• Natural History of the the freshwater jellyfish.

• When would I see freshwater jellyfish?

• What do freshwater jellyfish eat?

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• Where do freshwater jellyfish live?

A tiny, stalked form of the jellyfish (the polyp) lives as colonies attached to stable underwater surfaces such as rooted plants, rocks, or tree stumps.  The microscopic polyp colonies feed and reproduce during the spring and summer months.  The polyps reproduce asexually.  Some of their offspring are the jellyfish that can be seen at the surface.  The "jellyfish" or medusa reproduce sexually. Fertilized eggs develop into planula larvae which eventually settle to the bottom of the pond or lake and develop into polyps.  However, in the United States, most populations of jellyfish are either all male or all female, so sexual reproduction may be rare.

The appearance of the jellyfish is described as sporadic and unpredictable.  Often, jellyfish will appear in a body of water in large numbers even though they were never reported there before.  The following year they may be absent and may not reappear until several years later.  It is also possible for the jellyfish to appear once and never appear in that body of water again.

During the winter, the polyps contract and become "resting bodies" that are capable of surviving the cold temperatures. Some scientists believe that the resting bodies, called podocysts, are one way in which the jellyfish are transported from lake to lake. It is believed that the podocysts may be transported on aquatic plants, by aquatic animals, or perhaps on the feet of birds. When conditions become favorable, the podocysts develop into polyps, and the life cycle is continued.

Usually late summer.  August and September are peak months for jellyfish sightings in Pennsylvania when lake water is warm and food is abundant.  The jellyfish will be floating or swimming gently just below the surface of the water.  They are easily seen by the naked eye.  They often surface in large numbers called "blooms".   Sunny days are especially good for spotting jellyfish.

C. sowerbii jellyfish eat tiny, microscopic animals called zooplankton that are found suspended throughout the water.

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C. sowerbii jellyfish are most often found in calm, freshwater lakes, reservoirs, man-made impoundments, and water-filled gravel pits or quarries.  They can also be found in recreational fishing and boating areas.  They have been seen in large river systems such as the Allegheny River, the Ohio River, and the Tennessee River.  The jellyfish prefer standing water rather than currents.  So, they generally are not seen in fast flowing streams or rivers.

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