Consider the lowly earthworm, burrowing under your feet and eating old leaves. These activities may seem inconsequential, but they can actually create, change, or destroy habitat. “Earthworms can fundamentally change the soils they inhabit,” says U.S. Forest Service research ecologist Mac Callaham. “They can have such significant effects that they’re often called ecosystem engineers.”
The Asian jumping worm (Amynthas agrestis) is one such earthworm. Like many worms, it eats the leaves, twigs, needles, and bark that fall to the forest floor. However, the nonnative Asian jumping worm is unusually voracious and highly invasive in the U.S.
A recent collaboration between scientists at the Forest Service Southern Research Station (SRS) Center for Forest Disturbance Science and Hiroshi Ikeda, an associate professor at the Faculty of Agricultural and Life Science at Hirosaki University, Japan, provides new information about the life history of the Asian jumping worm and suggests that prescribed fire could be an effective management tool for controlling the species. The study was recently published in the journal Soil Biology and Biochemistry and led by Ikeda, who spent a year in Callaham’s lab as a visiting scholar. The Japanese Society for the Promotion of Science provided funding for Ikeda, and the Forest Service International Programs office helped arrange for his visa.
Ikeda, Callaham, and their colleagues collected leaf litter and several hundred Asian jumping worms from the Chattahoochee National Forest, Georgia, and used the materials to reconstruct the forest floor in eight experimental test beds. Each bed had 100 worms in it. Half the plots were burned at low intensities – two inches below the soil surface, the temperature only increased by 14o F – to mimic prescribed fires that might be used by Forest Service managers. The other plots were left unburned as a control. When worms and cocoons (which are similar to eggs) were collected after the fire, researchers found approximately the same number in each type of plot.
However, cocoons from burned plots were much less likely to hatch. “Although the fires did kill some adult worms, it looks like most of them can burrow deeper into the soil to avoid the fire,” says Callaham. “But because the earthworm cocoons are laid near the soil surface and can’t move away from the heat, they don’t survive nearly as well.” Since the cocoons represent the next generation of adult earthworms, destroying them could help reduce populations. Asian jumping worms usually produce cocoons by early fall, so the most effective time for using prescribed fires to control them would probably be in October or later.
To find out whether the worms could use recently fallen, fresh litter (large particle size), or if they needed to have partially decomposed, older (and smaller particle-sized) material for their nutrition and reproduction, scientists set up seven treatments with different types and sizes of food particles, as well as the amount of soil mixed in. “We found that the earthworms don’t have a strong preference for the size of the litter,” says Callaham. “As long as a mix of litter and soil is available, the worms produce large numbers of cocoons. In addition to the negative effects on cocoons, removing the food source with prescribed fire seems like it might be an important part of the puzzle of managing these invasions.”
“Biological invasions are one of the most significant global-scale problems caused by human activities,” says Callaham. “Although most of the attention has gone towards vertebrates or plants, earthworms can dramatically change soils, in turn affecting other soil invertebrates, and ultimately plant and animal communities.”
For more information, email Mac Callaham at firstname.lastname@example.org