Laboratory studies on the life-histories of four enchytraeid worms (Oligochaeta) which inhabit sewage percolating filters

The life-histories of four enchytraeid worms, Lumbricillus rivalis, Enchy-traeus coronatus, E. buchholzi, and E. albidus which occur in sewage percolating filters, were studied under laboratory conditions at 8 , 15 and 20°C. The number of ova per cocoon varied from 0 to 50 (L. rivalis), 0 to 33 (E. coronatus), 1 to 9 (E. buchholzi) and 0 to 22 (E. albidus). The mean number of ova per cocoon was highest at 15°C for all species except E. coronatus which had a highest mean value at 8°C. The number of ova in cocoons was correlated with cocoon length (P < 0.001) for all species. Cocoon production usually increased with temperature ranging from 0.8 cocoons per adult per week at 8°C to 2.0 at 20°C for L. rivalis, and from 1–4 to about 2.6 for E. coronatus and E. buchholzi. The total number of ova produced by each E. coronatus (350 at 8°C to 550 at 20°C) was similar to that produced by each L. rivalis (600 at 8°C to 350 at 20°C) and was about five times greater than the total numbers produced by the other two species. Cocoon and ova production and the number of ova per cocoon varied with the age of the adult, usually reaching a peak soon after maturity. Hatching success was low and generally 40–50 % of ova failed to develop; subsequent mortality among immature worms was about 10–20%. Growth was more rapid at the higher temperatures; L. rivalis matured in about 26 days at 20°C, the clitellum forming when the worm was 13–14 mm long; data for the other species are 13 days and 5–6 mm (E. coronatus); 16 days and 3–4 mm (E. buchholzi); 28 days and 13–14 mm (E. albidus). The maturation period at 8°C was at least twice that at 20°C. The generation period (cocoon to cocoon) was about a month at 20°C for all species except E. albidus (2 months), but as some species had longer reproductive periods than others the actual number of generations per year was highest in E. buchholzi, 7.0 per year, and lowest in E. albidus, about 3.3 per year, At 8°C all four species had between 1.4 and 2.8 generations a year. A comparison of expected and observed population densities of L. rivalis and E. coronatus in a sewage percolating filter showed that neither achieved values approaching their potential summer densities although ample food was apparently available. Of the four species studied only E. buchholzi produced viable ova without pairing.