A test of the ‘hot’ mustard extraction method of sampling earthworms

Earthworm densities in soil are difficult to quantify. Part of the problem is that they are incorporated closely into the soil structure, which makes their extraction tedious and time consuming (Edwards, 1991). In addition, earthworms have widely varying patterns of activity and occupy a range of soil depths depending upon season, species, and life history stage (Bouche and Gardner, 1984). Behavioral methods, which involve stimulating earthworms with a chemical or other expellant (e.g. an electrical shock) and collecting them as they emerge at the surface, have been proposed as efficient extraction methods that do not require physical disruption of the soil system. We examined the effectiveness of one such technique: the non-toxic ‘hot’ mustard extraction method. We compare hot mustard extraction with digging and hand-sorting, and conclude that it provides a consistent index of earthworm abundance across a range of soil and land-use types.