newton, 19 January [1867]).
CD and Wallace evidently had a discussion on the differences between the sexes in kingfishers when CD was in London in November 1866 (see letter to A. R. Wallace, 29 April [1867] and n. 6). In 1862, Wallace had returned from eight years in the Malay Archipelago and had since organised his extensive collections (see Correspondence vol. 12, letter from A. R. Wallace, 2 January 1864, and A. R. Wallace 1905, 1: 385–405). Wallace’s kingfishers were displayed in his Bayswater exhibition (see letter from A. R. Wallace, [19 June 1867] and n. 3, and A. R. Wallace 1905, 1: 404).


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

DNB: Dictionary of national biography. Edited by Leslie Stephen and Sidney Lee. 63 vols. and 2 supplements (6 vols.). London: Smith, Elder & Co. 1885–1912. Dictionary of national biography 1912–90. Edited by H. W. C. Davis et al. 9 vols. London: Oxford University Press. 1927–96.

Wallace, Alfred Russel. 1905. My life: a record of events and opinions. 2 vols. London: Chapman & Hall.


Asks why caterpillars are sometimes beautifully coloured. It poses a problem for view that sexual selection is the explanation of colours of male butterflies.

More on mimetic butterflies.

Letter details

Letter no.
Charles Robert Darwin
Alfred Russel Wallace
Sent from
Source of text
Marchant ed. 1916, 1: 178

Please cite as

Darwin Correspondence Project, “Letter no. 5415,” accessed on 23 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 15