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Darwin Correspondence Project

From H. W. Bates   18 February 1868

Royal Geographical Society | 15, Whitehall Place, S.W.

Feby 18 1868

My dear Mr Darwin

I could not myself remember any case of female insects being very conspicuously more numerous than the males & therefore put the question, as you desired to the Entomological Society, last night. Some facts & good opinions were elicited:—1

Mr Stainton said that observations of numerical proportion of the sexes, in collecting were quite unreliable, for it was a well-known fact that in collecting Tineina moths the females were nearly in all species very scarce, whereas in breeding the females proved to be more numerous—as 2 to 1 to the males.2 Mr F. Smith also stated that observations in the field were of little value. He quoted some most interesting experiments he was making in breeding some British Sawflies—all the individuals turning out to be females.3 These I think will prove to be cases of parthenogenesis: Mr Smith will write to you himself.

Other members gave these cases:—

Tomicus villosus (bark Coleopter of the oak)4

no male found by Ratzeburg during many years observation5

Tomicus dispar— an English species

males exceedingly rare6

Miana arcuosa7— an English moth—

males fly in great

numbers over damp meadows in many places—females only

one or two in a season

Apatania muliebris8  

an English Neuropterous insect  

hundreds of females found

during last two years— no male yet found

In Hemerobiidæ according to Maclachlan females are much more numerously found than the males.9

One of the above cases I have mentioned by mistake—it being the reverse illustration—males more numerous than females.— Plenty of cases can be mentioned of males occurring more numerous; but after the strongly expressed opinions of Stainton & Smith & the case of the Tineina (which was confirmed by other able observers, Mr F. Bond among them)10 I must say I shall hereafter hesitate to accept any fact, without reserve, of sexual disparity in numbers without the species are actually bred. Although the cases of vast majority of ♂ butterflies in hot countries seem pretty clear, yet it is possible the females may, in some unaccountable manner, elude observation.

Perhaps in selecting species for figuring in your next work, it would be better to chose the most wonderful, altho’ they may not be British. The Chilian stag beetle Chiasognathus, would surprise people more than our common insect.11 I am now reading your two Volumes. Pangenesis I have read once & must read again before I thoroughly understand it.12 A friend tells me the same.

Yours sincerely | H W Bates

CD annotations

1.1 I could … value. 2.5] crossed pencil
2.2 in collecting … the males. 2.4] scored red crayon
2.4 He quoted … rare 3.4] crossed ink
3.5 Miana … season 3.6] crossed pencil, double scored red crayon; ‘x male [more] numerous’ added red crayon
3.9 In … the males. 3.10] double scored red crayon
4.1 One of … observation 4.8] crossed pencil
4.2 Plenty of … numerous; 4.3] double scored red crayon
4.7 Although … observation. 4.8] scored red crayon
5.1 Perhaps … same. 5.5] heavily crossed pencil
Top of letter: ‘Sexes’ red crayon; ‘state that [two words illeg] question before Soc’ pencil


CD requested information on the proportion of the sexes in insects in his letter to Bates of 11 February [1868]. Bates had put the question to the meeting of the Entomological Society of London on 17 February 1868. The ensuing discussion was reported in the society’s Transactions for 1868, pp. x–xi, and is summarised in Descent 1: 310.
Henry Tibbats Stainton had published extensively on the Tineina moths (ODNB). Tineina was a taxon defined by Stainton as comprising fifteen families of Lepidoptera including the smallest known moths (see Stainton 1867, pp. 59–60, 84–8). The name Tineina is not used in modern taxonomy. CD cited Stainton on the proportion of the sexes in the smaller moths in Descent 1: 310.
The results of Frederick Smith’s breeding experiments with sawflies (Tenthredinidae) are reported in Descent 1: 314.
CD reported the remarks of Edward Westey Janson on the preponderance of females in the bark-eating beetle Tomicus villosus (now Dryocoetes villosus) in Descent 1: 314.
Julius Theodor Christian Ratzeburg was an expert on forest insects.
Tomicus dispar is now Xyleborus dispar.
Miana arcuosa is now Photedes minima (small dotted buff).
Apatania muliebris is now in the order Trichoptera (caddisflies).
The family Hemerobiidae (brown lacewings) is in the order Neuroptera. Bates refers to Robert MacLachlan.
Bates refers to Chiasognathus grantii. See letter to H. W. Bates, 11 February [1868] and n. 8.
The reference is to the chapter ‘Provisional hypothesis of pangenesis’ in Variation 2: 357–404.


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

ODNB: Oxford dictionary of national biography: from the earliest times to the year 2000. (Revised edition.) Edited by H. C. G. Matthew and Brian Harrison. 60 vols. and index. Oxford: Oxford University Press. 2004.

Stainton, Henry Tibbats. 1867. The Tineina of Syria and Asia Minor. London: J. van Voorst.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Has put question of proportion of sexes in insects to the Entomological Society. Quotes H. T. Stainton and F. Smith. Cites some cases mentioned by other members.

Is reading Variation; does not quite understand Pangenesis.

Letter details

Letter no.
Henry Walter Bates
Charles Robert Darwin
Sent from
R Geogr. Soc.
Source of text
DAR 86: A4–5
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5893,” accessed on 28 May 2024,

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