Jumping worms—a Deep Dive
Jumping worms are a group of many species of non-native earthworms. In the Northeast we primarily have three species (Amynthas tokionensis, Amynthas agrestis, and Metaphire hilgendorfri) that are being found by gardeners across Maine. These same species have been identified and studied in in the Great Lakes States. Dr. Lee Frelich was one of the first to identify them in Minnesota in 2006. See this occurence map of the Midwestern States. Recently they have been identified and reported throughout Coastal Maine. Unfortunately, there doesn’t seem to be a single reliable source that is tracking confirmed jumping worm occurrence throughout the US, but iNaturalist reports that jumping worms are widespread across the country.
There are many resources available to help you identify the jumping worms known to our area. Here is a link to the Maine Horticultural Program website that has a lot of good background information that I won’t repeat here. This University of Massachusetts site answers many questions you might have.
While jumping worms are unpleasant in a garden setting, there is no reason to panic; the evidence is that they do not particularly harm garden plants. They do, however, change the texture of the top 2” of the soil. The coarseness of the worm castings near the surface can make it hard for seeds to germinate and seedlings to get started because the organic matter that typically absorbs and stores water has been turned into castings that are loose and dry out quickly. While this could become a problem for vegetable gardeners sowing seeds in shallow rows, it might actually work in favor of reducing weeds.
However, jumping worms are a serious problem for our uncultivated wild areas, especially our woodlands. The flora of our northern forests is already depleted from abundant white-tailed deer and the activities of the non-native European earthworms that have been expanding their range since colonists arrived from with them from Europe. For context about earthworm invasions and their affects watch this video of the talk Dr. Lee Frelich gave for NGBH. Because European earthworms are perennial species, they can move deeper into the soil and remain active throughout the winter. They work to decompose leaves and organic matter in the soil and are valued by some gardeners because they can bring nutrients from deeper in the soil up into the root zone of the plants. The annual jumping worms are active only in the warmer months. Between hatching in the spring and dying in the fall, they work tirelessly to decompose organic matter near the surface of the soil and replace it with their castings.
Sampling
Because jumping worms prefer cool, moist conditions, a good way to sample to see if you have jumping worms present in your soil is to lay a piece of wood on the soil surface. In August, if you have jumping worms, they will be more likely to be found immediately under the wood (a tree cookie is ideal for this). In a recent study, this method was found to be as effective at sampling as the mustard drench method talked about on many websites. The number of worms that hatch and survive each year can be widely variable even in the same garden based on seasonal temperature and rain. Because they are everywhere one year doesn’t mean they will always be abundant.
Lifecycle
Jumping worms start to hatch from their cocoons in March and April in the northeast when the soil temperature around the cocoons reaches about 50 degrees F. The cocoons are about 1/8”–1/4” (4–6 mm) in diameter depending on the species, so emerging juvenile worms are very small and difficult to see. Dr. Nouri-Aiin from the University of Vermont discusses the lifecycle in this talk she gave for NGBH.
Each cocoon typically has one embryo, but about 5% of them contain twins compared with European earthworms which usually have multiple embryos in each cocoon. After hatching, the juvenile worms seek out moist areas with optimal temperature conditions. For example, they will congregate under a tree trunk on the ground when weather is warm and dry. Jumping worms might be more active at night than other earthworms because that is when they can come to the surface and move around in cooler, moist conditions. They are more likely to be found in the garden rather than the lawn.
In early June each species is a different size. The smallest is about 1.5” long and the largest is about 2.5” long. All earthworm juveniles are very hard to tell apart (without genetic analysis), but observing their habitat and movement will help to identify them. Most European earthworms are larger through at least the end of June and already have their clitellum since they are mainly perennial species, so that is another clue. Peak juvenile jumping worm abundance is usually around early to mid-June.
Adult worms are visible the last or third week of July in our area. It could be earlier based on temperature moisture. Once mature, the jumping worms form their clitellum which is the reproductive organ in which cocoons are developed and released. Jumping worms don’t need a mate to produce cocoons. It is likely that jumping worms continue to produce cocoons as long as conditions are good and that one cocoon can be dispersed every 1.5 days through about November. Estimates for the number of cocoons a worm can produce is up to 60 total in its short life. Peak adult abundance is mid-August to early September. The adults die when soil temperatures diminish in the fall. One species can survive about 6 hours at 41 degrees F but not longer than 48 hours.
Control
There doesn’t seem to be a good way to eliminate worms on a large scale. There have not been conclusive results on possible chemical treatments for jumping worms or promising biological controls published yet. Researchers suggest that removing bark mulch or woodchips from the surface of a garden can help to reduce their numbers or potentially even eliminate the worms. Using coconut hull mulch or coir mulch appears to deter the worms. You can use piles of recently removed weeds soaked in water and piles of mulch or compost to attract worms from other areas of the garden where they can be picked out by hand and disposed of.
Jumping worms will die when submerged in a container of water or vinegar or solarized in a plastic bag left in the sun. Once dead, they can be composted because the cocoons inside them are not developed enough to be viable. Another idea is to create a worm home to contain the worms while they live out their lives and then solarize the container in the fall after the adults have died. Dr. Nouri-Aiin reports that all stages of the worms will die at 104 degrees F for a period of 90 minutes. She recommends solarizing for 2 hours just to be safe. This means that garden materials such as mulch or compost you are bringing into or moving around your garden can be solarized to eliminate the potential spread of worms and their cocoons. You should solarize the contents of your worm house at the end of the season if you try that. To do this, spread the soil or compost in layer no deeper than 2” between sheets of plastic (clear or black), folded to prevent escape, in the sun on a hot day. Use a compost thermometer to make sure all parts of the pile reach 104 degrees.
It is always best to reduce the quantity of garden inputs you bring into your garden, but if you need compost, buy it directly from a facility that uses a hot process. Beware of compost stored on the ground. Even with properly made and bagged compost, worms can enter through a tiny hole. It is thought that about 80% of nurseries have worms so this is one way they are being spread around. If in doubt, solarize the bags of compost before using them in the garden.
Managed gardens where we are regularly adding compost are not likely to be affected adversely by jumping worms, but our forested areas are more susceptible to their negative effects. Because the jumping worm castings are on the surface and do not aggregate, they are easily eroded, especially on a slope. Also, a decrease in the amount of leaf litter caused by the hungry worms makes it difficult for forest species, both woody and herbaceous, to germinate and survive, ultimately impacting forest diversity.
While we may never be able to eradicate jumping worms from our gardens, acting responsibly can help to reduce their spread from garden to forested areas. By preventing the spread of worms and their cocoons, we can reduce the risk of them causing increased damage. Follow published recommendations for exchanging plants and practice good garden hygiene with respect to cleaning shoes, tools and equipment when moving between gardens or the garden and natural areas. Educating others about the worms is something we can all do. This is especially important for people who like to fish since they can easily spread the worms to natural areas when disposing of unused bait.
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