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Darwin Correspondence Project

From Francis Galton   7 March 1881

42 Rutland Gate

March 7/81 | Monday morng.

Dear Darwin

About Worms:— I have waited for an opportunity of verifying what I told you about the effect of heavy soaking rain, when it suddenly succeeds moderate weather, in driving the worms from their holes to the gravel walks, where they crawl for long distances in tortuous courses, & where they die.1 It has been very frequently observed by me in Hyde Park & this morning, I have again witnessed it in a sufficently well marked degree to be worth recording.

It rained heavily on Saturday night last, after a spell of moderate weather. Unluckily I was not in the Park on Sunday till near 1h., by which hour the birds had had abundant time to pick up the worms. Still, dead worms were about & their tracks were most numerous. On Sunday (last night) it again rained heavily & I was in the Park at 10h. The tracks were not nearly so numerous as they had been on Sunday morning, but more dead worms were about. I began counting, & found they averaged 1 to every 212 paces (in length) of the walk, the walk being 4 paces a trifle more in width.

Walking on, I came to a place where the grass was swamped with rain water on either side of the raised gravel path, for a distance of 16 paces. In those 16 pace-lengths I counted 45 dead worms.2

On not a few previous occasions when I have been out before breakfast, I have under the conditions already mentioned seen the whole of the walks strewn with worms almost as thickly as were the 16 pace-lengths first described. The worms are usually very large. I rarely notice dead worms on the paths at other times

Ever sincerely yrs | Francis Galton

I shall be very curious to learn about the effects of the red light as against those of a strongly actinic colour3


CD may have seen Galton while he was in London from 24 February to 3 March 1881 (see CD’s ‘Journal’ (Appendix II)).
CD added Galton’s information about dead worms in Earthworms, p. 14.
Actinic light contains a high proportion of ultraviolet rays. CD had tested the sensitivity of worms to red and green light; his notes on the subject, dated 23 October 1880, are in DAR 64.1: 54. CD noted that worms did not appear to be sensitive to the amount of light passed through filters of dark red and blue glass, and that the colour did not seem to make any difference to their reaction.


Earthworms: The formation of vegetable mould through the action of worms: with observations on their habits. By Charles Darwin. London: John Murray. 1881.


Reports observations of worms for CD’s use.

Letter details

Letter no.
Francis Galton
Charles Robert Darwin
Sent from
London, Rutland Gate, 42
Source of text
DAR 105: A106–7
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 13076,” accessed on 19 August 2022,