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Soil fauna in the food web

NORTH CAROLINA — Imagine walking through a forest with leaves crunching beneath your feet. Underneath those crunchy leaves is a complex ecological realm. “Soil is teeming with life,” says Forest Service research ecologist Mac Callaham. “Most people don’t think about it because they don’t see the soil fauna.”

Soil fauna includes centipedes, millipedes, springtails, nematodes, insect larvae and earthworms. “Springtails are very small arthropods,” says Southern Research Station ecologist Melanie Taylor. “Earthworms are the giants of soil fauna.”

Taylor, Callaham and lead author Meixiang Gao recently published a study on non-native earthworms and the food web in the journal Soil Biology and Biochemistry.

Gao is a Chinese scholar who spent a year with Callaham’s research group in Athens, Georgia. “Gao and I spent a lot of time in the car,” says Taylor. “We drove to various places on the Chattahoochee-Oconee National Forest several times to collect soil fauna for this study.”

They collected centipedes and Asian jumping worms, Amynthas agrestis. They also raised springtails in the lab. Like every living organism, the three species are part of a food web.

“It’s difficult to study soil food webs,” says Taylor. “For one thing, many of the participants are really small, and it’s hard for us to see them. There’s also a lot of plasticity in what soil fauna eat.”

The researchers added soil, leaf litter and various combinations of the three species to plastic containers. They wanted to see if earthworms affect the relationship between centipedes and springtails.

Over a six-week period, the researchers dumped out the soil three times and counted all the inhabitants. They were surprised to learn that centipedes were preying on the earthworms. Some of the earthworms weighed 10 times as much as the centipedes.

“It’s a David and Goliath situation,” says Callaham. “But David is very well-armed. Centipedes have venomous fangs that deliver neurotoxins, muscular toxins, all kinds of bad things. And they’re fast. They’re like the lions of the soil food web.”

Earthworms are not very leonine. They are mostly vegetarians that tunnel through the soil eating leaf litter. However, their presence affected springtails.

“When earthworms were present, springtails didn’t fare very well,” says Taylor. “It’s not clear why. Earthworms could be eating springtail eggs as they move through the soil. Or maybe they’re competing with them for food.” When earthworms were present, springtails still reproduced, but at lower rates.

Photo: Close-up of earthworm in gloved hand.
Earthworms are mostly vegetarians that tunnel through the soil eating leaf litter. Forest Service photo.