Crustaceans and myriapods

Habitat 

The white-clawed crayfish is globally endangered and legally protected. It is the largest UK native invertebrateAn animal that doesn't have a backbone, such as insects, spiders, worms, crabs and slugs. More and our only native freshwater crayfish. They need clean, well-oxygenated streams and rivers with a neutral to slightly alkaline pH with readily available calcium to form the exoskeleton. White-clawed crayfish are very sensitive to pollutants, especially insecticides and agricultural inputs such as ammonia and to high silt levels. They are occasionally found in lakes and ponds.

They need plenty of hiding places under rocks, vegetation and tree roots and eat plants, algae, invertebrates and small fish. In turn they are prey for a range of species including otters, various waterbirds and fish such as Atlantic salmon. Their lifecycle includes an egg stage, a juvenile stage and an adult stage and they can live for more than seven years.

 In Devon all the rivers are sub-optimal for white-clawed crayfish in terms of both habitat and water quality, which may be why the animals are on average smaller in size than most other populations and live at very low densities.  

Population

White-clawed crayfish were abundant in England and Wales up to the 1950s when the population declined due to pollution (especially chemicals such as organophosphates used in sheep dips) and habitat degradation.  In the 1970s American signal crayfish were introduced as a farmed species. Unfortunately these crayfish escaped and rapidly spread across the country. Signal crayfish dominate native crayfish and will outcompete them for food and habitat. They also carry a fungal disease called crayfish plague which is fatal to native crayfish.  

As a result of all these pressures there was a huge decline in the white-clawed crayfish population during the 1980s and 90s with up to 95% of populations lost in southern England. The majority are now found in northern England but populations continue to decline.

They have never been widespread in Devon as our rivers are generally too acidic. Historically they were present in East Devon catchment rivers, the Clyst, Culm, Axe, Otter and Creedy Yeo. They are now only found on the Culm and Creedy Yeo but largely due to the presence of signal crayfish, pollution, low river levels in summer and damaging floods in winter, the populations continue to decline and they are likely to become extinct in the next 20 years. See Find out more for the detailed paper on white-clawed crayfish written for the LNRS by the EAEnvironment Agency More. This includes information on the hatchery at Wildwood Devon and the Saving Devon’s Native Crayfish Project.  

Habitat

Though their transparent body can make them hard to spot, fairy shrimps are unmistakeable once seen. They swim upside down and can grow up to 3 cm. They have a long, forked tail and 11 pairs of swimming legs.

Fairy shrimps live in small ponds and puddles which dry out in the summer. These are generally found on heaths, moors and grasslands where livestock trampling maintains open, sparsely vegetated areas or where quarry or miliary vehicles create deep, wet rutted areas along tracks. They are thought to prefer temporary ponds as they have fewer predators such as fish and dragonfly larvae.

Eggs lie dormant in dry mud and hatch when rain refills the pool. Fairy shrimp feed mainly on algae (which can turn them green) but also eat organic material and small invertebrates like water fleas.

Fairy shrimps are a flagship species for temporary pools, and important invertebrate habitat supporting many rare species.

Population

The fairy shrimp has always been a very scarce and threatened species in the UK and its population is vulnerable to extinction. It is a protected species which makes it illegal to knowingly disturb or harm it.

In Devon there are fairy shrimp scattered across the county. The commons of southwest Dartmoor have the greatest concentration of colonies and there are also recent sites on clifftop grassland in the Branscombe area and on the north Devon culm grasslands. Most sites have no formal protection.

Fairy shrimp habitat has been lost on some sites where a reduction in livestock has led to open water becoming overgrown or densely shaded by tall vegetation such as rushes and/or scrub.

Note that the National Biodiversity Network map doesn’t include most of the recent records of this species in Devon and that there have been no recent targeted surveys in Devon.

The British cave shrimp is only known from Devon and Cornwall. Along with its close Irish relative (N.irlandicus) it’s thought to be the oldest animal species in the British Isles and to have been here for at least 19.5 million years!

Little is known about this species, but it’s widely distributed in Devon’s underground groundwater aquifers and is found in caves, mines, springs, wells and boreholes. As they live in total darkness that are blind and have extra-long legs and antennae to detect food (microorganismsAn organism that can be seen only through a microscope. More and organic matter). The main pressures are thought to be pollution of groundwater from sewage and fertiliser run-off.  

This threatened millipede is found around Kingsbridge and Dartmouth in south Devon and isn’t known anywhere else in the world.  

It was first found in 1992 at Slapton Ley NNR on coastal vegetated shingle. A 1995 survey recorded it in at least ten other sites in a restricted area of south Devon stretching from Kingsbridge in the west to Brixham. The millipede has been found in leaf litter under broadleaved trees in woodlands (often where there is a layer of Ivy in the understorey) on sea cliffs and scrubby coastal grasslands. Consultation: find out where the sites are and list them or say where to find information.

The vegetated shingle at Slapton is under considerable threat from rising sea levels associated with climate change and areas have been lost through recent storm surge events.  At its southern end the shingle is constrained from moving inland by the ley, A379 road and coastal defences.  None of the other sites have any formal protection making them vulnerable to loss, particularly sites close to Brixham and Dartmouth where development pressure is high.

No surveys have been undertaken since 1995 and there are no current conservation projects focusing on this threatened species.