Your friendly neighborhood Freshwater Biologist here with a special report on pond snails.
Aquatic snails are generally fantastic. These members of the Mollusk family serve the ecosystem near the bottom of the food chain, consuming organic material (plant matter mostly) and going about their business (slowly….cuz they’re snails) of making more snails. The species that live in the Midwest are mostly small (about the size of your thumbnail) and truck around down in the rocks and sediments looking for stuff to eat.
Aquatic snails are an abundant food source for a multitude of organisms, providing a great source of energy for the critters that prey upon them. There are some invasive species trying to wiggle into their niche (I’m looking at you, zebra mussels), but as a whole, the pond snails are in good shape population-wise.
Now, the dark side of pond snails……..
There is a creature in our midst that is the bane of lounging aquatic humans just about everywhere. Swimmer’s itch. This vile organism causes sizable purple welts that produce an unholy itch the rival of which I have not encountered in this life. I believe the correct term is an inflammatory immune reaction. These welts last more than a week (about a month in my case), and are generally the worst….just the worst!
What’s this have to do with pond snails?
Well, snails are an intermediate host for the little parasitic bast…..uh… critters. Swimmer’s itch is a flatworm that needs an aquatic snail as a host for a portion of its lifecycle. It encounters humans when it’s looking for its final host, a duck.
The incidence of swimmer’s itch increases as the pond snail population increases. Therefore, if you see many snails in your pond or lakeshore, it is likely that swimmer’s itch resides there too. I find that occurs in highly organic sediments most frequently. So, wherever there is organic soft sediment (muck), beware.
Here is the lifecycle of swimmer’s itch as provided by the CDC.
What do you do if you know you have swimmer’s itch in your waterbody? One thing is to reduce the number of snails in your area. That is, reduce their available habitat and food sources. I recommend two strategies to reduce muck in order to revitalize your shoreline habitat and reduce the rearing areas for swimmer’s itch.
I recommend beneficial bacteria products that eat away at the goo, greatly reducing the total volume of sediment and improving near shore habitat.
Here are a few products that I like:
Kasco Macrozyme Bacteria.
Scott Muck digester
Another way to remove the muck that the snails live in is to physically remove it from the premises. The easiest way to accomplish this is with a watermover. Installing a watermover at the end of your dock or pier will greatly reduce the organic soft sediment, improve fish habitat, and clear any floating debris from around your shoreline.
The best units I’ve found are these:
Scott Aquasweep (also available with an oscillator for even better results)
Another means of managing swimmer’s itch is to kill it off. This will only work in small areas as it is not feasible to treat large lakes.
This is a last resort option. The products that are effective will have to be used at maximum label dosages and have other deleterious effects to the ecosystem. There are no products labeled for use against the organism responsible for swimmer’s itch. There are, however, algaecides that are effective in killing the organism. The active ingredient (copper sulfate penthydrate) is lethal to many small organisms (bacteria, algae, many others) and it can also kill the larval stage of our favorite flatworm.
NOTE: This is a non-label use of an aquatic pesticide. You should follow all of your local laws and ordinances when applying it to mitigate any downstream effects. I recommend hiring a certified applicator to help you apply this product. The brand I use is called Earthtec.
Anyhoo, I hope I have helped you understand this particular scourge a little better. Thanks again for taking the time to read my articles. If you have any questions or comments, please feel free to comment or contact me through Midwestponds.com.