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Darwin Correspondence Project

From Roland Trimen   20 February 1868

71, Guildford Street, | Russell Square, | London. W.C.

20th. February, 1868.

My dear Mr. 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.

CD annotations

1.1 My … year. 1.2] crossed blue crayon
6.1 Zeritis Alphæus] ‘4’ added pencil
7.2 Erebia Sabacus.] ‘3’ added and circled pencil
7.5 Pamphila Mohopaani 7.6] ‘12’ added pencil
10.2 The ♂s … keen? 10.5] scored blue crayon
10.4 The number … keen? 10.5] ‘Lasiocampa Quercus’ added ink
Top of letter: ‘Letter 2. | Will the same male serve several females | Trimen’ blue crayon; ‘Keep | organ of smell’ red crayon


See letter to Roland Trimen, 12 February [1868] and n. 2. The reference is to Flora of Middlesex by Henry Trimen and William Turner Thiselton-Dyer (H. Trimen and Thiselton-Dyer 1869).
R. Trimen 1862–6. Rhopalocera is a former suborder in the taxonomy of Lepidoptera, based on the club-shaped structure of the antennae, and comprising the butterflies and skippers (see R. Trimen 1862–6, p. 6).
Eronia buquetii is now Nepheronia buquetii (Buquet’s vagrant).
Plettenberg Bay is in the Cape of Good Hope (now Western Cape province, South Africa), about 100 miles west of Port Elizabeth.
Danais echeria is now Amauris echeria (family Nymphalidae).
Knysna is in the Cape of Good Hope (now Western Cape Province, South Africa), about 150 miles west of Port Elizabeth.
Leptoneura clytus is now Dira clytus (subfamily Satyrinae, family Nymphalidae). CD mentioned a case in which males outnumbered females fifty to one in Descent 1: 310, but did not name the species.
Zeritus alphaeus is now Capys alphaeus (the protea scarlet). CD mentioned this case in Descent 1: 310, but did not name the species.
Papilio merope (now Heteronympha merope), Debis dendrophilus (now Paralethe dendrophilus), and Erebia sabacus (now Pseudonympha magus) are in the subfamily Satyrinae.
Papilio nireus is in the family Papilionidae. Anthocharis ione (now Colotis ione, the purple tip), and Anthocharis evarne (now Colotis eucharis, the plain orange tip) are in the family Pieridae. Acraea violarum, A. nohara, A. petraea (the blood acraea), Atella phalanta (now Phalanta phalantha, the common leopard), and Erebia hyperbius (now Argyreus hyperbius, the Indian fritillary) are in the subfamily Heliconiinae; Diadema bolina (now Hypolimnas bolina, the common eggfly) is in the subfamily Nymphalinae. Zeritis chrysaor (now Poecilmitis chrysaor, the golden copper), and Z. thysbe (now Poecilmitis thysbe, the opal copper) are in the family Lycaenidae; Pamphila mohopaani (now Pelopidas thrax inconspicua, the millet skipper) is in the family Hesperiidae. In Descent 1: 310, CD noted that Trimen had found the number of males in excess in nineteen species from South Africa.
Zeritis pyroeis is now Poecilmitis pyroeis. Pyrgus mohozutza is now Kedestes mohozutza, the fulvous ranger. CD cited Trimen’s view that, with the exception of three South African species, females are rarely preponderant in butterflies in Descent 1: 310.
CD reported Trimen’s experiment with Lasiocampa quercus (in the family Lasiocampidae, superfamily Bombycoidea) in Descent 1: 312.


Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

Trimen, Roland. 1862–6. Rhopalocera Africæ Australis; a catalogue of South African butterflies, comprising descriptions of all the known species with notices of their larvæ, pupæ, localities, habits, seasons of appearance, and geographical distribution. London: Trübner. Cape Town, South Africa: W. F. Mathew.


Proportion of sexes in butterflies; discussion of subject at meeting of Entomological Society, London.

Attraction of males by female Lasiocampa quercus. [see Descent 1: 311–12.]

Letter details

Letter no.
Roland Trimen
Charles Robert Darwin
Sent from
London, Guildford St, 71
Source of text
DAR 85: B59–60a
Physical description
5pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5902,” accessed on 12 April 2021,

Also published in The Correspondence of Charles Darwin, vol. 16