My dear M^r. Darwin,

My brother is greatly obliged for your kindness in subscribing for a copy of his forthcoming Flora.¹ He hopes to get the book out towards the end of this year.

As regards the relative numbers of the sexes in various species of Butterflies, the following cases of males in excess are noted in my work on S. African Rhopalocera.²

Eronia Buquetii (Pieridæ).³

Of this, though abundant at Plettenberg Bay,⁴ I never took a single ♀.— Rhop. Afr. Austr. I, p. 66.

Danais Echeria (Danaidæ).⁵

The ♀ of this must be much scarcer than the ♂, as amongst a large number of examples, taken at random during my 9 months’ residence at Knysna⁶ there was but one of the former sex.— R. A. A. I, p. 87.

Leptoneura Clytus (Satyridæ.)

There can be no question about the preponderance of ♂s in this species, which swarms in open ground at the Cape from February to May. I have estimated the proportion of ♂s to ♀s to be as 50 to 1.—⁷ R. A. A. II, p. 194.

Zeritis Alphæus (Lycænidæ).

During seven years’ acquaintance with this butterfly, I only met with 5 ♀s, though the ♂s are numerous in certain localities.—⁸ R. A. A. II, p. 271.

Other instances, not mentioned in my work, but almost as remarkable, are those of Papilio Merope, Debis dendrophilus, and Erebia Sabacus.⁹ In the following cases, ♂s are decidedly more numerous, though the disproportion in numbers is not nearly so great. Papilio Nireus, Anthocharis Ione and Evarne, Acræa Violarum, Nohara, and Petræa, Atella Phalanta, Diadema Bolina, Erebia Hyperbius, Zeritis Chrysaor & Thysbe, and Pamphila Mohopaani.¹⁰

Cases of females in excess are certainly rare amongst butterflies. Only three instances occur to me among S. African species, and it is not impossible that further observation will show these to be more apparent than real. The three species are Iolaus Silas and Zeritis Pyroeis among the Lycænidæ, and Pyrgus Mohozutza among the Hesperiidæ¹¹

Bates brought the subject forward at the last Meeting of the Entomological Socy, and the discussion was rather interesting.¹² Several Members seemed to think that little reliance could be placed on the observation of species in nature, and that if insects were bred in large numbers from the larvæ, the numbers of the sexes would be found about equal. Making all allowance for the retiring habits of the ♀, however, I am convinced that the aspect of affairs in nature is not on the whole misleading; or why should we find so many cases where ♀s are as common as ♂s? and a few in which they appear to be even commoner?

The common Lasiocampa Quercus of this country occurs to me as a good instance of large excess of ♂s. The ♂s of this Bombyx, as is well known, spend all their life (they take no food in the imago state), as moths, in an impetuous search for the ♀. The number of ♂s that assemble about a single ♀ seems to show how scarce are individuals of the latter sex, or why should the competition be so keen? If you rear a ♀ from the pupa, & take her out of doors (though only in a box in your pocket) you are soon surrounded by ♂s in a high state of excitement. One autumn, in the Isle of Wight, I tried this experiment; and was surprised to find, on one occasion, that even the box where the virgin ♀ had been on the previous day was still attractive, as many as five ♂s strenuously endeavouring to gain admittance!¹³

I shall not fail to communicate to you any facts that seem to me to bear upon this interesting question. But, as Bates observed the other night, so little attention has been paid to these particulars, that a “new set” of careful observations must be made before any good can be done.

Always sincerely yours, | Roland Trimen.