Earthworm biomass: Influence of gut content and formaldehyde preservation on live-to-dry weight ratios of three common species of pasture lumbricidae

Abstract

Allolobophora caliginosa (Savigny), A. trapezoides (Duges) and Lumbricus rubellus Hoffmeister were reared on enriched sandy soil. Live and dry weights, and weights after preservation in 5% formaldehyde were determined for worms with and without gut contents. Quadratic regressions of the log transformed weights gave a significantly better fit than linear regressions for the relationships between live weight including gut contents, and either dry weight with an empty gut or dry weight with gut contents. Intermediate size worms had the highest proportion of gut contents. The dry weight of gut contents as a proportion of live weight could be more easily and accurately calculated from the difference between dry weights with and without gut contents averaged over size classes defined by the log of the weights of live worms. Dry weight minus gut contents, the best standard for biomass can be determined from field samples perserved in formaldehyde by combining linear regressions predicting live weight from formaldehyde weight which are independent of gut contents, with linear regressions predicting dry weight minus gut contents from live weight with gut contents. Because the density of the gut contents affects the latter regression it should be determined from a subsample of worms of each species on each sampling occasion.