Gut load and food-retention time in the earthworms Lumbricus festivus and L. castaneus: A field study

Summary Lumbricus festivus and L. castaneus consume dung. In the field, below cow pats, their gut loads were about 0.15 and 0.14 g dry weight g^-1 ash-free dry weight of worm, respectively, but in free soil the loads were higher, about 0.21 and 0.19 g g^-1 ash-free dry weight of worm. The gut contents of dung were lighter than the total ingested material, at about 0.10 and 0.07 g dry weight g^-1 ash-free dry weight of worm, respectively. Field experiments showed that the retention time of dung ranged from >9 to 15 h for L. festivus, and from >3 to 6 h for L. castaneus. The experiments also indicated that L. festivus exploited 20- and 36-day-old dung in different ways, since the gut load was lower in those worms consuming 20-day-old dung than in those consuming 36- to 40-day-old dung. On the basis of these results the calculated consumption rate for L. festivus is 0.08 g dung day^-1 g live weight of worm^-1, and for L. castaneus 0.15 g dung day^-1, with retention times assumed to be at maximum, 15 h, for L. festivus and 6 h for L. castaneus. These calculations indicate that our field population of worms (75 g m^-2) consumes 10–15 t dung ha^-1 180 days^-1, corresponding to the amount of dung produced by 2–3 dairy cows.