ORESU-G-06-006
© 2006 Oregon State University
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The New Zealand mudsnail is a threat to our waters. By competing with native invertebrates for food and habitat, it may have a detrimental impact on fish populations, vegetation, and other native biota.
Mudsnails can tolerate a wide range of habitats, including brackish water, and are found living in high densities (often over 400,000 snails/ sq meter) on many different substrates (rock, gravel, sand, and mud).
Spread of the New Zealand mudsnail from 1995 to 2006 in the western U.S. New Zealand mudsnails have recently been found in parts of the Great Lakes region.
The biology, ecology, and distribution rate of the mudsnail suggest that many habitats are suitable for further expansion.
Mudsnail populations in the West are self-reproducing brooders; they clone themselves and retain the embryos inside their shell until they are large enough to release. Also known as parthenogenesis, this reproductive technique means that a single mudsnail can rapidly colonize a new location.
Mudsnails are easily transported to new habitats by field crews because the snails readily attach to or are wedged into the many cracks, crevices, and crannies presented by waders, boot soles, nets, buckets, and so on. New Zealand mudsnails can live for weeks in damp, cool conditions; can easily survive on field gear for long periods of time; and can be transferred to a new environment when that gear is reused.
To prevent the survival of mudsnails on field clothing and equipment, you will need first to clean your field gear and then to treat it, using either the physical or chemical methods listed below. We recommend the following steps:
Physical treatments are recommended over chemical treatments because they
are usually less expensive, more environmentally sound, and possibly less
destructive to gear. However, most physical methods require longer treatment
times and often cannot be performed in the field.
Chemical treatments require a 5-minute soak in a special solution. After
chemical treatment, gear must be rinsed thoroughly with tap water away from
all bodies of water, and all soak solutions and rinse water must be properly
disposed of.
Remember: physical and chemical treatments are not a substitute for physically scrubbing and cleaning your gear.
Physical methods for cleaning gear are effective as well as environmentally sound. Use one of the following methods:
Chemical solutions, at the concentrations below, also kill mudsnails but may not always result in 100% mortality. Gear should be soaked in one of the following solutions for 5 minutes and then rinsed thoroughly with tap water, away from the water body. Store and dispose of solution and used rinse water properly.
These and other chemical treatments are constantly being evaluated.
Treating field gear with chemical methods may result in unintended contamination of the environment. In particular, extreme caution must be taken to avoid contamination of waterways and wetlands. DO NOT rinse your treated gear in a water body.
Treating rubber gear or boots with benzethonium chloride or Formula 409¨ may result in surface cracking of the rubber and loss of water repellency. Chemical methods are not always effective in killing mudsnails. Always scrub your gear and consider using physical methods before resorting to chemical methods.
For more information on the testing of chemical treatment methodology, see R. C. Hosea, and B. Finlayson, 2005, Controlling the Spread of New Zealand Mud Snails on Wading Gear, Administrative Report 2005-02, Rancho Cordova, California: Resources Agency, California Department of Fish and Game.
Size: A mature snail is usually less than 5 mm (.2 in) long. [Omitted graphic: Photo by Jane and Michael Liu.]
Shape: Shell is elongated and dextral (its whorls or spirals lean toward the right). Snail typically has between 5 to 6 whorls on its shell. [Omitted graphic: Photo by D. L. Gustafson, http://www.esg.montana.edu/aim/ mollusca/nzms.]
Color: Most snails have a light-to dark-brown shell that may appear to be black when wet. [Omitted graphic: Photo by Jane and Michael Liu.]
Embryos: Upon dissection, mature snails will have brooded embryos. [Omitted graphic: Photo by D. L. Gustafson, http://www.esg.montana.edu/aim/ mollusca/nzms.]
Operculum: The mudsnail operculum (a rounded plate that seals the mouth of the shell when the animal's body is inside) can be seen on live snails but is not easily visible on dead or preserved snails. [Omitted graphic: Photo by D. L. Gustafson, http:// www.esg.montana.edu/aim/mollusca/nzms.]