Ranges and Cold Hardiness of Two Earthworm Subspecies (Eisenia nordenskioldi, Lumbricidae, Oligochaeta)

The ranges of two earthworm subspecies, Eisenia nordenskioldi nordenskioldi (Eisen 1879) and E. n. pallida Malevic 1956, differ in area and partially overlap. E. n. nordenskioldi populates the entire Asian Russia and eastern regions of the Russian Plain, from the lower reaches of the Volga and Don rivers to the Arctic Ocean coasts, while E. n. pallida has not expanded to the Asian permafrost zone and does not occur in European Russia and in the Urals. These subspecies "hold the record" in cold hardiness: the worms and cocoons of the nominotypical subspecies withstand temperatures down to -34 and -40 degrees C, and those of E. n. pallida, to -28 and -23 degrees C, respectively. Hence, their distribution is independent of subzero temperatures, and their ability to overwinter at any phase of the life cycle makes them also independent of heat supply during the summer period. Differences in geographic range may also be due to biological features of the subspecies. The nominotypical subspecies feeds belongs to the epiendogeic morphoecological type (feeding on the ground surface), whereas E. n. pallida is a true endogeic earthworm. Both subspecies have similar requirements for soil acidity; however, conditions in coarse-humus organomineral horizons of frozen soils appear to be unfavorable for E. n. pallida, which accounts for the absence of this subspecies in the permafrost zone.