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Darwin Correspondence Project

From John Blackwall   18 February 1868

Hendre House,

February 18th, 1868.

Dear Sir,

I am pleased to learn that any of the particulars contained in my last letter interested you, and I assure you that I shall be glad at all times to communicate such facts in the natural history of the Araneidea as have come to my knowledge.1

As Atypus Sulzeri, Theridion tinctum and Epeïra conica do not occur in this locality,2 I am incompetent to form an opinion with regard to the probable numerical proportion of the sexes of those species respectively. The sexes of Thomisus bifasciatus do not seem to present any marked difference as to numbers;3 the males undoubtedly are most frequently seen, but this circumstance may be ascribed with much probability to their being more erratic than the females, and this remark is applicable to numerous species.4 The females of Thomisus floricolens and Tho. citreus appear to be more abundant than the males, which differ from their mates remarkably both in size and colour.5 The males of Sparassus smaragdulus and Epeïra bicornis differ conspicuously from the females in colour;6 they are smaller also than the latter sex, and of less frequent occurrence.

Decided differences may be observed in the colours and in the designs formed by their distribution in the sexes of the following species; Philodromus dispar, Theridion Carolinum and Linyphia fuliginea;7 the males are smaller also and appear to be fewer in number than the females. The figure of the male Philodromus dispar given in the “History of British Spiders” was made from a specimen whose colours had been affected by the spirit in which it was preserved (see the description of this species, pt. 1, pp. 91, 92).8

The males of species comprised in Dr. Leach’s genus Nephila (a division of the family Epeïridæ)9 apparently bear a very small proportion both in number and size to the females, from which they differ also remarkably in colour. These facts are strikingly illustrated in the “Aranéides des Iles de la Réunion, Maurice et Madagascar,” by Auguste Vinson, pl. V, figs. 1 & 2; and pl. VI, figs. 1 & 2.10 M. Vinson appears to be the only person who has captured the male of Scytodes thoracica, a species widely distributed and far from being uncommon.11 As a rule, I think that male spiders differ more decidedly than females from the ordinary colouration of the genera to which they belong.12

Let me caution you not to attach too much importance to the statements of an individual who has resided for thirty-five years in a secluded valley, where there are neither public libraries, museums, nor students of any department of zoology, and who, consequently, has to depend mainly on his own resources.

I am, dear Sir, | very truly yours | John Blackwall.

CD annotations

1.1 I am … respectively. 2.3] crossed pencil
2.3 sexes of Thomisus bifasciatus 2.4] underl red crayon
2.5 this circumstance … species. 2.7] scored red crayon
2.9 Sparassus smaragdulus] underl red crayon
2.9 Epeïra] underl red crayon
2.11 less] underl red crayon
3.2 Philodromus … fuliginea; 3.3] double scored red crayon
3.2 Philodromus] underl red crayon
3.2 Theridion 3.3] underl red crayon
3.3 Linyphia] underl red crayon
3.3 the males … females. 3.4] double scored red crayon
4.1 The males … the females, 4.3] scored red crayon
4.1 Nephila] underl red crayon
4.7 As a rule, … belong. 4.9] double scored red crayon
Top of letter: ‘As males more erratic & conspicuous one wd be apt to overestimate them.’ ink; ‘Sexes | I doubt whether I have [asked this enough]red crayon
End of letter: ‘(I must admit a very great difficulty.)’ square brackets in original MS, ink; ‘equal [when young] | SizeTheridion—’ pencil


See letter from John Blackwall, 12 February 1868. CD’s reply to Blackwall has not been found. In nineteenth-century taxonomy, Araneidea was the order of ‘true spiders’; it is equivalent to the modern order Araneae.
Atypus sulzeri is now Atypus piceus (family Atypidae, purseweb spiders); Theridion tinctum is now Keijia tincta (family Theridiidae, cobweb weavers); Epeira conica is now Cyclosa conica (family Araneidae, orb weavers).
Thomisus bifasciatus is now Xysticus bifasciatus (family Thomisidae, crab spiders).
In Descent 1: 314–15, CD noted that according to Blackwell, male spiders ‘from their more erratic habits’ were more commonly seen, and therefore appeared to be more numerous.
Thomisus floricolens is now Diaea dorsata (family Thomisidae); T. citreus is now Misumena vatia (family Thomisidae). CD mentioned the differences in colour between males and females of these two species in Descent 1: 337.
Sparassus smaragdulus is now Micrommata virescens (family Sparassidae, giant crab spiders); Epeira bicornis is now Gibbaranea gibbosa (family Araneidae). See Descent 1: 337.
Theridion carolinum is now Neottiura bimaculata (family Theridiidae); Linyphia fuliginea is now Microlinyphia pusilla (family Linyphiidae, dwarf and sheetweb weavers). See Descent 1: 337.
The reference is to Blackwall 1861–4. CD cited this work in Descent 1: 337.
William Elford Leach described Nephila (now in the family Tetragnathidae, long-jawed orb weavers) in Leach 1814–17, 2: 133–4. See Descent 1: 337.
Blackwall refers to Vinson 1863; plate V shows male and female Epeira inaurata (now Nephila inaurata, family Nephilidae, nephilid spiders), plate VI shows male and female E. nigra (now recognised as a colour variant of N. inaurata). CD cited the illustration of E. nigra from Vinson 1863 in Descent 1: 338 n. 14.
The male Scytodes thoracica (family Scytodidae, spitting spiders) is described in Vinson 1863, pp. 6–8, and plate I.
CD cited Blackwall on this point in Descent 1: 337–8.


Proportion of sexes in spiders; coloration.

Letter details

Letter no.
John Blackwall
Charles Robert Darwin
Sent from
Hendre House
Source of text
DAR 86: A2–3
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5892,” accessed on 20 June 2019,

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