Signal crayfish are crustaceans with long antennae, two front legs with large pincer claws, and eight additional legs used for feeding and walking. They can grow up to seven inches long (tips of claws to tip of tail) and weigh up to 4 ounces, about three-times more than native Minnesota crayfish. Signal crayfish are bluish-brown to reddish-brown in color, with large, smooth claws and a smooth carapace – the protective covering over their head and mid-section. They have a white or pale blue-green patch near their claw hinge, which looks like a signal flag. The undersides of their claws that they display when they are defending themselves are bright red. Young, small crayfish can be difficult for non-specialists to identify.
The signal crayfish is an omnivore, consuming many food sources such as aquatic plants, decaying organic matter, fish eggs, smaller crayfish species and other native invertebrates. They live in a variety of aquatic habitats, from headwater springs and streams to large rivers, lakes and wetlands, and are tolerant of many environmental conditions. They can move across land to find food and suitable habitat. Breeding typically occurs in the fall with females producing up to 400 eggs that they carry throughout the winter. Eggs typically hatch in March to April as the waters warm. Recently hatched crayfish remain attached to the underside of the mother’s tail for a short period until they are able to swim and walk on their own. Their life span is nine or more years.
Origin and spread
The signal crayfish is native to the Columbia River drainage with populations in Washington, Oregon, Idaho, and British Columbia. The species is imported and sold through the pet trade, and to schools by biological supply houses, leading to the potential for illegal release into the wild. It is illegal to import signal crayfish into Minnesota without a permit.
In October 2023, the DNR confirmed the presence of signal crayfish in Lake Winona, near-adjacent to Alexandria in Douglas County. This was the first confirmation of signal crayfish in Minnesota waters.
Don't be fooled by these look-alikes
- Rusty crayfish (invasive)
- Northern clearwater crayfish (native)
- Calico crayfish (native)
- Virile crayfish (native)
Signal crayfish (Pacifastacus leniusculus) is an unlisted nonnative species, which means it is unlawful to release this species into a free-living state in Minnesota. Live signal crayfish may not be imported to Minnesota without a permit.
Threat to Minnesota waters
Invasive species cause recreational, economic, and ecological damage—changing how residents and visitors use and enjoy Minnesota waters.
Signal crayfish impacts:
- Outcompete native crayfishes and other invertebrates for shelter and food.
- Compete with fishes directly for prey and indirectly by consumption of fish eggs.
- Consume and reduce populations of beneficial native aquatic plants.
What you should do
People spread crayfish primarily by illegal release: of aquarium pets, of biological specimens, after improper use and disposal of live bait, and after use in live crayfish boils. It is illegal to release or dispose of unwanted aquatic plants or animals in or near public waters. Refer to Habitattitude for alternatives to release.
Whether or not a lake is listed as infested, Minnesota law requires water recreationists to:
- Clean watercraft of all aquatic plants and prohibited invasive species.
- Drain all water by removing drain plugs and keeping them out during transport.
- Dispose of unwanted bait in the trash.
- Dry docks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body.
There is no known population control for signal crayfish in natural water bodies at this time. Trapping may reduce numbers temporarily, but is not likely to have a significant impact on populations.