Thanks for the question.

The most immediate thing you should do is to be sure you have jumping worms. Their most characteristic feature is a circular white band near their anterior end. Regular earthworms do not have this white band but a more reddish band. This structure is called the clitellum. See:

https://extension.umn.edu/identify-invasive-species/jumping-worms - :~:text=Jumping worms live in the,disposed of in the garbage.

https://mitppc.umn.edu/research/research-projects/jumping-worms-minnesota

If you do have jumping worms, they do eat plant roots. Whether they in fact are responsible for the decline in your hostas is an open question as other organisms (e.g., voles) can also feed on plant roots. See:

https://blog-fruit-vegetable-ipm.extension.umn.edu/2021/03/jumping-worms-what-do-farmers-need-to.html - :~:text=Jumping worms have also been,worms might impact vegetable crops.

Unfortunately, there are no satisfactory ways to selectively eliminate jumping worms. One recourse is to completely replace the upper six inches of existing dirt with dirt having no jumping worms. Obviously if you have a large garden/area, this may not be a feasible recourse. The one bright thing about them is that adults only live for one year. Here are some of my additional thoughts that may or may not be applicable for your situation and conditions:

1). Try to prevent the spread of jumping worms to other areas. Avoid moving soil or plants that may contain their cocoons, which look like small, shiny, lemon-shaped objects. Cleaning gardening tools, shoes, and equipment can help prevent their spread.

2). Hand-picking the worms can be effective for small infestations. Wear gloves while doing this to avoid skin irritation and wash your hands thoroughly afterward. Place the worms in a sealed plastic bag and dispose of them in the trash.

3). You can create physical barriers to prevent the spread of jumping worms. This involves digging a trench lined with a barrier material, such as plastic or metal, to block their movement into a specific area. You may want to think of this for your hostas.

4). Applying a thick layer of mulch can help deter jumping worms, as they prefer loose soil. Mulch can make it difficult for them to burrow and move around.

5). Consider planting native plants in your garden. Jumping worms are known to prefer non-native plant species, so promoting native plant diversity may deter them.

The following will provide you additional information on these and related points:

https://www.youtube.com/watch?v=ke1fQ7Fyaw0

https://extension.umd.edu/resource/invasive-jumping-worms

https://www.milorganite.com/blog/garden-landscape/managing-worms-your-lawn

https://www.invasivespeciescentre.ca/jumping-worms-in-the-garden-what-you-can-do-to-help/

I wish I could be more optimistic, but these are the realities regarding this critter. Good Luck. Please get back to us with any additional, related questions.