Dear Sir

I have been reading your Descent of Man & it has stirred me up to put together a few facts which I think may possibly prove useful to you—

The other day I was much interested in watching a male Anthocharis cardamines which as you know usually settles upon the wild carrot flowers: I was in a lane near a very attractive garden, no wild carrot grew within about half a mile of the spot, but at about 200 yards from the garden was a little patch of shepherds purse in flower & the orange-tip, every time he wished to settle left the garden & flew up the lane until he arrived at this patch where he alighted under my very nose & closed his wings, the shepherds purse concealed him almost as effectually as the wild-carrot; here I think was an amount of reasoning equal to that exhibited by Kallima when settling on its dead leaves—¹

Some years ago I wished to procure some fresh ♂ Pieris brassicæ² for my cabinet & I obtained them by means of a living female attached to a piece of thread so as to allow her to rise a short distance in the air.

Smith & Abbot, remarking on the resemblance borne by Callidryas Eubule to its foodplant, suggest that the female is led to deposit its eggs upon the plant which reminds it of its mate.³

You observe in ‘Sexual Selection’ that the sexes of the Hipparchiæ & Danaidæ do not differ, this is not strictly correct;⁴ Epinephele Janira differs so much in the sexes that Linnæus described it & its female as distinct, though consecutive, species; the male Danaids are (I think without exception) more likely to be rapid flyers than the females their frontwings being longer & more pointed.⁵

I have recently published a note in P.Z.S. on the frequent abnormalities in neuration of Acræa andromacha,⁶ I think we may see here how new genera take their rise amongst butterflies.

Whilst breeding Lepidoptera I have been struck with the much greater number of males in the commoner species & I think the excessive number of this sex is the cause of the ubiquity of such species   there can be no mistake about this in Orgyia antiqua, as the sex can be readily seen in the larval condition, the tufts of hair on the back being yellow in the ♂ & brown in the female.⁷

I can hardly think that the jaws of Lucanus cervus were developed solely (if at all) for the sake of fighting other males, as the females certainly hurt a great deal more than the males, as I know from personal experience, & I think we should find that the longer the jaws were the less powerful they would be; I think perhaps the variability in these jaws may be caused by a constant struggle between natural selection & sexual selection; the former demanding short jaws, the latter long.⁸

I don’t know if you have ever noticed the great difference in the sexes of the Crustacean genus Huenia (Decapods),⁹ I was much astonished when I suddenly dropped upon them today, the differences are about as under

Hoping that this long rigmarole will not worry you

Believe me to be | yours very sincerely | A G Butler.

Ch. Darwin Esq^re. | &c &c &c