Common Freshwater Jellyfish

C. sowerbii is native to the Yangtze basin in China, but has been introduced on every continent except for Antarctica.

It is usually found in calm, freshwater reservoirs, lakes, impoundments, gravel pits or quarries. It has also been seen in slow-moving backwaters of river systems such as the Allegheny River, Ohio River and Tennessee River in the United States, and the Wang Thong River of Thailand. It is not generally seen in fast flowing streams or rivers.

The medusa's appearance is sporadic and unpredictable from year to year. It is not uncommon for C. sowerbii to appear in a body of water where it had never been documented before, in very large numbers, and its appearance may even be reported on the local news.

C. sowerbii is a predator on zooplankton including daphnia and copepods. Prey is caught with their stinging tentacles. Drifting with its tentacles extended, the jelly waits for suitable prey to touch a tentacle. Once contact has been made, nematocysts on the tentacle fire into the prey, injecting venom which paralyzes the animal, and the tentacle itself coils around the prey. The tentacles then bring the prey into the mouth, where it is released and then digested.

Like saltwater jellyfish, they have stinging cells. However, these cnidocyte cells are used for paralyzing very tiny prey and have not been proven to have the capacity to pierce human skin.

C. sowerbii begins life as a tiny polyp, which lives in colonies attached to underwater vegetation, rocks, or tree stumps, feeding and asexually reproducing during spring and summer. Some of these offspring are the sexually reproducing medusae. Fertilized eggs develop into small ciliated larvae called planulae. The planulae then settle to the bottom and develop into polyps. However, the majority of C. sowerbii populations existing in the United States are either all male or all-female, so there is no sexual reproduction in those populations.

During the cold winter months, polyps contract and enter dormancy as resting bodies called podocysts. It is believed that podocysts are transported by aquatic plants or animals to other bodies of water. Once conditions become favorable, they develop into polyps again.