Land of the Rising Worm
Jumping worms have spread from Japan and become an invasive species in North America. As we learn how to fight them, what can we learn from their homeland?
They’re frighteningly strong, and have multiple ways of deterring potential predators. They can chew through plants extremely quickly, and even change the texture of the soil beneath them to render it inhospitable for new growth. They can devastate local ecosystems if left unchecked — and as they begin to establish themselves as an invasive species in North America, that possibility becomes all the more threatening.
A characterization like that might evoke an image of a large, terrifying beast, but it actually describes a lowly worm — or rather, three types of worm. Amynthas agrestis, Amynthas tokioensis, and Metaphire hilgendorfi have collectively become known as the “Asian jumping worm” in the United States and Canada. I’ve written in more detail about why they’re considered to be such a dangerous ecological threat in a separate article.
But even beyond that, their name raises another question entirely: if they’re from Asia, then what parts of it specifically? And do they struggle with these species in the same way that North America is starting to?
Even without looking anything up, there’s one giant hint to where these worms come from: “tokioensis”, the second part of one species’ taxonomical name. If that reminds you of Tokyo, Japan, then you’re right on the money. All three types of jumping worm can be found just about everywhere in Japan — save for the upper half of Hokkaido, the country’s northernmost island. They can also be found in disparate spots in nearby South Korea, though not nearly to the same extent.
But of course, these countries are far from being epicenters of environmental collapse. So how do they weather the storm these worms seem to threaten? What part of the local ecology makes it so they don’t thrive the same way they’ve started to here?
Because jumping worms are exponentially more prevalent in Japan, I investigated resources in Japanese rather than in Korean. I can speak and read a bit of the language, but I’m unfortunately not fluent, so keep in mind I’m primarily using Google Translate rather than navigating these pages in their original language. I’ve done my best to scout for mistranslations, but I can’t guarantee 100% accuracy, as much as I’d like to.
To start, here are the Japanese names for each of the three big species of jumping worm:
- Amynthas agrestis: Hatake-mimizu (ハタケミミズ)
- Amynthas tokioensis: Fukisoku-mimizu (フキソクミミズ)
- Metaphire hilgendorfi: Hitotsumon-mimizu (ヒトツモンミミズ)
Because we don’t have different common names for these species in English, I’ll be using these Japanese names to distinguish them here. You’ll see me refer to them as the Hatake jumping worm, Fukisoku jumping worm, and Hitotsumon jumping worm, respectively.
But with that disclaimer out of the way, we can start scouring the Japanese internet for information. And as it turns out, we don’t actually have to look for very long, since it has a prominent, comprehensive worm encyclopedia that’s completely free to access: Japanese Mimizu. It’s how I found the Japanese names for each of those three species from their taxonomical names, and it also includes a great deal of information on what they look like, where they live, and how they fit into their local environments — citations and all.
Japanese Mimizu has separate pages for all three of the aforementioned species, with different pieces of information on each. But looking at the details present on each page, there are some clear patterns which reveal themselves, and which can tell those of us who live overseas what we should look out for:
A distinct size and appearance
- All three species have a wide range of potential lengths, but Fukisoku is generally the smallest (6.5 to 14.5 cm), Hitotsumon is the largest (8.5 to 27 cm), and Hatake is in between (7 to 20 cm). For comparison, Lumbricus terrestris, one of the most common earthworms in the US, ranges from 9 to 30 cm. Though it isn’t always the case, jumping worms tend to be on the smaller side.
- Rather, you might consider looking closely at the number of segments these worms have. These three species of jumping worm all tend to have anywhere from 70 to 110 segments. But Lumbricus terrestris has far more, ranging from 110 to 180.
- Color can be another identifying factor. Jumping worms tend to have the same reddish-brown bodies and stark, pale orange-gray or red-gray rings that we’re used to seeing on our own earthworms. However, there are two main differences. First, the ring is often pushed closer to the head on jumping worms than it is on their counterparts, and it doesn’t extend outwards or form a “bump” on the worm’s body. And second, there’s no major color difference before or after the ring, whereas a European worm is more likely to have one section be much darker than the other.
Cluttered homes
- These worms — like most — love living in places with tons of decaying organic matter. They can make themselves at home in a wide variety of locations: forest floors, garbage piles, riverbanks, even sawmills.
- Farmers in particular need to stay wary, since they’re known to take up residence in agricultural areas like greenhouses, flower beds, and no-till growing plots. Note that tilled plots won’t generally have these worms, but they’re also far less hospitable for worms as a whole — as well as mycorrhizal fungi and other species which can keep soil healthy.
A love of the Southern heat
- Japan and the northeastern US have quite similar climates, but the southern US is much hotter year-round. That means all of these worms can hatch earlier and live longer in the South.
- In both their natural habitat and the American Northeast, jumping worms generally hatch around early May, reach maturity around July, and die around November. But in the South, they generally hatch in April, mature sooner in the summer, and can survive even as late as December.
Kids in camouflage
- It’s tempting to stop these worms’ spread before they even hatch — but that’s also when they’re the hardest to detect.
- Their eggs are often buried slightly below the ground surface, and they’re quite small and difficult to see. Hitotsumon’s are described as “blackish sepia color” — not exactly conspicuous when they’re surrounded by clumps of soil that are the same size and shape as them.
But there’s one detail that seems to be missing from Japanese Mimizu: how to stop jumping worms’ spread.
To an American, it can be strange to find no information on how to curb the population of an invasive species. But for a resource from Japan, it might be stranger to include it at all; after all, for them, these are regular, native species that their local environment has had much, much more time to adapt to and evolve around.
Speaking of local adaptations, there’s one major factor which prevents jumping worms from being an issue on their home turf: nutrition. They can live in a lot of different places, but outside of any human influence, they mostly reside in forests, feasting on rotting wood, fallen leaves, and other decaying plant matter. But the trees that make up Japanese forests — including the Japanese red pine, evergreen oak, zelkova, ginkgo, and Hinoki cypress — are vastly different from their American counterparts; many don’t appear to provide as many nutrients to the species that feed on them. That can make these worms much healthier, more resilient, more numerous, and harder to stomp out in the States than they are overseas. And when combined with their elongated lifespan by way of the Southern heat, the prospect of them spreading becomes even more frightening.
If you’re interested in learning ways you can help combat the rising tide of jumping worms in the US and Canada, I’ve written about it in a separate article here. But even if you’re lucky enough to not have them on your doorstep, knowing how to identify them is a vital skill all its own — and one which is made far easier with resources from their native range.
