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Darwin Correspondence Project

From J. H. Comstock   4 June 1880

J. Henry Comstock. | Entomologist to the | U.S. Department of Agriculture. | Washington, D. C.,

4 June 1880.


Mr. Charles Darwin, | Farnborough Hants, Kent Co., England.


I have requested that a copy of my Report on Cotton Insects, recently published by this Department, be sent to you.1 Knowing that your time is fully occupied I take the liberty of indicating the parts of the Report which I think will be of interest to you. The cotton worm (Aletia argillacea) is doubtless a tropical insect which has been introduced into our territory; as yet however, it is not fully naturalized and but very few are able to survive our winter.2 Thus the first brood in the spring is so small that it is seldom noticed (see p.97). In the course of the season the insect passes through several generations, frequently increasing in numbers to such an extent as to sweep away the entire cotton crop of large sections of country. But of the immense numbers thus produced only a few individuals ever survive the following winter (see pp.90, 91). Is not this a remarkable instance of the action of natural selection where hardly one insect in five hundred thousand is preserved?

Another point which I think will be of interest to you is the structure of the maxillae of the adult Aletia (see pp.86,87).3

I think you will also be interested in the extra floral nectar glands to which I have referred on pp.84,85 and which are discussed more at length by Mr. Trelease pp.319–333.4

Yours very respectfully | J. Henry Comstock.


An annotated copy of Report upon cotton insects (Comstock 1879) is in the Darwin Library–CUL.
Aletia argillacea is a synonym of Alabama argillacea (cotton leafworm or cotton worm). It is a moth of the family Erebidae (the same family as the moth described in F. Darwin 1875; see n. 3, below).
In Comstock 1879, p. 87, Comstock cited F. Darwin 1875 and Orchids. Comstock had noted that in the adult moth, the maxillae possessed spines on the dorsal surface, enabling the organs to be used to pierce fruit. Francis Darwin had discussed similar adaptations in a related moth, Ophideres fullonica (a synonym of Eudocima phalonia, the Pacific fruit-piercing moth).
Comstock 1879, pp. 319–33, was a chapter by William Trelease, ‘Nectar; what it is, and some of its uses’. It was followed by an extensive bibliography, including Cross and self fertilisation and Variation. Passages on these pages are scored in CD’s copy (see Marginalia rev. ed.).


Comstock, John Henry. 1879. Report upon cotton insects, prepared under the direction of the Commissioner of Agriculture in pursuance of an act of Congress approved June 19, 1878. Washington: Government Printing Office.

Cross and self fertilisation: The effects of cross and self fertilisation in the vegetable kingdom. By Charles Darwin. London: John Murray. 1876.

Darwin, Francis. 1875b. On the structure of the proboscis of Ophideres fullonica, an orange-sucking moth. Quarterly Journal of Microscopical Science n.s. 15: 384–9.

Marginalia rev. ed.: Biodiversity heritage library: Charles Darwin’s library.

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Summarises points of interest in his Report upon cotton insects [U. S. Dept. of Agriculture, Bureau of Entomology (1879)].

Letter details

Letter no.
John Henry Comstock
Charles Robert Darwin
Sent from
U.S. Dept of Agriculture, Washington
Source of text
DAR 161: 217
Physical description
TLS 2pp

Please cite as

Darwin Correspondence Project, “Letter no. 12621,” accessed on 24 May 2022,