What Type of Earthworms Did Darwin Study?

 
Darwin's Earthworms Revisited

Summary

2006

By Kevin R. Butt¹, Christopher N. Lowe¹,Toby Beesley², Ian Hanson³ and Randal Keynes^{4 1}School of Natural Resources, University of Central Lancashire, Preston, PR1 2HE, UK ²English Heritage, Down House, Downe, Kent, BR6 7JT, UK ³Department of Conservation Sciences, Bournemouth University, Poole, Dorset, BH12 5BB, UK ⁴The Charles Darwin Trust, PO Box 31651, London, W11 4YX

Charles Darwin made Down House in Kent his home from 1842 until his death in 1882 and this is where in 1881, he wrote “The Formation of Vegetable Mould through the Action of Worms”. The work described here was based upon passages drawn directly from this book and also grew from descriptions and observations recorded in his papers and letters, that made reference to earthworms at Down House (Darwin correspondence). In addition, as part of a bid to make the area around Down House a World Heritage Site, further sampling was undertaken at sites identified in Darwin’s papers which made reference to earthworms and their activities.

At Down House, general observations were made in addition to systematic sampling in areas of interest. Seleccted areas were either determined from signs of earthworm activity, habitat type or in direct relation to Darwin’s documented work. Sampling for earthworms employed digging and hand sorting of soil, electrical stimulation, use of a mustard vermifuge and observations under objects located on the soil surface. Fifteen earthworm species were found representing all three ecological groupings. Greatest species richness was found in pasture below an ash (Fraxinus) tree (n = 9 species). Greatest earthworm density was present in Darwin’s Kitchen Garden (715 m^-2) with the largest associated biomass (261g m^-2).

The two most abundant earthworm species recorded were Aporrectodea caliginosa and Aporrectodea longa. This was determined from direct sampling and, in the case of the latter, from observations of surface casting across most grassy areas. Lumbricus terrestris, described by Darwin in terms of its behaviour, but not directly named, was located in the grounds of Down House in relatively low numbers. Nevertheless, its diagnostic middens and associated burrows were easily located. At areas surrounding Down House, other investigations confirmed the findings of Darwin over a century before.