It would make a great scene in a nature movie. As the cameras roll, the stealthy predator lurks unseen behind some dead vegetation. A grazer ambles by, munching away, clueless to the nearby threat. The predator pounces. The victim struggles, twitches, then succumbs.
Later, a scavenger picks over the grazer’s remains, and – hey, how did that giant shoe get in the frame? Cut!
Of course, the shoe isn’t giant-sized. It’s the nature scene that is tiny. It’s literally underfoot every time you walk in the forest. Leaf litter (which is mostly leaves, but also twigs and seeds) can seem like nature’s garbage, but it is actually a thriving ecosystem whose miniature players have a vital role in the more familiar, larger forest ecosystem populated by deer, bobcats, owls, and snakes.
In the role of predator, the leaf litter ecosystem has spiders. But we’re not talking here about the orb spiders that build beautiful webs across the door of the woodshed. Among the types of spiders commonly found in leaf litter are jumping spiders, wolf spiders and sac spiders. Centipedes, not quite as dominant in the leaf litter as spiders, are nonetheless capable hunters.
The most abundant invertebrates in leaf litter are springtails and mites. While both of these groups of creatures could be called bugs, as in “creepy little living things that I really don’t want to find in my breakfast cereal,” neither are insects.
Mites are arachnids, in the same family as spiders. Springtails are hexapods, which were recently thrown out of the taxonomic class of insects. (Just couldn’t keep their grades up, I guess.) Yup, your field guide still calls them insects (at least mine does), but chances are in the next printing, they won’t be insects anymore.
Mites have eight short legs and unsegmented bodies. One important group of mites found in leaf litter are the oribatid mites. Oribatid mites are small, dark, shiny and hard. They eat bacteria, yeast, algae, fungi and rotting wood. Other types of mites are predators, eating smaller creatures including springtails and other mites.
Springtails are a little bigger. They have six legs and eat fallen leaves, algae, and fungi. Not all springtails have the forked springing organ that allows them to jump amazingly far. But those that do have that organ are among the springtail species you see gathering on top of the snow in late winter.
A square yard of forest soil may contain hundreds of thousands of individual mites and springtails. (And aren’t you glad you weren’t the one who counted them?)
Fungi and bacteria eat the leaves. Mites and springtails eat the fungi and bacteria. Spiders and centipedes eat the mites and springtails. Salamanders and mice eat all sorts of bugs while living in and under the leaf litter. Snakes eat the salamanders. Owls and foxes eat the mice. That’s just six degrees of separation between a layer of leaves on the forest floor and the owl hooting outside your bedroom window.
But all is not happy in Leaf Litter Land. Aliens have landed and are gobbling the scenery, stealing food from the decomposers and leaving the rest of the residents with no place to hide. You know these aliens. They are earthworms.
Sure, in the garden (or on a fishhook), earthworms are the good guys. Earthworms aerate the soil and turn organic debris (such as leaf litter) into nutrients plants can use. That’s great – in a garden.
The last glacier (which retreated 10,000 years ago) ground the native earthworms of New Hampshire and Vermont into wormburgers. Since the glacier melted, Southern earthworm species have not yet recolonized the northeastern United States.
The earthworms found in Vermont and New Hampshire today are species native to Europe and Asia. Some may have stowed away in ship ballast or the root balls of imported plants. Some were brought over deliberately, to condition the soil for garden plants, many of which are native to (you guessed it) Europe and Asia.
Our forests evolved without earthworms. Their systems work best without all the air, moisture, and nutrients in the soil that the earthworms introduce. Plus, that thick layer of leaf litter that the earthworms chew through so quickly is home to a vital ecosystem of its own.
Nothing seems more dead than a layer of fallen leaves on the forest floor. Yet it is very much alive, not just with the decomposers you’d expect, but a whole food chain’s worth of hunters and browsers – even alien invaders. And, if you can keep your giant shoes out of the way when they make that nature film about it, that would be great.