Since at least 2013, non-native invasive jumping worms (Amynthas species) have populated several Arboretum forests. Jumping worms alter forests by quickly consuming large amounts of leaf litter. Similarly, jumping worms have been found in gardens, lawns, and forests throughout Wisconsin and across North America. Jumping worms may affect garden plant health, though researchers are still studying specific changes.

With the arrival of spring, local gardeners may start to notice more worms, especially as they grow throughout the summer. As an annual species, jumping worms usually hatch in April and May throughout south central Wisconsin, and they die in winter of the same year. Jumping worm eggs, called cocoons, overwinter in the soil, hatching in spring to begin the cycle again.

Last summer, Dane County experienced widespread severe to extreme drought conditions. During this period, the jumping worm population sharply declined. However, like many plants that create seedbanks, jumping worms create a cocoon bank – a buildup of cocoons laid each year. Cocoons are drought-tolerant and cold-hardy, meaning they can survive a wide range of conditions. At the end of 2023, we wondered what the jumping worm population would look like in 2024.

Prior to the drought, Arboretum researchers began a project to study how jumping worms grow throughout the year. Researchers surveyed a site in Gallistel Woods twice a month to count and measure every jumping worm. This project documents individual worms and population growth throughout the year and helps us track how the population responds over time to disturbances like drought and long-term climate change. This information can also be used to help develop and test control measures.

In late April, Arboretum researchers began surveying for 2024. Despite the drought-related population decline in 2023, the first two surveys found more jumping worms this year than there were at the same time last year. In the second survey week, specifically, there were almost three times as many jumping worms. This noticeable difference may be related to a wetter and warmer spring creating more hospitable soil conditions for cocoon hatching. It’s also possible that last year’s dry conditions kept newly laid cocoons from hatching, and those cocoons instead overwintered and are hatching this spring. Researchers will keep monitoring the population through the end of the jumping worm life cycle.

Gardeners in the area may also find a lot of jumping worms, but it remains to be seen how populations will differ across properties and change through the year. Weather conditions, as well as site conditions, may affect jumping worm population levels.

For more information about jumping worms, visit the Wisconsin Department of Natural Resources jumping worms topic page.

—Danielle Tanzer, data and GIS coordinator