First evidence of Chinese mitten crab breeding in Ireland

Biodiversity Ireland have issued an Invasive Species Alert for Chinese mitten crab (Eriocheir sinensis)

One berried female with eggs showing signs of development to Zoea stage, was captured by net on 25th January 2021 in Waterford harbour. Another female was photographed 25th December 2020. Chinese mitten crab has been record twice previously in Waterford harbour, one individual in 2006 and 16 crabs in 2009. 

See Invasive Species Alert from Biodiversity Ireland for further details.

Potential Impacts:

    • When population densities are high, the species causes considerable damage to soft sediment banks through burrowing which increases erosion and might affect flood defences. This has been documented in Europe and North America.
    • In Ireland there is concern that the species may impact on the native and endangered White Clawed Crayfish as well as fish species such as the protected Twaite Shad fish.
    • Likely to have widespread impacts on native fish and invertebrate species as there are no native freshwater crabs in Ireland.
    • Additional negative impacts, such as loss of biodiversity and recruitment of commercial species are expected.
    • The species may impact on the endangered and protected white clawed crayfish (Austropotamobius pallipes) as it has been shown to act as a host for Crayfish plague (Aphanomyces astaci) under lab conditions.
    • There are economic impacts associated with introduction of this species. To date, in Germany, the species is known to have cost at least 80 million Euro in monetary value.
    • The Mitten Crab is also an intermediate host for the mammalian lung fluke Paragonimus ringer, known to infect humans.

Life cycle:

The Chinese mitten crab life cycle includes phases spent in the marine, brackish and freshwater environments. Most of its life cycle is spent in rivers as an adult but it must migrate to deep, open saltwater locations to reproduce. In the spring, the eggs hatch into larvae and after about six to seven weeks these metamorphose into juvenile crabs, which then migrate back up the river into freshwater to complete the life cycle.

Field signs:

As Chinese mitten crab burrow into river banks, they leave behind holes about 3 cm in diameter. Dead bodies (carapaces) may also be found washed up but positive identification would require the mittens to be present. There are no other freshwater (river) crabs present in Ireland. 


In Ireland please submit your suspected sightings (if possible with a photograph) through this online form or the Biodiversity Data capture app.

In Northern Ireland please submit your suspected sightings (if possible with a photograph) to CEDaR online recording or via the iRecord app

Invasive Species Ireland

Invasive Species Ireland