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Darwin Correspondence Project

To Mary Anne Theresa Whitby1   2 September [1847]

Down Farnborough Kent

Sept 2d

Dear Madam

Your great kindness in giving me last year at Southampton2 information on the varieties on the silk-worm, makes me venture once again to trouble you. My question is a very simple one, and yet I am very curious to have it answered on the best authority.— Whenever I have observed the moths raised from silk-worm kept by children, the wings have been more or less crumpled, & I have been assured that they can never fly. Does this hold good, especially in France & Italy? If it does, can you, inform me, whether the males & females are equally helpless as regards flight?3 I presume that they are in the same condition, as our domestic ducks, & I should be extremely grateful for any information on this point.—

You were so kind last year as to give me hopes that you would try two experiments on hereditariness (a point on which I am particularly interested) in the caterpillar state: the first was whether the black eye-browed kind would produce black or dark-eyed caterpillar children:4 the second was to see if the very fat caterpillars (which I think you called Frales & which you described to me in a very laughable manner) would produce moths; & if so whether their offspring would be likewise fat & silkless.—5 I can really hardly say, how grateful I should be to know the results of such experiments; for in a work which I intend some few years hence to publish on variation, there will be hardly any facts in the insect world.

Will you permit me one other question, namely whether you have ever observed any difference in habits, such as in manner of crawling, eating, spinning &c in the caterpillars of the different breeds, which you have kept.— I am well aware I have much reason to apologise for thus presuming to trouble you, & I can only trust to your kindness to excuse.

Pray believe, dear Madam, with much respect. | Your sincerely obliged | Charles Darwin


Mrs Whitby is identified from CD’s reference to their correspondence in Variation 1: 302–3. For biographical information about her, see Colp 1972.
Mrs Whitby, an expert on silkworm cultivation, read a paper on the subject at the Southampton meeting (1846) of the British Association (Whitby 1846; see also Whitby 1848). CD attended this meeting.
CD cited Mrs Whitby on this subject in Variation 1: 303. He stated that although both sexes have imperfect crumpled wings and are incapable of flight, she had assured him that ‘the males of the moths bred by her used their wings more than females, and could flutter downwards, though never upwards’.
CD reported that Mrs Whitby’s experiments confirmed that the character was inherited (Variation 1: 302).
CD referred to this request again in his letter to M. A. T. Whitby, 12 August [1849]. In Variation 1: 303, he stated that Mrs Whitby was prevented by an accident from carrying out the experiment. The term ‘frales’ does not occur in either Whitby 1846 or 1848, but it is apparently what she called silk worms that ‘will not be induced to spin … yet become yellow, but fat and heavy’ (Whitby 1848, p. 25) and which could be used for producing long round silk threads (‘Florence’ or ‘silk-gut’) by drawing out the intestinal canals after soaking the worms in vinegar and water (Whitby 1848, pp. 43–4). The English dialect dictionary (Joseph Wright ed., Oxford: 1900) defines ‘frail’ as: ‘A term used by spinsters … denoting that from unskilful hemming, the threads pull out lengthways.’


Colp, Ralph, Jr. 1972. Charles Darwin and Mrs. Whitby. Bulletin of the New York Academy of Medicine 2d ser. 48: 870–6.

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

Whitby, Mary Anne Theresa. 1846. On the cultivation of silk in England. Report of the 16th meeting of the British Association for the Advancement of Science held at Southampton, pt 2, pp. 87-8.

Whitby, Mary Anne Theresa. 1848. A manual for rearing silkworms in England: with a brief notice on the cultivation of the mulberry tree. London.


Questions Mrs W on difference in flight capacity of male and female silkworm moths and asks her for results of experiments he suggested she do with silkworms to determine hereditariness of dark "eyebrows". [See Variation 1: 302.]

Letter details

Letter no.
Charles Robert Darwin
Mary Anne Theresa Whitby
Sent from
Source of text
American Philosophical Society (Mss.B.D25.61)
Physical description
ALS 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 1113,” accessed on 14 April 2024,

Also published in The Correspondence of Charles Darwin, vol. 4