Dear Sir

As I am now laid up with spasmodic asthma & may not see you again before you leave London; I write to mention one or two facts which I had not time to tell you the other day.¹

Although the ocelli on butterflies do not differ very considerably in the sexes & where they do differ the females have the extra or the larger ocelli;² this need not militate against the existence of sexual selection in insects; there is not a question that insects have the power of repelling one another & that they use this power, and considering the marvellous differences between the sexes of many species, there is no reason to suppose that the power of repelling is not used by the females in selecting partners:

Last year I was on the look out for instances of rejected proposals amongst insects; whilst waiting 20 minutes for a late train one morning, I watched a pair of the small common white butterfly, the female was evidently tired & the male flew round her attempting to induce her to become his wife, she evaded him for a quarter of an hour when, utterly worn out, she dropped on to the platform & closed her wings; the male came down, walked round her, touched her with his antennæ & tried all he could to arouse her, but in vain, he at length flew away in disgust, and just as my train came up I saw the female flagging off to the railway bank.³

I took a pair of Bibio, the large black species, (I forget the specific name) in copula;⁴ but whilst putting them into a small glazed pocket box they separated; I then threw away the male & put a fresh male in with the disconsolate wife, she seemed much annoyed & every time he approached her whilst walking round the box, she kicked out her middle leg on one side & held him at leg’s length.

I noticed several other cases during the year but omitted to note the circumstances, but so far as I can remember the most approved plan amongst butterflies seems to be—to drop to the ground & close the wings, as in the case mentioned above.

By the bye do dogs blush? my wife says that a little black dog was out with her once on a boating excursion & the seasickness affected him so much that he became deadly pale. If so—why shouldn’t he blush or at anyrate flush at other times?

yours very sincerely | A G Butler

Ch. Darwin Esq FRS | &c &c &c.