By Susannah Wood

Last month Norfolk Now published a short piece (“Jumping Worms: Fast-Moving Agents of Destruction”) on the breaking story that Asian jumping worms had arrived on the grounds of the Norfolk Library, adjacent to the new native plant bed. Readers may be wondering what steps can be taken to, at the very least, delay the spread of these insatiable annelids. 

One of the best things to do is to share information and discuss the problem with friends, fellow gardeners, landscape and garden professionals and nurseries, bringing everyone possible on board to control the spread. Nobody set out to loose these creatures upon the town, so there is no need for blame. The biggest threat is to forest ecosystems already under stress from many sources.

Jumping worms first arrived in California about 1870 but have only become problematic in the last 15 years. Why is not well understood. Climate change may be a factor. (Though less voracious, other earthworms in the northeast are nonnative and destructive to forest habitats.)

July is a perfect time to look for jumping worms, as it is when tiny juveniles morph into larger adults. Look for the characteristic flat, pale ring encircling the worm’s whole body near the head, prominent mouth parts and their thrashing movement. Beginning in August, before dying, adults lay eggs in small capsules the size of mustard seeds.

To see if soil, compost or mulch is infested, pick a rainy day when the worms migrate toward the surface. Dig down a bit and check various places. If Asian jumping worms are found, throw them into a bucket of soapy water, then in the trash. 

Alternatively, add one-third cup of ground yellow mustard seed (Asian or Coleman’s hot mustard, not Gulden’s) to a gallon of water. Drench an area one-foot square. Pour half slowly over the ground, wait a few minutes, then pour the rest. While it won’t hurt plants, this solution irritates the worms, making them surface.

The worm population can be reduced this way, but not eliminated. Other strategies that may help include spreading alfalfa pellets or used black tea leaves during the growing season.

If worms are found, don’t share plant material. Also be sure to inform any landscaper or gardener working on the property. Rototilling after May 15 and before May 31 in appropriate areas will kill the juveniles.

There are ways to protect a garden. Request that landscapers or gardeners spray their equipment and tires when coming from another property. Consider paying a little more if they guarantee worm-free materials.

Mulch is one of the most common sources of spread. Yale scientist Annise Dobson recommends obtaining mulch that has traveled “from the tree to the truck,” i.e., that has not sat on the ground where it can be invaded. If that’s not possible, solarizing is fairly simple. The worms and eggs die in temperatures above 105 degrees. Lay a clear plastic sheet, such as painters use, in the sun. Spread an even layer of mulch, six to eight inches deep; cover with another sheet of plastic. Leave an eight-inch border, and fold the top sheet under. Bring the bottom sheet up, lay it on top. Weigh down the edges with stones to keep worms from escaping. Leave for three days. Unfinished compost can also be used as mulch.

Other protective measures include using bare-rooted stock for trees, shrubs and perennials. Closely check any purchased plants. In spring, wash soil off roots and repot in fresh material. In midsummer, unpot and look for “taco meat” castings or use a mustard drench. Avoid community plant sales unless the group affirms the stock is worm-free. Finally, be absolutely sure that any worms purchased for vermiculture or bait are not jumping worms.