Until today I didn’t even know such things existed, but this morning one of the science teachers showed up to work with a jar of water from a local lake containing about four small, live jellies. (I love how every time I’m running out of ideas for a good blog post, the universe provides something awesome!) Getting my camera to take a good photograph of a such a tiny, almost transparent, moving subject proved impossible, so I settled for a short video clip instead.
According to this fact sheet from the USGS, they’re called Craspedacusta sowerbyi and were originally native to China but are now found pretty much throughout the world. However, adult medusae like this (which are only one stage of their complex life cycle) aren’t seen all that often, only in sporadic irruptions. (An irruption is a sudden, sometimes unpredictable increase in population.) It isn’t clear whether they cause any particular problems as an invasive species – they do eat plankton, of course, which could potentially screw with aquatic ecosystems – but they’re harmless to people.
Vilas County, the county in northern Wisconsin where I live, contains more than 1300 natural freshwater lakes, the highest density of lakes found anywhere in the world. That’s literally about one lake for every fifteen people living here. I guess it’s not surprising that with so much freshwater habitat around, we occasionally find weird and surprising things!
[Update: Check out the lengthy comment below by O'fieldstream, who provides a lot more information on these creatures.]