This summer, the hot days have made me explore a number of waterways for new access points and new destinations. With new territory come new hazards.
One plant that came to my attention is Arrow-leaf Tear Thumb — referring to its ability to scratch your skin. This small, Polygonum sagittatum is a member of the buckwheat family that’s native to our wetlands. What is immediately apparent about Arrow-leaf Tear Thumb is that the stems are completely covered with tiny barbs that feel very sharp against bare skin when you brush up against them. Luckily, they feel almost smooth when you run your fingers down the stem.
The plants I found this week were about 4 feet high. Instead of using tendrils that spiral around other plants, they use their tiny barbs to climb the stems of the tall grasses and rushes that surround them. With very small stems and only a few leaves, Tear Thumb doesn’t have much weight to hoist as it competes for sunlight. The small, white flowers of these little annual plants grow in a compact cluster at the end of the stem.
One extensive mass of Tear Thumb made my first unaware steps feel like an attack by thousands of tiny stinging insects. It was completely impassable for the small children in shorts with whom I was adventuring. Although the sting-and-itch combination only lasted a moment, it was a deal-breaker for access to the water.
The sandaled children and I easily backed away from the Tear Thumb, but there was another assault on two children this summer by an organism that wasn’t so easy to dispatch — swimmer’s itch. I know of three cases of this uncomfortable, itchy rash.
Swimmer’s itch, or cercarial dermatitis, is also known as duck itch. It appears when small parasites that usually live in freshwater snails come in contact with human skin. The microscopic larvae of the parasite leave the snails and float freely in fresh water in search of ducks, geese or gulls as secondary hosts. When the larvae come in contact with humans, they burrow into the skin. Because humans can’t host them, they die almost immediately, but the places where they’ve burrowed react with a local rash. The Center for Disease Control’s website reassures that it is not contagious and resolves on its own in a few days. Over-the-counter antihistamines and itch remedies can help with the discomfort.
The parasites that cause swimmer’s itch concentrate in water that is shallow, warm and slow-moving. Children are most at risk because those conditions also describe their preferred play areas. By avoiding areas where there are obvious waterfowl populations or by choosing cold, moving water bodies for swimming, you can avoid contact. Fishermen, boaters and paddlers are advised to wear waders or even socks to protect your ankles when launching from shallow, warm shorelines where the water doesn’t move much and there are ducks or geese. The floating parasites can’t penetrate clothes. A thorough toweling after coming out can remove them before they burrow into the skin.
Infected snails continue to produce larvae for the remainder of their lives, but the larvae only live about 24 hours and can’t develop without an appropriate secondary host. Swimmer’s itch is not a new problem from an invasive species. However unwelcome, the snails and the parasites are part of our local ecosystem.
If you do get swimmer’s itch, consider reporting the locations where you swim to the local health department. If a number of cases occur, health officials and lake monitors will want to trace the source.
Elizabeth Lee is a licensed guide who lives in Westport. She leads recreational and educational programs focused in the Champlain Valley throughout the year. Contact her at email@example.com.