ANNAPOLIS, MD (November 1, 2007) - Rusty crayfish, Orconectes rusticus, was discovered lurking in Marsh Creek, a northern tributary to the Monocacy River in Frederick County, by biologists from the Maryland DNR Maryland Biological Stream Survey in June 2007. This is the first state record of this non-native invasive species in Maryland. Follow-up surveys also documented rusty crayfish near the mouth of Conowingo Creek in the lower Susquehanna River, Maryland, in September. Rusty crayfish is infamous for overrunning freshwater streams and lakes. The species can have devastating effects on native crayfishes, aquatic vegetation, fishes, and other stream species. As the most notorious of all invasive crayfishes, the rusty crayfish has been selected as the Maryland Invasive Species Council’s November Invader of the Month.

Rusty crayfish is a large crayfish that can be identified by these features:

• Reddish spots on each side of the body just in front of the tail
• Grayish green color
• Smooth mandibles (mouth parts without serrated edge)
• Black bands on tips of claws

Rusty crayfish is native to the United States – to portions of the Ohio River in Illinois, Kentucky, Ohio, and Tennessee – but it is not native to Maryland. As popular bait for game fishes, this species has been widely introduced outside of its native range. Bait bucket introductions of rusty crayfish have been documented in at least 14 other states and portions of Canada. All of these introductions have spelled disaster for the invaded ecosystems. Rusty crayfish can eliminate native crayfishes and can reduce the quality and quantity of habitat available to other stream species. Rusty crayfish feed heavily on mayflies, stoneflies, and other invertebrates that are important food sources to stream fishes. This species also consumes fish eggs and can destroy aquatic vegetation beds, habits that can impact game fish populations.

The transport of rusty crayfish via bait buckets has spread this species throughout much of southeastern Pennsylvania into tributaries that ultimately enter Maryland, allowing the crayfish to spread south across the Mason Dixon line. Unfortunately, once established, rusty crayfish are very difficult to eradicate from lakes or streams. Their aggressive behavior seems to reduce their vulnerability to population control by fish predators. Efforts to control their populations in invaded lakes of Wisconsin have proven costly and labor-intensive.

It may already be too late to eradicate this species from Maryland waters, but Maryland DNR is aiming to limit its spread. This fall, DNR began a multi-year study to survey the Monocacy River for rusty crayfish. The objectives of this inventory are to determine: 1) the extent to which this species has become established in the mainstem Monocacy River and its tributaries; 2) the potential for population control; and 3) rusty crayfish effects on other native stream species.

Rusty crayfish cannot legally be imported, transported, purchased, possessed live, propagated, sold, or released into Maryland waters. If you find a rusty crayfish, DNR asks that you freeze it, note the exact capture location, and call the DNR invasive species hotline at 1-877-620-8DNR. You can help prevent the further spread of rusty crayfish and other aquatic invasive species. Never release live unused bait, and do not transport live fish or crayfish from one body of water to another.

For more information about other Invasive Species of Concern, visit www.mdinvasives.org or call the Maryland Department of Agriculture at 410-841-5920.

photos available electronically on request.