Searching for jellyfish can be a fruitless venture, but if you're determined to find one, the best times to go are during the sunny days of August through September. Look for them in the calm bodies of water which they prefer over rocky, fast-flowing rivers.
Jellyfish are usually known to be found in the salty seas, so finding them in Indiana's calm waters is a bit of surprise. Yet Craspedacusta sowerbii - the scientific name for the freshwater jelly - can be found practically all over the world. Besides North Dakota, South Dakota, Montana and Wyoming every state has experienced freshwater jellyfish sightings. But do they really belong here?
Freshwater jellyfish (also known as peach blossom fish) - are considered nonindigenous aquatic species believed to be originally from China. They were first reported in the United States around the early 1900's, with introductions presumably coinciding with the transportation of stocked fish and aquatic plants. They've been spotted - albeit sporadically - in shallow, calm bodies of water ever since.
Why sporadically? Researchers aren't quite sure why the occurrences of these capricious creatures are so unpredictable. In some lakes and rivers, freshwater jellyfish may be present one year, but not the next. Then again, there are some waters that boast them almost every year. Of course, you'll never know if you've spotted one if you don't know what to look for.
It should be known that though Craspedacusta sowerbii is touted as a jellyfish, some argue it is more related to the family Hydra than a "true" jellyfish. Many researchers still call it as such, but others may simply refer Craspedacusta as a jelly. The main difference between Craspedacusta swerbii and "true" jellyfish is the presence of a velum. Its velum is a thin, circular membrane around the cap that helps propel, or move, the jelly forward.
Yet freshwater jellies share many of the same characteristics of jellyfish. They are transparent, gelatinous, umbrella-shaped animals with a whorl of string-like tentacles around the edge of their body. Microscopic barbs called nematocysts run along the tentacles to help capture food and serves as a type of protection against predation. It is this part that stings and causes intense pain to whatever it touches - animal or man. Luckily for us, freshwater jellies are quite small - an adult is the size of a quarter - and there isn't any hard evidence that suggests that they can penetrate through our skin to hurt us the way larger, marine jellyfish could.
Freshwater jellies are part of the phylum Cnidaria - the simplest organisms that have attained a tissue level of organization. Many of the species that make up this phylum go through a multi-stage life cycle that includes two distinct forms: the polyp and the medusa. The medusa form is more familiar and it is at this adult stage where Craspedacusta sexually reproduces. Fertilized eggs that develop into larvae will detach from the jelly and drift away. This form, now called polyps, will also reproduce but asexually, or by dividing from one another (also called budding). The buds will then develop into adult medusa and the cycle repeats.
If you're interested in learning more about this jelly, visit Dr. Terry Peard of Indiana University in Pennsylvania's very informative web site on freshwater jellyfish.