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A small freshwater jellyfish swims around a jar as science museum visitors look on.
I have to admit that at first we thought it was a joke. We heard that a Science Museum volunteer had brought in a "freshwater jellyfish" to the Collector's Corner. We were even momentarily fooled when we looked at the jar full of water because it looked empty. However, as we peered closer we saw three amazing creatures about the size of a quarter bobbing around in a jar of Minnesota lake water.
Science Museum volunteer Will Hirsch and his neighbor Tim McDonough found these unique creatures in Lake Jane near the city of Lake Elmo, MN. What they found was the subject of a question to the Minnesota Department of Natural Resources a couple years ago:
In August 2003 I was fishing on a Minnesota-Ontario border lake and noticed hundreds of round, translucent discs about the size of a quarter rising to the surface. The discs had an irregular bluish central pattern and were soft, flexible, and slimy. What were they?Jim Collinge
You likely were looking at freshwater jellyfish (Craspedacusta sowerbii), says DNR research scientist Gary Montz. These little animals grow attached to under-water surfaces for part of their lives, then form buds that turn into the floating form, called a medusa. Freshwater jellyfish can appear in large numbers in lakes during late summer. Like ocean jellyfish, they capture their food-mainly zooplankton-with stinging -tentacles. Unlike ocean jellyfish, they cannot sting or harm you.
So what Will and Tim had discovered was the medusa form of a Craspedacusta sowerbii. These little creatures have been reported in Minnesota and almost every other state in the continental US. These animals like still waters, so they won't be found in rivers or streams. As they float around they passively feed on even tinier animals that are found in almost all lakes called zooplankton. They are easiest to spot in August and September, so keep an eye out for them next time you go swimming or fishing at your local lake.
How do they reproduce? How did they get here? What kind of water do they live in? Researchers at the Indiana University of Pennsylvania, Japan, and Australia are all studying these strange creatures to come up with answers to these questions.
Have you seen a jellyfish in any of Minnesota's lakes?