Department of Natural Resources
zebra mussel Dreissena polymorpha
mussel has a small, triangular shell with alternating light and dark
bands. It grows to one and one-half inches in length. The inside of the
shell is white.
mussel may be found in Lake Michigan and the Ohio, Illinois and Mississippi
rivers in Illinois. It attaches to nearly any hard, underwater surface
by gluelike fibers called byssal threads. Areas with large numbers of
these animals may have 30,000 to 70,000 zebra mussels per square meter.
Zebra mussels attach to water intake pipes of power plants and water treatment
plants. Millions of dollars are spent each year for cleanup and repair
to these structures. Zebra mussels also attach to other mollusks, which
may stop the native species from feeding or reproducing. The zebra mussel
reproduces at an age of about one year. Each female may produce 30,000
to 1 million eggs per year. Breeding occurs from May through October.
Males and females release eggs and sperm into the water. Fertilized eggs
develop quickly into free-swimming larvae called veligers. Veligers form
shells and, after about 10-15 days, settle on the bottom and attach to
anything hard. Zebra mussels filter water to remove plankton for food.
They are often found attached on native mussels near the incurrent siphon,
the place where food is taken into the shell. Each zebra mussel may filter
up to one liter of water per day. Filtering improves water clarity but
reduces the amount of plankton available for native species. The zebra
mussel is native to the Caspian Sea region of Asia. Zebra mussels were
brought to the Great Lakes from Europe in the ballast water of ships in
1986. They may be spread by livewells, bilge water, boats and boating
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