The Invisible Forest

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Published on: Jun. 2, 1999

Last revision: Nov. 2, 2010

so it can easily escape predators and move from litter patch to litter patch in search of food.

Box mites, which average 400 individuals per square meter, belong to a group of arachnids (eight-legged arthropods--mites, ticks, spiders and harvestmen) called oribatid mites. Unlike other arachnids, oribatids are herbivorous. Together with the springtails, the oribatids help speed up the rate of decomposition by feeding on dead plant material and fungi.

Oribatids also are interesting because their exoskeletons are hardened with calcium carbonate. The shell-like exoskeletons help protect the slow-moving oribatids from predators. The box mite has taken this innovation one step further by closing the shells covering its body the same way a box turtle does, so that its soft parts are completely protected.

One of the predators the oribatids must protect themselves from are mesostigmatid mites, which average over 900 individuals per square meter. Like most litter species, this one still needs to be identified by a taxonomist. Until then, it is known to us as species #154. Its mouth parts are needlelike, adapted for exploiting any cracks in oribatid exoskeletons.

Pseudoscorpions are another important predator. These animals also are arachnids. Their name comes from the two large claws at the front of the body that give them the appearance of scorpions. However, there is no stinging tail, so pseudoscorpions rely on the dexterity of their claws to capture prey. They average 300 individuals per square meter.

Both mesostigmatid mites and pseudoscorpions feed on springtails, insect larvae and other arachnids--anything they are able to catch and hold onto.

Together these five species make up 30 percent of the total number of individuals in the leaf litter. This may suggest that leaf litter is a pretty simple community composed of only a few species, but we typically find over 50 species in each sample, and we have distinguished over 800 species altogether.

Sometimes, as I am looking at a new sample, I can't help thinking of an African landscape. Swift and active surface-dwelling springtails remind me of antelope, the abundant and deep-dwelling springtails and fly larvae burrow into the litter like rodents into soil, the stolid and slow moving oribatids graze through the litter like hippos through a marsh, and the predatory mites, pseudoscorpions, spiders, beetle larvae and ants, stalk their prey like lions, jackals and hyenas. The same dramas that unfold in the African savanna are played out a hundred times a day in each of our

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