The rusty crayfish is a medium-to-large freshwater crayfish with a mottled brown-green body and a distinctive rust-colored spot on each side of the carapace, just behind the claws. These spots are the species’ most reliable field mark, though they can vary in intensity.
The claws are robust and smooth, often with dark tips and a gray-green to olive tone. Compared to many native crayfish, the claws appear oversized and confident—an impression reinforced by the animal’s aggressive posture.
Color ranges from olive-brown to reddish-brown, often blending seamlessly with rocky streambeds. Freshly molted individuals can appear lighter or slightly translucent.
Rusty crayfish have spread widely through bait-bucket releases and accidental transport. In many regions they are now considered invasive ecosystem engineers.
They tolerate a wide range of temperatures and water conditions, giving them a competitive edge over native crayfish.
Omnivorous and highly opportunistic:
This broad diet contributes directly to their ecological impact.
Rusty crayfish are unusually aggressive. They outcompete native crayfish for shelter and food, often displacing them entirely. Their feeding behavior can strip aquatic vegetation, altering fish habitat and increasing erosion.
They are most active at night but can be encountered during daylight, especially in clear, shallow water.
In many states, regulations prohibit transporting live rusty crayfish to prevent further spread.
Rusty crayfish are a textbook example of how a single introduced species can reconfigure entire freshwater systems. Their success is not due to fragility or specialization, but to adaptability, aggression, and tolerance—traits that reward them in human-altered environments.
They are frequently photographed during stream surveys because they do not retreat quickly, often raising claws instead.