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Darwin Correspondence Project

From E. W. Janson   4 June 1868

30, Museum Street, | London, | W.C.

4th June 1868

Chas Darwin, Esq. M.A., F.R.S., etc

Down, | Bromley, Kent, | SE.

Dear Sir,

Referring to my respects of the 30th. ultimo, I beg to advise that I forward to your address as above by this post a small box containing the insects specified in the enclosed Invoice.1

I find that although Lacordaire makes no mention of stridulating organs in Trox, Erichson (Naturgeschichte der Insecten Deutschlands, III. 927) alludes to them thus:

“Die Käfer lassen einen zirpenden Laut hervor, welcher durch Reiben des Hinterleibs gegen die Flügeldecken hervorgebracht wird. Die auf der Innenseite sehr glatten Flügeldecken haben längs des Aussenrandes eine Reihe erhabener Puncte, über welche die runzlig-punctirten, umgeschlagenen Seiten des Hinterleibes streichen.”2

I send the only example I can find amongst the Oryctidae in which stridulating organs co-exist with external sexual distinctions.3

Trusting that insects now sent may all prove useful, and ever at your service. | I am, | Dear Sir, | Yours very truly & respectfully, | Edward W. Janson


30, Museum Street, | London, | W.C.

4th June 1868

C. Darwin, Esq

To E. W. Janson, Natural History & General Agent, and Bookseller.
2 Trox sabulosus, L.—Europe @ 3d. 6d
1 Do bullatus,4 Curtis.— Chili 6.
Oryctes Senegalensis, Burm.—5 Senegal ⚥ 1.
Box 6
—. 2. 6

CD annotations

1.1 Referring … Invoice. 1.3] crossed pencil
4.1 I send … service. 5.1] crossed pencil
Top of letter: ‘Trox’ pencil
End of letter: ‘(oryctes & Trox)’ pencil, partly erased
Verso of enclosure:
‘Necrophorus a [del ‘foreign’] pair if sexes can be distinguished
Cerambycidæ do
any Dynatidæ pair
Onitis (a male alone)’6


Janson’s letter to CD of 30 May 1868 has not been found; nor has any letter from CD requesting more insects in addition to those that Janson sent with his letter of 25 May 1868. See, however, the letter to H. W. Bates, 21 May [1868].
Jean Théodore Lacordaire discussed Trox in Lacordaire 1854–75, 3: 150–1. The quotation is from Wilhelm Ferdinand Erichson in Erichson 1848, and may be translated: The beetles make a stridulous noise caused by the rubbing of the abdomen against the elytra. The elytra, which are very smooth on the inside, have along their outer edges a row of raised points, over which the stippled sides of the abdomen rub. Erichson wrote ‘hören’, not ‘hervor’.
CD discussed sexual differences in the stridulating organs of some species of Oryctes, including Oryctes senegalensis, in Descent 1: 383–4. Oryctes senegalensis is now O. boas (Coloeptorum catalogus vol. 21, part 156, p. 68).
That is, Trox bullatus.
See n. 3, above.
No correspondence between CD and Janson concerning these specimens has been found. See also letter from E. W. Janson, 25 May 1868 and n. 11. Bates mentioned the Dynastidae as ‘remarkable for stridulating organs’ in his letter of 28 May 1868.


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

Erichson, Wilhelm Ferdinand. 1848. Coleoptera, vol. 3, part 1. Part of Naturgeschichte der Insecten Deutschlands. Berlin: Nicolaischen Buchhandlung.

Lacordaire, Jean Théodore. 1854–75. Histoire naturelle des insectes. Genera des Coléoptères, ou exposé méthodique et critique de tous les genres proposés jusqu’ici dans cet ordre d’insectes. 11 vols. in 12. Paris: Librairie encyclopédique de Roret.


Sends specimens of Coleoptera.

Quotes from W. F. Erichson [Naturgeschichte der Insecten Deutschlands 3: 927] on stridulating organs in Trox.

Letter details

Letter no.
Edward Westey Janson
Charles Robert Darwin
Sent from
London, Museum St, 30
Source of text
DAR 82: A101–2
Physical description
1p † enc

Please cite as

Darwin Correspondence Project, “Letter no. 6228,” accessed on 21 October 2021,

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