About the Chinese mitten crab
This crab is not a picky eater. It starts its life in salt water and migrates upstream to mature. When it's ready to breed, it moves back to the ocean.
Its native range is between Vladivostock (Russian Far East) and South China, including Japan and Taiwan.
It has spread to Europe and North America.
Why this is a problem for New Zealand
This crab:
- can form dense colonies
- disrupts ecosystems
- eats aquatic plants, algae, detritus, fish eggs, and a variety of invertebrates
- displaces many species, like other crabs
- damages fishing nets and catches
- burrows, weakening and collapsing river and estuary banks
- can carry a liver fluke that harms humans.
Once established, aquatic pests are extremely difficult to eradicate.
How it could get here
This pest could arrive in New Zealand with ships, either as larvae in ballast water or within a ships’ sea chest. We have strict measures in place to reduce the chances of pests, like the Chinese mitten crab, coming here in ships.
Other countries suspect the live trade of crabs may have resulted in the crab establishing overseas. New Zealand has strict measures in place to keep this crab out.
Where it might be found
The crabs spend their first winter in brackish water. They migrate upstream into non-tidal parts of rivers and streams.
Adults usually live in burrows in muddy riverbanks. They can also be found around aquatic plants and marshes.
How to identify the Chinese mitten crab
Mitten crabs are easily recognised by the dense patches of bristles or hairs (setae) on their claws. The hairy patches are how they got their name. Males and females both have hairy claws, but the males are hairier.
Some features of the crabs include:
- a hairy 'mitten' with white tips on front claws
- distinctive notches between the eyes
- 4 spines on each side of the carapace (upper shell)
- carapace width generally 5cm to 7cm (up to 10cm)
- light brown to olive green carapace.
What to do if you see one
If you think you've found a mitten crab:
- photograph it
- take note of the location and any landmarks
- capture it (if you can)
- call 0800 80 99 66
Note: This information is a summary of this pest's global distribution and potential impacts to New Zealand.
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