Sims, R.W. and Gerard, B.M. 1999. Earthworms. Synopses of the British Fauna (Eds. Barnes and Crothers). Field Studies Council, Shrewsbury.
Edwards, C.A. and Bohlen, P.J. 1996. Biology and Ecology of Earthworms (3rd Edition). Chapman and Hall, London.
Darwin, C. 1881. The formation of vegetable mould through the action of worms. John Murray, London.