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Darwin Correspondence Project

From Mary Treat   8 June 1874

Vineland, New Jersey,

June 8, 1874.

Dear Mr. Darwin,

Some time ago you asked me some questions with regard to Dionaea.1 I was not at that time prepared to answer, but since the latter part of April I have been giving the closest attention to these wonderful plants—now in their best working condition— I am with them during a large part of each day, while the insects are the most active. I have over thirty good, strong, vigorous plants; twenty-five of these I have numbered, and keep a record of the closing of each leaf, and the kind of insect it captures, and the number of days before it uncloses, with many other items. The remainder of the plants I am working with, with a view to see if there is any other point so connected with the bristles on the upper surface of the leaf-trap—the seemingly nervous centre—so that I can make any perceptible effect upon this centre.

One plant has caught two of the sprawling rose-chafers (Macrodactylus subspinosus). These beetles are quite strong, and one of the fellows escaped from two traps, but was finally captured by a vigorous leaf that closed over him so quickly, there was no space left for his head to get through.2

About two weeks ago a leaf captured a homopterous insect (Metapodius nasulus), nearly as large as the squash-bug (Coreus tristis).3 When caught it emitted a disagreeable odor, peculiar to this class of insects; and to my surprise the leaf opened yesterday in good condition, and there was nothing left of the insect but the shell.

There is something about these plants that attract insects. Honey-bees wander over the earth close to the base of the plant, sipping the moisture, this is not because of lack of moisture otherwhere, and the plants are in close proximity to a flower garden, and beside, the lawn is now covered with white clover blossoms. So I was induced to examine the roots. The bulbs certainly exude a sweetish mucilaginous substance which the bees are after, but how wary they are of the trap, not one has yet been caught.

You asked what kind of insect Dionaea commonly caught. It most commonly catches Dipterous flies, frequently much smaller than the house-fly.4 If a fly is large enough to move a bristle, so as to close the trap, I never saw it escape from a vigorous leaf—one that acts quickly.

I am also continuing my observations on the Droseras, have added one more to my list, D. brevifolia.5

If there is any other point you wish observed, in any of these plants, I will gladly do what I can for you.

Dr. Wood of Wilmington—the only district in which Dionaea grows—is cooperating with me in these experiments.6

Yours most truly | Mary Treat.

CD annotations

1.1 Some time … centre. 1.10] crossed pencil
2.1 One plant … get through. 2.4] scored blue crayon
4.1 Honey-bees … caught. 4.7] scored red crayon
5.1 It … house-fly. 5.2] scored red crayon
6.1 I am … experiments. 8.2] crossed pencil


CD had previously asked Treat for information on the size of insects caught by Dionaea (Venus fly trap), suspecting that small insects were able to escape (Correspondence vol. 21, letter to Mary Treat, 1 January 1873); he argued in Insectivorous plants, pp. 311–12, that it was advantageous to the plants to trap only larger insects.
CD used this observation by Treat as evidence that strong insects could occasionally escape from Dionaea (Insectivorous plants, p. 312).
Metapodius nasulus is a synonym of Acanthocephala femorata, the Florida leaf-footed bug; Cimex tristis, the squash bug, is now Anasa tristis. Both are in the family Coreidae.
CD cited this observation by Treat in Insectivorous plants, p. 313 n.
For CD’s most recent correspondence with Treat on Drosera (sundew), see Correspondence vol. 21, letter from Mary Treat, 28 July 1873, and letter to Mary Treat, 12 August 1873.
Treat refers to Thomas Fanning Wood of Wilmington, North Carolina; Dionaea is native to a few areas in North and South Carolina only.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Sends her observations on Dionaea capturing insects. [See Insectivorous plants, pp. 311–12.]

Letter details

Letter no.
Mary Lua Adelia (Mary) Davis/Mary Lua Adelia (Mary) Treat
Charles Robert Darwin
Sent from
Vineland, N.J.
Source of text
DAR 58.1: 58–9
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9485,” accessed on 6 December 2022,

Also published in The Correspondence of Charles Darwin, vol. 22