To Henry Doubleday   20 March [1868]¹

My dear Sir

You have been so very kind in offering to aid me that I apply once again.—² I was told at B. Mus. that you had made observations on Anobium tesselatum & had sent living specimens there. I was told that you had stated (& M^r F. Smith in consequence observed the same fact) that the ticking sound is a sexual call.³ Is it made first or principally by the male, & answered by the female? The answering by the female seems to make the case different from the music of the Orthoptera & Homoptera.⁴

I am interested by this case, as it is the first of which I have heard of noises emitted by Coleoptera for sexual purposes. Is the noise made by the thorax or head hitting against the wood?

I think that I mentioned to you that I inferred from a letter from D^r. Wallace of Colchester,—that he supposed that the statements by M^r Stainton & others that they bred more females than males from caterpillars, might be accounted for by these collectors collecting the largest & finest caterpillars. But this was an error on my part, & D^r. W. maintains that collectors collect equally large & small caterpillars;⁵ so that I am all astray again, & can in no way conceive why these gentlemen sh^d have had such different results when collecting free insects & breeding them.

Do you agree with D^r. Wallace that collectors w^d collect indifferently large & small caterpillars?—

My dear Sir | Yours sincerely obliged | Ch. Darwin