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Alligatorweed
(Alternanthera philoxeroides)
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Rusty Crayfish
Photo credit: U.S. Geological Survey, Bugwood.org
(Orconectes rusticus)
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Species at a Glance
The rusty crayfish is a large, aggressive crustacean that can outcompete native crayfish for food and shelter, and devastate aquatic ecosystems with its huge appetite.
Identification
The adult rusty crayfish is typically 8-13 cm (3-5 in) long, with large, black-tipped claws and smooth mouthparts. It is typically grayish-green to reddish-brown in color, with a set of dark rusty orange spots on each side of the carapace; which is its most distinguishing feature. Due to the hybridization of male rusty crayfish with female native crayfish, these spots may not always be present or well developed.
Similar Species
May be confused with other native and invasive crayfish, including the calico crayfish (Orconectes immunis), virile crayfish (O.virilis), and northern clearwater crayfish (O. propinquus). However, these crayfish generally have smaller claws and lack the rusty orange spots present on the carapace.
Habitat
The rusty crayfish is often found in silt, clay, or gravel substrates, and prefers areas with adequate rock, log, and debris cover; however, it can survive in a variety of habitats, including lakes, rivers, ponds, and streams. It is most active at temperatures above 8° C (46°F).
Spread
Anglers using the rusty crayfish as bait is one of the most common ways it has spread to new regions. It is not necessary to have both males and females to establish a new invasion; a female carrying viable sperm could begin a new population if released into a suitable environment.
Distribution
While its native range extends throughout the Ohio River basin in Ohio, Kentucky, Indiana, and parts of Tennessee and Indiana, the rusty crayfish has spread beyond this range to become invasive in other areas of the United States. In the Mid-Atlantic region, the rusty crayfish has established in all Mid-Atlantic states except for Delaware.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Environmental Impacts
The rusty crayfish reduces native crayfish populations by competing for food and daytime hiding locations. It is a very aggressive and voracious eater, destroying aquatic plant beds and reducing food, shelter, and spawning sites for other organisms, including valued sport fish.
Videos
Note
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).