Invasive Earthworms in the Food Web

Unexpected effects on Centipedes and Springtails

springtails
Springtail abundance was reduced by  earthworms but not centipedes. Photo by Steve Nanz.

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 U.S. 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 SRS 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. The study was published in the journal Soil Biology and Biochemistry.

Gao is a Chinese scholar who spent a year with Callaham’s research group in Athens, GA. “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.”

Listen to a brief audio clip by author Melanie Taylor describing this publication. • Text Transcript

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.

Usually, that relationship is pretty simple – springtails try to hide, and centipedes try to eat them.

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.

Amynthas agrestis
Previous SRS studies have shown that prescribed fire can kill Asian jumping worm cocoons. Photo by Tom Potterfield, CC 2.0.

“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.

It’s one more reason Asian jumping worms are an unwelcome guest in Southeastern forests.

“Asian jumping worms are so voracious that they change the composition of the forest floor,” says Taylor. “Because of their tremendous effects on soils, they’re sometimes called ecosystem engineers.”

Eventually, the research will help national forest managers know how to control the invasive worms. “The body of work on the Asian jumping worm is growing,” says Callaham. “We hope we can provide control recommendations soon.” Callaham has studied earthworms for years, and one of his previous studies showed that prescribed fire can kill worm cocoons.

Asian jumping worms and other non-native earthworms are often sold online. “The provenance of these worms is uncertain in the best case,” says Callaham. “Most are non-native. And they won’t stay in the compost bin. The best way to prevent future invasions is to avoid moving earthworms around.”

Read the full text of the study.

For more information, email Melanie Taylor at melanietaylor@fs.fed.us.

Access the latest publications by SRS scientists.

 

Subscribe to our newsletter!

Receive weekly updates