Making occasional surprise a
ppearances to the delight of swimmers in Michigan’s inland lakes for well over eighty years, freshwater jellyfish are an exotic, though non-invasive species that were accidentally imported from China in the early part of the twentieth century. A recent appearance of the usually penny-sized undulating medusa in Diamond Lake in Newaygo County received a surprising amount of attention from various news media outlets throughout Michigan in recent weeks. Freshwater jellyfish (scientific name: Craspedacusta sowerbyi), found throughout the much of the world, including forty four of the United States, sometimes appear in northern temperate inland lakes in large numbers in late summer when water temperatures and other ecological conditions are just right. One quarter of an inch to one inch in approximate size, freshwater jellyfish are amazingly translucent and bell shaped in appearance, and possess 50-500 short and long tentacles that are utilized by the species for feeding, stability, and mobility. Preferring relatively calm waters that allows them to feed on tiny zooplankton, freshwater jellyfish rarely appear in the moving waters of rivers or streams. Capable of asexual reproduction, freshwater jellyfish larvae attached to hard substrate are capable of remaining dormant for a long period of time, and emerging only when ecological conditions are conducive to their growth and survival. Swimmers should be aware that freshwater jellyfish pose no danger to humans, and present no threat to the ecology of our inland lakes. Highly unpredictable and relatively rare appearances of the exotic freshwater medusa in our inland lakes should be considered cause for delight!