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
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
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.
Please cite as
Darwin Correspondence Project, “Letter no. 5893,” accessed on 16 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-5893