It seems that all I am doing lately is talking about invasive pests that threaten our gardens. Several years ago I wrote about a threat to Minnesota gardens — jumping worms. Unfortunately, jumping worms, Amynthus agestis, are back in the gardening news, since their presence has been reported in commercial wood mulch purchased for home use in the Metro area. Not a lot is known about jumping worms but we do know that they are great at digesting cellulose, which is why they can live in and be easily spread in wood mulch. Currently, they have been reported in Scott, Dakota, Hennepin, Ramsey, Anoka, Carver and Washington counties in the Metro area, Otter Tail, Sherburne and Wright counties northwest of the Twin Cities and in Rice, Dodge, Goodhue, Olmstead,Winona, Freeborn, Houston and Fillmore counties in Southeastern Minnesota. There have been 129 reported sightings in Hennepin County.
Jumping worms are an invasive species. What exactly is an invasive species? It is a non-native species introduced and moved in to areas where they are not found naturally by human activity. They cause ecological and economic problems. The threat from jumping worms, also commonly referred to as crazy worms, Alabama jump worms or snake worms, is that they change the soil surface by disrupting the natural decomposition of the leaf litter. They turn good soil into grainy dry worm castings which can look like dry coffee grounds. In the forests they allow the spread of invasive plants by destroying the leaf cover that supports slower growing native plants. In urban gardens they are harmful to turf and ornamental plantings and can kill plants and increase erosion.
All earthworms in Minnesota are invasive; there are no earthworms native to Minnesota. The night crawlers and other worms we are familiar with were introduced to Minnesota by early European settlers. Jumping worms come from East Asia. Another difference is that unlike other earthworms which live as much as 6 feet underground, they live in the leaf litter and the top 1-4 inches of topsoil where they do much more damage to the soil structure. The jumping worm is 1.5 to 8 inches long and brown to grayish black in color. While at first glance it may appear to be an ordinary earthworm it has notable differences. Unlike an earthworm, it has a rigid body that does not produce slime. Most notably it has a cloudy white, smooth clitellum (ring on the body) which encircles the whole body near the head. Other earthworms have a raised wrinkly clitellum. When touched or threatened it behaves more like a snake, slithering and trashing wildly – hence the names ‘snake worm’ or ‘crazy worm.” Sometimes they may even shed their tail in defense.
Jumping worms live for only one season – the adults do not live over the winter. They are parthenogenic, which means they can reproduce on their own, laying eggs in August. The eggs are contained in hardened egg capsules or cocoons and overwinter in the top 1-4 inches of soil. Most eggs hatch in the spring once the temperatures are consistently above 50°, but some eggs stay in the soil and hatch later or even over-winter and hatch the next year. Once they do hatch the emerging worms are 1-3 inches making them difficult to identify.
So how will you know if you have jumping worms in your yard? Look for soil that is dry and grainy looking like coffee grounds. If you encounter them when digging in your garden you will know by their behavior when disturbed. There is also a testing experiment you can do if you want to find out if you have jumping worms in your garden. Mix about 1/3 of a cup of ground mustard seed in to a gallon of water. This is enough solution to test a square foot of soil. Remove any dry soil or leaf litter in the testing area. Slowly pour about half the solution over the soil and allow it to soak in. Jumping worms, which reside in the top few inches of the soil, will start to emerge after one to two minutes. If nothing happens, repeat with the remaining solution just to be sure.
So what do you do if you have jumping worms? Don’t panic. There are no research-proven methods that can control or kill jumping worms, so your best method of management is to remove and destroy them by putting them in the trash. It is illegal to release any worms in Minnesota into the environment, a fact little known by our anglers. Above all avoid spreading them to other sites. Jumping worms can be found in flower beds, mulch, compost, log piles and other places where it is shady and moist. Avoid using mulch from unknown sources and moving mulch from one spot to another. The eggs can be carried in planting and potting soil; if you are moving plants or giving them to others give them as “bare roots.” Thoroughly wash off all soil from the plants. If you are a home composter be sure that your compost pile reaches the proper temperature for complete decomposition. Jumping worms will die when temperatures are over 85° for three days and their eggs will die when temperatures are over 104° for three days. Use only other compost from a reliable source that you know has been composted thoroughly (150°). Make sure you wash off all equipment, tools and shoes that you use in the garden before using them elsewhere.
Lastly, consider spreading the word about jumping worms and report them if you see them. Report them at eddmaps.org/midwest, a website for tracking invasive species in the Midwest. Or you can use the GLEDN (Great Lakes Early Detection Network) app on your smartphone. More info on the app is at apps.bugwood.org/apps/gledn/.