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Darwin Correspondence Project

From A. F. Gray   8 May [1878]1

Dear Sir,—

The following case will, I think, prove of interest to you, as it corroborates your belief that freshwater shells are sometimes transplanted by the agency of aquatic birds.2

In the sketch I have endeavoured to give you a correct idea of the way in which the shell was attached to the duck’s foot.3

It was given to me by Mr. H. L. Newcomb, who shot the bird, which was a blue-winged teal (Querquedula discors), while flying, near the Artichoke river at West Newbury, Mass., September 6, 1877.4 The shell, the common mussel, or clam (Unio complanatus), is a very abundant species, being found in nearly all the rivers and ponds of the Atlantic slope.5 How long the shell had been attached is only a matter of conjecture, but it had abraded the skin of the bird’s toe, and left quite an impression. It was living when the bird was shot.

It would have undoubtedly been transplanted to some pond or river, perhaps miles from its original home, had the bird not been shot, and might then have propagated its kind.

Arthur H. Gray6

Danversport, Mass., May 8 | To C. Darwin, Esq.



The year is established by the date of publication of this letter in Nature. The letter was sent to Nature by CD (see letter to A. F. Gray, 21 May [1878]).
In Origin, p. 385, CD described an experiment in which he suspended a duck’s feet in an aquarium where freshwater shells were hatching and soon found numerous minute shells attached to the feet.
The original drawing has not been found but a woodcut was made of it for publication in Nature, 30 May 1878, p. 121; this image is reproduced here. See also letter to Nature, [21? May 1878]. The shell, together with the duck’s foot, is in the collection of the Museum of Comparative Zoology, Harvard (MCZ, Malacology 154590); see plate on p. 182.
H. L. Newcomb has not been identified. Querquedula discors is a synonym of Anas discors (blue-winged teal).
Unio complanatus is a synonym of Elliptio complanata (eastern elliptio), a freshwater mussel.
Gray’s middle initial was misprinted in Nature.


Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.


Found a live mussel attached to a blue-winged teal’s foot. Had the bird not been shot, the mussel might have been transported miles.

Letter details

Letter no.
Arthur Fairfield Gray
Charles Robert Darwin
Sent from
Danversport, Mass.
Source of text
Nature, 30 May 1878, p. 121

Please cite as

Darwin Correspondence Project, “Letter no. 11497,” accessed on 3 October 2023,