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Earthworm cocoons: The cryptic side of invasive earthworm populations

Nouri-Aiin, Maryam, Görres, Josef H.
Applied soil ecology 2019 v.141 pp. 54-60
annuals, autumn, cocoons, earthworms, embryogenesis, hardwood forests, hatching, horticulture, overwintering, spring, summer, winter, Vermont
Asian earthworms in the pheretimoid group are currently invading hardwood forests in the northeastern USA. Population studies of these earthworms typically focus on life stages after hatching. However, the more cryptic part of these populations, cocoons, has largely been ignored. This paper is concentrating on cocoon abundance of two pheretimoid species through the year, and on identifying their readiness to hatch as determined by the presence of embryos that were well-advanced in their development. We wanted to know when viable cocoons were present and what their embryonic development was. We found that unhatched cocoons and ready-to-hatch embryos were present all year round. At the Horticultural Research Center of the University of Vermont, A. tokioensis cocoon abundance (mean ± standard error) varied between 1203 ± 167 m−2 in the winter and 498 ± 79 m−2 in the summer. Here A. agrestis varied between 439 ± 62 m−2 in the spring and 722 ± 70 m−2 in the fall. At another site dominated by A. agrestis, cocoon abundance varied between 753 ± 150 m−2 in the spring and 1386 ± 167 m−2 in the winter. Cocoon production was estimated at about 0.6 cocoons per worm per day. We raise the question whether cocoons have a longer-term survival function beyond overwintering of the population, akin to the function of the seed bank of annual plants.