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Darwin Correspondence Project

From A. R. Wallace   10 March 1869

9, St. Mark’s Crescent | NW.

March 10th. 1869

Dear Darwin

Thanks for your kind note. I could not persuade Mr. Macmillan to cut more than 25 copies for my own friends, & he even seemed to think this a sign of most strange and barbarous taste.1

Mr. Weir’s paper on the kinds of larvæ &c. eaten or rejected by insectivorous birds, was read at the last meeting of the Entomological Society & was most interesting & satisfactory.2 His observations & experiments, so far as they have yet gone, confirm in every instance my hypothetical explanation of the colours of catterpillars. He finds that all nocturnal feeding obscure coloured catterpillars, all green & brown and mimicking catterpillars, are greedily eaten by almost every insectivorous bird. On the other hand every gaily coloured spotted or banded species, which never conceal themselves, & all spiny & hairy kinds are invariably rejected, either without or after trial.3

He has also come to the curious & rather unexpected conclusion, that hairy & spiny catterpillars are not protected by their hairs,—but by their nauseous taste, the hairs being merely an external mark of their uneatableness, like the gay colours of others— He deduces this from two kinds of facts—1st. That very young catterpillars before the hairs are developed are equally rejected,—and 2nd—that in many cases the smooth pupæ & even the perfect insect of the same species, are equally rejected.

His facts it is true are at present not very numerous, but they all point one way. They seem to me to lend an immense support to my view of the great importance of protection in determining colour,—for it has not only prevented the eatable species from ever acquiring bright colour spots or markings injurious to them, but it has also conferred on all the nauseous species distinguishing marks to render their uneatableness more protective to them than it would otherwise be.

When you have read my book I shall be glad of any hints for corrections if it comes to another edition— I was horrified myself by coming accidentally on several verbal inelegancies after all my trouble in correcting, & I have no doubt there are many more important errors.

Believe me Dear Darwin | Yours very truly | Alfred R. Wallace

CD annotations

End of letter: ‘Sondaicus | Volcanic outburst’4 pencil


See letter to A. R. Wallace, 5 March [1869] and n. 2. Wallace refers to his publisher, Alexander Macmillan, and to Wallace 1869a.
John Jenner Weir’s paper ‘On insects and insectivorous birds’ (Weir 1869) was read on 1 March 1869. CD cited it in Descent 1: 417.
Wallace had been asked by CD to suggest a solution to the problem of bright colours in caterpillars as well as butterflies. CD had maintained that bright colours in butterflies were due to sexual selection (see Correspondence vol. 15, letter to A. R. Wallace, 23 February 1867). Wallace suggested that Weir might conduct experiments in his aviary to test Wallace’s hypothesis that bright colours served as protection (see Correspondence vol. 15, letter from A. R. Wallace, 24 February [1867]). CD and Wallace continued to discuss the problem in 1868 (see Correspondence vol. 16).
CD’s annotations are notes for his reply to Wallace. See letter to A. R. Wallace, 22 March [1869].


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 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.

Weir, John Jenner. 1869. On insects and insectivorous birds; and especially on the relation between the colour and the edibility of Lepidoptera and their larvae. [Read 1 March 1869.] Transactions of the Entomological Society of London (1869): 21–6.


Weir’s paper on relation of protection to colour of caterpillars [Trans. R. Entomol. Soc. Lond. (1869): 21–6; (1870): 337–9] confirms ARW’s hypothesis.

Letter details

Letter no.
Alfred Russel Wallace
Charles Robert Darwin
Sent from
London, St Mark’s Crescent, 9
Source of text
DAR 106: B77–8
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 6651,” accessed on 14 April 2024,

Also published in The Correspondence of Charles Darwin, vol. 17