A couple of weeks ago, I told my friend and neighbor Leon Tsomides, an entomologist, that I was getting obsessed with jellyfish, and he told me he once crossed paths with jellyfish — inland.

He was canoeing with his wife, entomologist Kathy Murray, on Eskutassis Pond, south of Lincoln, when he looked down to see “thousands of freshwater jellyfish moving up and down the water column. It was incredible.”

He said they were about an inch in diameter, which accords exactly with descriptions of Craspedacusta sowerbii, the only jellyfish to be seen in fresh water in North America. It’s found in shallow lakes, streams and ponds pretty much worldwide, though it’s native to the Yangtze River valley in China, where it got the name peach blossom fish. It has an extremely adaptable reproductive cycle, and was first reported outside China in water lily tanks in London in 1880, probably having hitched a ride in aquatic plant shipments from China to England.

It was first spotted in North America in Pennsylvania in 1885. It had reached northern New England by the early 1960s, according to Matthew Scott, who wrote me after seeing last month’s Backyard Naturalist column on jellyfish. Matt, a now-retired fishery biologist — and, as it turned out, a colleague and mentor to Leon years ago — wrote up the first report of C. sowerbii in Maine, on Androscoggin Lake, for the periodical Maine Fish and Game in its Spring 1963 issue.

Since then there have been reports like Leon’s of freshwater jellyfish here, much to the wondering eyes of the onlookers. The U.S. Geological Survey lists about 40 reported sightings scattered over most of the state over the past roughly 25 years. But they are seen neither often nor predictably because the medusa form —the white bell with tentacles — does not bloom very often. Conditions, such as food availability and water temperature and alkalinity, have to be just right for it to develop, and when they’re not, which is usually, C. sowerbii lives in its other polyp and podocyst forms, which are difficult to find even for biologists.

Craspedacusta is a Cnidaria phylum jellyfish, meaning one of its characteristics is the typical dangling tentacles with stinging cells (called nematocysts), which are used to capture tiny zooplankton. (Plankton refers to creatures that drift in the water. Zooplankton are animal drifters; phytoplankton are plant drifters. So most medusa-phase jellyfish are actually themselves zooplankton, although usually not tiny.) Unlike some other Cnidarians, C. sowerbii’s sting is not noticeable to humans.

It is noticeable to mosquito larvae, though. And marine biologist Lisa-Ann Gershwin says, thought has been given to using C. sowerbii to control mosquito populations. Good luck with that, she admonishes in her book “Jellyfish: A Natural History,” writing, “Introducing alien species into virgin environments can be problematic, and time and again has proven disastrous the world over.”

Some of the reports I’ve read about C. sowerbii describe it as invasive, but the consensus seems to be that it does not disrupt ecosystems where it has spread after being transported in shipping or perhaps when stuck to migratory birds’ feet.

Few species of freshwater jellyfish are known. Most of them are native to East Asia. In Australia, one other species of freshwater jellyfish in addition to C. sowerbii is known, and several species live in southern Africa. In North America, an invasive freshwater hydroid, Cordylophora caspia, has been identified in 14 states and eastern Canada, but not Maine. The hydroid is the polyp form of the jellyfish. It attaches to substrate in its habitat, and no medusa form of C. caspia has been seen in North America, from what I can tell.

I hope I get surprised someday by a bloom of freshwater jellyfish. Maybe I’ll start taking my grandson, Silas, rowing. He has a knack for finding unexpected creatures.

Dana Wilde lives in Troy. You can contact him at dwilde.naturalist@gmail.com. His book “Winter: Notes and Numina from the Maine Woods” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.

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