Mature individuals of Octodrilus complanatus were obtained by soil sorting from a maize field in Cesantes (Galicia, Spain) and kept in 1-L plastic containers filled with field-collected soil and fed with cow manure added to the surface. Soil moisture content was maintained at 25% with tap water twice a week. Cocoons were hand-sorted weekly from these initial stocks, measured their weight and size, and then incubated at 20±2°C until hatching. Hatchlings were kept individually in 250-mL plastic vessels with soil, and fed with cow manure ad libitum; the vessels were maintained in a scientific incubator at 20±2°C. The weight of the earthworms and their sexual maturation were recorded weekly; we considered that earthworms attained sexual maturation when the clitellum was fully developed. Results were analyzed by the Student's t test. Data are shown as means ± SE.

The growth of O. complanatus followed a sigmoid curve, with a slow initial phase (1.03±0.03 g of weight in 75 days) and a rapid phase until sexual maturation (5.1±0.2 g of weight in 75 days) (Fig. 1). Earthworms matured sexually after 150 days with a mean weight of 6.1±0.2 g, and the stationary growth phase was reached after 210 days, with a mean weight of 8.2±0.2 g. The growth rate of earthworms was significantly higher before than after sexual maturity, 43.9±1.8 and 27.6±2.8 mgday−1, respectively (t Student test; t=5.74, d.f.=29, P<0.0001).

Cocoon production started 34±3 days after mating and their reproduction rate was 0.82±0.14 cocoons per earthworm per week. Cocoons were characterized by a mean mass of 92±4 mg and a size of 6.9±0.1 mm (length) and 4.8±0.3 mm (wide). Incubation time (at 20 °C) of these cocoons was 66±2 days (range 50 to 70; n=30), but hatchability was only 55% under culture conditions. Only a single hatchling emerged from each cocoon, with a mean biomass of 82±3 mg (range 60 to 100 mg; n=30).

In laboratory conditions, O. complanatus showed an unexpectedly high growth rate according to their ecological type, characterized by lower growth rates and maturation time [5–7]. This unexpected growth was probably due to the increased food availability and temperature, since Lee [3] reported an optimal thermal range for European lumbricids between 10–15 °C; these results are supported by lower growth rates in Lumbricus terrestris at 10–15 °C than at 20 °C, as reported by Butt et al. [6]. Apparently, there is a contradiction between the high rates of growth and reproduction that we found at 20 °C in this work and the halt in reproduction that this species experiences during summer. In fact, analysis of mature individuals of O. complanatus obtained from field populations revealed that in summer the ovaries were not well developed; the size of the seminal vesicles was smaller than during the rest of the year, and the spermathecae were empty, showing a reduced diameter [8,9]. These characteristics were the result of the combination of low moisture conditions and high temperatures, which does not occur in laboratory conditions. Therefore, there is need for further research on variation of the life traits of this species in a range of temperatures and moistures, in order to apply our knowledge to field conditions.

The life cycle of O. complanatus, showed in Fig. 2, is more similar to those of other large anecic or endogeic earthworms, like Lumbricus terrestris, L. friendi, and Allolobophora caliginosa (k-selected species) than to the life cycles of epigeic earthworms like Eisenia fetida, E. andrei, Eudrilus eugeniae and Perionyx excavatus, with shorter sizes, fast growth and higher reproductive rates (r-selected species) [10]. Thus, similar growth rates were found by Butt [5] and Butt et al. [6] for L. terrestris (6 g of weight in five months at 20 °C), even though they were higher than the growth rates of Allolobophora longa, Octolasion cyaneum, and Allolobophora carpathica, other deep-burrowing species [5,7]. The rate of cocoon production (52 cocoons per earthworm per year) places O. complanatus together with species like L. terrestris, A. longa, A. carpathica and O. cyaneum (38, 18, 10 and 32 cocoons per earthworm per year, respectively); however, the cocoon incubation time, over 60 days, and hatchability (55%) were slightly lower than those recorded in L. terrestris and O. cyaneum and similar to A. longa's ones [5,7].