Invasive Plant Found in Tilton Pond

August 22, 2023

Last week, we confirmed the presence of an invasive aquatic plant, Utricularia inflata, commonly known as swollen bladderwort, in Tilton Pond in Fayette. This is only the 5th waterbody in Maine known to be infested with this invasive species. One of those is Horseshoe Pond in Chesterville, just six miles from Tilton, although in a different watershed. It was only this year that swollen bladderwort was officially listed as an invasive species in Maine. Because experience with this species in Maine is very limited, we do not yet know what its ultimate impacts will be, or how best to manage it.

A suspicious plant was found in Tilton Pond on August 6th by Bob Capers, a retired professional botanist who is the new Invasive Plant Patrol volunteer coordinator with the Basin-David-Tilton Ponds Association. He identified it as swollen bladderwort, and on August 14th, took a sample to Lake Stewards of Maine. They agreed.

Bob Capers (left) and John McPhedran confirm that the suspicious plant is swollen bladderwort.

30 Mile’s Executive Director, Lidie Robbins, removes swollen bladderwort from Tilton Pond.

On August 16th, two of 30 Mile’s staff (Silas Mohlar and Lidie Robbins), visited Tilton Pond with Bob Capers and John McPhedran from Maine DEP to conduct a survey to determine the size and scope of the infestation. Over the course of three hours, we surveyed most of the pond and found approximately 80 swollen bladderwort plants, which we removed. Because of this number, the invasive has likely been in Tilton Pond longer than this season. Most bladderwort was found towards the northern end of the pond, the end where it flows out to David Pond, but none was observed in the outlet, which is a good sign. It is possible we removed most of what was there, but we did not have time to thoroughly survey the entire pond. 

The upper leaves of swollen bladderwort that form a wagon-wheel shape are inflated to keep the flowering stem above the water’s surface.

With relatively few populations of swollen bladderwort in the state, we don’t know what impact this plant will have. A fact sheet from NH Department of Environmental Services states: “Swollen bladderwort can grow into dense mats over large areas of water. These mats quickly crowd out native plants, limit available light, and consume limited nutrients. Swollen bladderwort primarily reproduces by fragmentation, which means it can easily spread to new locations via a small piece attached to a boat or fishing gear. This also makes it difficult to fully remove manually, as doing so improperly can unintentionally promote the spread of the plant.”

Besides Tilton Pond, many other waters downstream are at risk. From Tilton, water flows down the west branch of the 30 Mile River chain to David, Parker, Taylor, Echo, Lovejoy, Pickerel, Pocasset and Androscoggin. Tilton Pond is one of the smaller ponds in the 30 Mile River Watershed, at just 116 acres. It has a public boat launch.

Bladderworts are carnivorous, free-floating plants (not rooted). They have tiny sack-like bladders used for capturing small prey, such as zooplankton and small insects. Swollen bladderwort looks most like the native Utricularia radiata, commonly known as floating bladderwort. Both species have spoked or wagon wheel-like floats from which yellow flowers arise, but the invasive is much larger than the native. Last week in Tilton, plants were flowering and found near the surface, where they were relatively easy to remove.

Native floating bladderwort (left) next to the much larger invasive swollen bladderwort. Both have wagon wheel-like floats and yellow flowers.

The tiny sack-like bladders catch insects and plankton that are digested for nutrients.

Photo Credit: Josh Robbins (Banner)