Adapting to Invasive Jumping Worms

Having positively identified jumping worms (Amynthas spp. and Metaphire spp.) in my garden and the surrounding woods, I have been researching plants that are both vulnerable to and potentially resilient against these invasive species. Jumping worms consume the leaf litter, or "duff," along with other organic matter, in the top few inches of the soil's horizon. They degrade the soil’s structure, leaving the roots of plants susceptible to desiccation and the earth prone to erosion. Worm castings with the texture of coffee grounds are a clear sign of their presence. In the pebbly, dry, depleted soil left by these pests, seeds struggle to find an anchor as they begin to germinate, and plants have difficulty accessing the nutrients they need.

Infestations of jumping worms have spread through much of the Northeast. To date, most management plans focus on preventative practices, such as using bare-root plants instead of potted ones or avoiding the spread of the worms and their cocoons by not transporting soil and mulch. These products are only safe when they have been solarized or heat treated to kill worm cocoons. Scant research exists on surefire strategies gardeners can employ to confront jumping worms once they are established. There is no silver bullet, so what can gardeners do to adapt to these invasive pests?

Some plants in my garden appear to be doing better than others. The native honeysuckle vines (Lonicera sempervirens) are thriving, but a drift of bee balm (Monarda didyma) struggled last summer. Yet it would be presumptuous to make the leap that worms are the sole cause of any problem; they could be a factor. Planning for the years ahead will require a combination of keen observation, fact-based information, and trial and error to maintain a healthy garden and landscape. What species might suffer most, and what species should I plant in the future, especially among perennials? While I have found a few recommendations, I have more questions than answers.

Trillium (Trillium spp.) is a native perennial of environmental concern to conservationists. I have never planted trillium, but it grows naturally in nearby woods and is part of the forest ecosystem. This spring ephemeral has shallow roots that include a clumping rhizome. Every year, that rhizome forms new offsets in tightly packed colonies. Keeping in mind that jumping worms typically do not burrow more than a few inches, does the root system of trillium, or its shallow depth, make it more vulnerable? Certainly, the presence of jumping worms in soil supporting trillium will be disturbed, and its rich loamy quality will be compromised. Perhaps trillium is mostly vulnerable, not only because of its shallow roots but because its seed bank is an important component in its reproduction. In optimal conditions, it takes an average of seven years for trillium to develop from seed to flower. Not so long on an evolutionary scale, but slow on a human scale. Being browsed by deer is an added stress factor that jeopardizes this plant.

The lackluster bee balm that grew in my garden last summer also has shallow roots. Instead of a clumping rhizome, however, bee balm has a spreading system of rhizomes and stolons growing just below the surface. Many native perennials in the understory, the kind of environment where jumping worms thrive, have adventitious root systems. Technically speaking, these are not roots at all but underground stems, including rhizomes, corms, and tubers that play a key role in the vegetative reproduction of various plants. Are specific kinds of root systems more susceptible to the jumping worm than others?

In 2022, Annise Dobson, a postdoctoral researcher at the Yale School for Environmental Studies, presented evidence of her observations at a two-day online seminar about jumping worms through the University of Massachusetts Extension. She also belongs to JWORM, Jumping Worm Outreach, Research and Management working group, which is part of the New York Invasive Species Research Institute. Both trout lily (Erythronium americanum) and Jack-in-the-pulpit (Arisaema triphyllum) appear less affected by the worms, according to Dobson.

Like trillium, both these species require rich, moist forest soil replete with lots of leaf litter, yet they do grow deeper than trillium by at least a couple of inches. Both species colonize from a rootstock called a corm. This difference might not be significant in the long haul if jumping worms can persist in an area for years, but it is worth maintaining a studied eye on these species. She also suggested that jumpseed (Antenoron virginianum), blue cohosh (Caulophyllum thalictroides), and Christmas fern (Polystichum acrostichoides) all appeared to be jumping-worm resilient woodland species. Vines are also likely to be more robust, especially those able to grow in disturbed soils.  

Given the assailable nature of shallow-rooted plants, the chief gardening strategy I have encountered to adapt to jumping worm pressure is to grow plants with long roots. Dobson, among others, has recommended cultivating pollinator-friendly prairie gardens. But I am grappling with the implications of "long roots" and how and where I might plant a prairie garden in the woods.

Taproots in mature plants are often long and thick, with lateral roots that develop off the primary root. Several native perennials grow a taproot straight down deep into the soil. Many of these plants are associated with tallgrass prairie ecosystems, that environment being their native habitat.

Often seen alongside big bluestem grass (Andropogon gerardii), the flower of the compass plant (Silphium laciniatum) and its many relatives in the genus Silphium are visible from Amtrak windows as these trains cross Indiana and Illinois. Above ground, the compass plant can reach 12 feet high, but below ground, its thick, woody taproot can make its way to more than 15 feet. Secondary and tertiary roots grow off the main root, and eventually, over its 100-year lifespan, the woody, reddish brown taproot evolves into an extensive fibrous root system. The compass plant resembles a wild sunflower with many yellow composite flowers, about 2 to 4 inches across. It’s a slow grower but has become increasingly popular with landscapers and conservationists, especially with the restoration of old fields and farmland.

Full sun is a prerequisite for a prairie garden, but that is not the case with all prairie plants. Blue wild indigo (Baptisia australis) and blue star (Amsonia spp.) also grow in partial shade. Both have deep taproots, and both are doing well in my garden with about four hours of sunlight per day, although the indigo’s blooms might increase with more sun. It is also in the pea family (Fabaceae) and, as a legume, fixes nitrogen into the soil. Other plants that grow a taproot system include rattlesnake master (Eryngium yuccifolium), wild quinine (Parthenium integrifolium), and butterfly milkweed (Asclepias tuberosa).

Some scientists have informally referred to invasive jumping worms as bioengineers. Like humans, they alter the landscape. There is still so much we have yet to learn about these species. Will chemical or biological controls be developed? Will they suddenly die off inexplicably? Might their presence mean at least some forest will eventually turn into prairie? One takeaway that is evident in both garden and forest environments: seedlings are the most at risk; full-grown plants are less likely to be damaged by jumping worms, but they are not exempt. When a tree falls in my neck of the woods, opening the canopy near my house, I’ll be looking for deep-rooted plants to fill in its place.

For further information on jumping worms, visit Look Out for Jumping Earthworms.