Reproduction and population dynamics of the earthworm <i>Eisenia fetida</i> (Savigny, 1826) in a semi-arid region: The case of Khouribga wastewater treatment plant (Central Morocco)

Eisenia fetida (Oligochaeta, Lumbricidae), an epigeic species thriving in environments rich in organic matter, is highly abundant in the wastewater spreading area of Khouribga City, Central Morocco. This study, conducted over an annual cycle (January to December 2022), investigated the reproduction and population dynamics of E. fetida. The population exhibited high density (742 ± 474 ind./m²) and biomass (274.90 g/m²), with four stages of maturity present year-round, though their proportions varied seasonally. Two reproduction periods were identified: the first spanning January to late April, and the second beginning in late September and persisting throughout the year. Population density peaked in April and October. The average fresh weight of mature individuals ranged from 0.26 to 1.22 g, while the number of cocoons per mature earthworm varied between 0.28 and 12. Furthermore, larger adult worms produced more cocoons than smaller ones and cocoon size ranged from 3.94 to 37.27 mg per unit. The annual production in 2022 was 337.95 g/m², yielding a production-biomass ratio (P/B) of 1.23. Because of its favorable demographic and ecological traits, E. fetida is a promising species for treating sludge from wastewater treatment plants.