Push a hand into the top inch of ground under a maple.
It should come up cool and matted, roots and half rotted leaves knitted into something that holds its shape.
In an infested yard it comes up loose. The texture is coffee grounds, dry and granular, and it runs off the fingers like cereal.
Underneath is bare mineral dirt. Above it, almost nothing left to rot.
The layer that took a decade to build is simply gone, and the animal that ate it will not be there in April.
Why this worm does not work like the one in a bait cup
A nightcrawler burrows.
It drags leaves down a permanent vertical shaft and works them into the mineral layer, mixing as it goes, which is the behavior every gardening book means when it calls worms good for soil.
These feed at the surface instead.
They stay in the litter, shred it where it lies, and leave behind loose castings with no crumb structure to hold water or seedling roots.
They are also quick. Two generations in one season have been recorded in Wisconsin and in Maine, where a single annual cycle was long assumed.
And they do not need a mate. Reproduction is parthenogenetic, so one animal riding in a pot of nursery stock is an entire population.
The object that does the actual invading
The adults are not the thing to plan around.
Every one of them is finished by the first hard frost, and nothing at all overwinters as a worm.
What overwinters is a cocoon about the size of a mustard seed, dark, irregular, and hard to tell from a grain of grit.
It sits in the top few inches of soil, which is exactly the depth a trowel moves.
So it travels in a pot of perennials, in bagged mulch, in the tread of a boot, and nobody stops it, because at that size there is nothing to stop.
An infestation that shows up in July was usually carried home the previous autumn by somebody being helpful.
What the counts and the heat trials found
The litter number is the one worth memorizing. In Wisconsin forest plots, leaf litter fell by roughly 95 percent where these worms had established, and nutrient turnover ran about twice as fast.
Researchers describe the result as a fast release fertilizer, which sounds generous until you remember that a forest floor is a slow release system on purpose.
On heat, the figures separate cleanly.
Adults are finished by three days at 85 degrees. Cocoons are tougher, and work out of a Wisconsin arboretum puts the threshold at three days at 104 degrees.
Commercial composting runs hotter than that, near 131 degrees, which is why finished commercial compost is considered safe and a backyard pile often is not.
One widely shared figure, 104 degrees for two hours, is an outlier and should not be relied on.
Two treatments that sounded plausible did nothing measurable in trials. Biochar failed. Diatomaceous earth failed. There is no registered pesticide for any of this.
The number in most coverage that traces to nothing
You will read that jumping worms are in 35 states.
That figure has no source anybody can point to. The regional pest center that tracks the spread puts it at 38 states, and even that overstates the picture, because distribution inside a state is patchy rather than general.
One county can be thick with them while the next has none.
Minnesota made possession and transport unlawful effective in the summer of 2024, and the reasoning behind that rule sits in the same litter research the federal foresters summarize.
Here is the part that gets left out. Nobody has documented reversing an established infestation anywhere, by any method, and state guidance is written around containment rather than removal, as the state rules make clear.
The honest caveat runs the other way too. A 2020 study found the effects depend on which trees are overhead and are not uniformly bad, and one long running site has not yet shown a strong change in understory plants, the kind of slow signal that also shapes arguments about pollinators and about what actually lives on a forest floor.
What is left to do in your own yard
Check what arrives before it goes in the ground, because almost every new infestation is delivered rather than grown.
A mustard pour will bring anything in the top few inches to the surface in minutes, which makes a pot easy to screen.
Keep soil, mulch and divided plants from moving between properties.
Clear sheeting over bare ground through high summer holds the top inches above the cocoon threshold, which is the one control with evidence behind it.
None of that is a fix.
The useful reframing is that the adults writhing in the mulch are the visible half of the problem and the half that solves itself every autumn, while the half that decides next year is a scatter of grit sized objects nobody has ever been able to count or find.
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