Implications of ecological parameters on earthworm diversity and abundance in southwestern Nigeria

A survey on the diversity and abundance of earthworms in southwestern Nigeria was carried out. Earthworm and soil samples were collected from thirty different locations within the sub-region. Earthworms were identified and soil samples were analysed for mineral and metal loads, using standard procedures. Taxonomic analysis of collected earthworm samples revealed 24 species belonging to eight families namely Moniligastridae, Megascolecidae, Acanthodrilidae, Octochaetidae, Ocnerodrilidae, Eudrilidae and Almidae. These include some genera and species that are reported for the first time from Nigeria. Analysis of earthworm biomass showed that Libyodrilus violaceus had the highest biomass (104.4g/m2) while Hyperiodrilus africanus had the highest density (160 worms/m2). Earthworm biomass correlated negatively but significantly with pH (p<0.01). Analysis of earthworm abundance in relation to soil types indicates that E. eugeniae was present in all seven soil types studied, while only Alma millsoni and H. lagosensis can be used as indicators of ferruginous tropical soils and red-yellow ferralsols. Earthworms from this study revealed affinity for various combinations of sand and loam soils. The present results revealed a decline in earthworm abundance when compared with previous works. This work revealed the need to harness the habitat factors, which support earthworm abundance for use in both earthworm and soil conservation efforts.