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Darwin Correspondence Project

From Charles Spence Bate   11 February 1868

8, Mulgrave Place, | Plymouth.

Feby 11. 68

My dear Sir


I am delighted to have a letter from you again & to see a part of it in your own hand writing:1

In regard to color in Crustaceæ my personal experience is limitted to British specimens.2 I know of none in which variation of color is dependent upon sex. Specimens vary sometimes but I have attributed the variation to other causes: Deep water specimens are generally redder than those which live near the shore: I have thought this to be dependent upon the less amount of light in deep water. Oceanic species that live near the surface of the water very frequently are of a deep Indigo blue: There is a species of Idotea that differs little or nothing from one of our littoral species except in being of an uniform deep Blue—where as the shore species differs from reddish brown to light green according to the colour of the weed on which it lives (feeding)— Brachyscelus lives on medusæ I believe & a great number of specimens should be examined before it could be determined that the variation in color is not due to other causes than that of sex.3

Gelasimus lives generally in holes on the sea shore. It is probably the case that the male is the more active and erratic of the two,4 thus light might influence the color of the more exposed sex:

I received recently a curious little species of crab from Borneo, that lives in a sponge: I could always tell the males from the females by the amount of epidermis rubbed off the dorsal surface of the females, being much more than from the males: The Females nestled closer & more constantly in the sponge than the males, which were necessarily more erratic & consequently less rubbed.5

You will thus perceive that I believe that whenever color varies in the sexes it is due to a change of habit only & would be the same in the female if the two were under like circumstances

I have however two rather large collections that I am now looking over, in which the collectors have attended much & noted the colors of the animals when alive & if I find any reason to modify this expression of my opinion I will write to you

Structure of Male

I do not know that the males fight for the females at least to any great extent: I remember once putting in two males of Carcinus mænas—our common shore crab—into a pan with a female. The female before having been put into the pan had been in the possession of a small male. But when I looked again she was in possession of the larger—that is the stronger animal— If they fought for possession the victory was a Bloodless one for I saw no wounds or injury.

Once I remember separating a male & female Gammarus from each other. they were in a pan with a great many others   The female swam immediately towards the mass of others that were congregated together   the male dashed fiercely round the pan two or three times & then in amongst the crowd of others & took the same female out from among the mass of others—but there was no fighting for possession of the female. it may have been as I think generally is the case with them that the females were the more numerous.6

The claws in this species are a trifle larger in the males than in the females but not more important that is sufficient to assist them in grasping the female well—one hand being thrust forward the other back thus hitched under the segments of the female.


The males have no other weapons for fighting than the females, except that in many the chelæ are developed larger— among our British species are the following genera in which the males have larger chelæ than the females7

Stenorhynchus Achaeus







Galathea andrewsii8










Exotic. are




There are others I dare say but I do not at present recollect them, but I believe that often species are made of the two sexes because of the different size limbs

Believe me My dear Sir | yours very sincerely | C Spence Bate.

CD annotations

1.1 I am … the shore: 2.4] crossed pencil
3.3 exposed] underl blue crayon; ‘(light)’ added above blue crayon; ‘& depth’ added above & del blue crayon
4.2 I could … than the males, 4.4] scored blue crayon
Structure of Male ] ‘2’ red crayon, circled red crayon
7.1 I do not … of the female. 8.6] crossed blue crayon
9.1 The claws … Caprella 11.17] crossed pencil
9.1 a trifle larger in the males] underl blue crayon
10.1 The males … larger— 10.2] scored blue crayon
10.1 in many the chelæ are developed larger— 10.2] underl & scored blue crayon
11.1 Stenorhynchus…Caprella 11.17] crossed pencil
11.1 Stenorhynchus … limbs 12.2] scored blue crayon
11.1 Stenorhynchus … andrewsii 11.8] ‘9 Genera British’ added ink
11.10 Orchestia … Caprella 11.17] ‘8 Genera British’ added ink
Top of letter: ‘Crustaceæ | 11’ blue crayon circled blue crayon


CD’s letter to Bate has not been found. He had corresponded with Bate while he was preparing his monographs on the Cirripedia (see Correspondence vol. 5).
Bate had published a number of works on British Crustacea, for example, Bate and Westwood 1863–8.
CD discussed sexual selection in the Crustacea in Descent 1: 328–37. Information from Bate on the coloration of Crustacea is given in Descent 1: 335. Idotea is a genus in the order Isopoda; Brachyscelus is a genus in the family Amphipoda.
Gelasimus is a synonym of Uca. CD asserted, partly on Bate’s authority, that male crustacea were more active and erratic than were females in Descent 1: 272.
This example is given in Descent 1: 335.
CD quoted from Bate’s letter on the absence of fighting between males in Carcinus maenas (the shore crab) in Descent 1: 332–4; he also reported Bate’s description of Gammarus marinus (now Chaetogammarus marinus) as showing that ‘in the Amphipoda, an order low in the scale’, the males and females recognised each other, and were ‘mutually attached’.
Bate’s information on the chelae of crustacea is given in Descent 1: 330–1.
Galathea andrewsii is now G. intermedia (Ingle and Christiansen 2004). The genera up to this point on the list are in the order Decapoda; the remainder on the list are Amphipoda.
Erichthoneus is not a valid genus; Bate considered it to be a synonym of Cerapus (see Bate 1862, p. 262).
See n. 4, above.
Bate mispelled Gecarcinus.


On the colours of sexes in Crustacea; the structure of male crabs.

Letter details

Letter no.
Charles Spence Bate
Charles Robert Darwin
Sent from
Source of text
DAR 82: A57–60
Physical description
8pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5864,” accessed on 15 February 2019,

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