What are they?
A mitten crab is light brown to green in color, with brown hairy patches resembling mittens on its claws. It spends most of its life in freshwater, but reproduces in saltwater. A mitten crab can prey on and compete with many native aquatic species, posing a threat to ecosystems and fisheries. It is native to Asia.
Are they here yet?
No. Mitten crabs have been reported, but not confirmed, in the Pacific Northwest. They are in San Francisco Bay and upstream of the bay.
Why should I care?
This crab may pose a serious threat to ecosystems and fisheries along the West Coast. It can prey on and compete with many native aquatic species, including clams, mussels, and the eggs of fishes. Its burrowing can damage levees and riverbanks, and lead to clogging of fish screens and pipes, hampering water delivery. It may carry lung flukes, which can infect humans, particularly when a crab is eaten uncooked as a delicacy. Mitten crabs have been known to steal bait off hooks and damage fishing nets.
What should I do if I find one?Report a sighting
How can we stop them?
Report sightings of mitten crabs, and put caught mitten crabs on ice. Mitten crab is classified as a Prohibited Aquatic Animal Species in Washington, meaning it may not be possessed, purchased, sold, propagated, transported, or released into state waters (Revised Code of Washington 77.12.020, Washington Administrative Code 220-12-090). The importation of mitten crabs is regulated further by the federal Lacey Act, under which they are listed as Injurious Wildlife Species.
What are their characteristics?
- Brown hairy patches resembling mittens on white-tipped, equal-sized claws.
- Light brown to green in color, with a deep notch between the eyes.
- The carapace, or top shell, measures up to 3 inches with four prominent spines on either side, and legs are typically twice as long as the carapace is wide.
- Juvenile's claws may not be hairy if the carapace is less than 1 inch wide.
How do I distinguish them from native species?
A crab observed in freshwater is most likely a mitten crab.