Over time, leaves are broken down by fungi, bacteria and other detrivores (organisms that eat dead stuff) like earthworms. The superpower of the earthworm (Lumbricus terrestris) is its ability to compost vegetation and return vital nutrients to the soil.
Charles Darwin was fascinated by earthworms, conducting wonderful experiments to determine how much soil they moved and whether worms preferred to collect leaves from the broad end or pointed end. Worms pull leaves into their burrows (narrow end first) to plug the opening and protect themselves from ‘early birds’.
In much of North America, earthworms were killed off in the last ice age (~10,000 years ago). The worms you see now in Michigan, Maine and Minnesota are all invaders. Sounds great, right? More nutrients in the soil? Unfortunately, the northern hardwood forest ecosystem is adapted to a thicker leaf litter layer and slower release of nutrients. So now, the introduction of the earthworm changes which seeds can germinate (and which trees will continue to survive), nutrient run-off, and which animals live in the new, de-littered forest. (1)
If you’re interested in appreciating the awesome recycling power of the worm, check out a delightful little book by Amy Stewart – “The Earth Moved: On the Remarkable Achievements of Earthworms”.
Want to read more specifics about leaf-earthworm experiments? Natural History Magazine has an entertaining write-up.
- Hale CM et al. 2008. Exotic earthworm effects on hardword forest floor, nutrient availability and native plants a mesochosm study. Oecologia. 155:509-518.