Spiders and harvestmen

Devon is a hotspot for spiders and harvestmen with 450 species recorded.

They’re an important food for other wildlife and as carnivores, they’re natural pest controllers.

The horrid ground weaver spider lives in Plymouth quarries, the only place in the world it’s known to be.

What we need to do and where

Euophrys petrensis (a Teign Valley rock spider), A. Cunningham

Horrid ground weaver (Plymouth spider group), John Walters

Pale yellow orange spider

Scotolemon doriae (Plymouth spider group), John Walters

1. About

Spiders and harvestmen are arachnids, an ancient group of creatures that date back more than 420 million years. Unlike insects, arachnids have four pairs of legs instead of three, simple rather than compound eyes, and no antennae or wings. Spiders differ from harvestmen by having two distinct body segments rather than one. Many species of spider produce silk, which they weave into webs to catch prey or use to build nests, protect their eggs and to get around.

Arachnids are an important food source for birds, mammals, amphibians and reptiles. As they eat insects they help control species which damage crops or spread disease.

Devon’s arachnids can be found almost everywhere, from the coast to high moorland, in gardens and in our homes. Numbers vary widely according to habitat, but it has been estimated that there can be up to 800 spiders per square metre in uncut grassland. They all need:

Food: Spiders are carnivores and mainly eat insects. Most harvestmen also eat insects but will eat plants and dead animals too.

Shelter: Spiders and harvestmen hide from predators and build their webs or nests under rocks, in trees, burrows or inside buildings. Although spiders do not technically hibernate, many species will go into a state of dormancy over winter. Many harvestmen die off over winter, with only their eggs surviving.

Currently around 680 species of spider and 30 harvestmen are found in the UK. Around 450 of these have been recorded in Devon and 29 are listed as Devon Species of Conservation Concern. Those identified as Devon Special Species are discussed below.

Key pressures and opportunities

Species in this group vary hugely and so pressures and opportunities are discussed for each Devon Special Species and in the relevant habitat pages. 

2. What we need to do and where

Priority

Increase the abundance and distribution of spiders and harvestmen across Devon, particularly those identified as Devon Special Species.

See Find out more for links to more detailed information on this group including management advice and records.

Devon Special Species

Dartmoor bog spiders

Read more

This group of rare spiders is found in Dartmoor’s acidic wetlands, including the large peat bogs and smaller valley mires found along streams and old tin workings. All the habitats that support these spiders are within the North and South Dartmoor SSSIs. Good examples include Foxtor Mires (near Whiteworks disused tin mine) and Raybarrow Pool (near Little Hound Tor).

Little is understood about their exact habitat needs, but they are likely to be sensitive to anything that reduces the health of the bogs and mires, including climate change, atmospheric pollution, fire and other impacts to water levels and quality.

There are eight species in this group which are listed as Devon Species of Conservation Concern. Two of these are identified as Devon Special Species in their own right. See Find out more for a link to the more detailed profile written for this group.

a Money spider

Centromerus levitarsis

In Britain this spider is only found on Dartmoor (Foxtor Mires and Muddilake) and lowland raised bogs in Cumbria. Therefore, this sole southern population is vulnerable to local extinction. Further study is needed to better understand the requirements and behaviour of this spider.

a Money spider

Maro lepidus

This rare money spider occurs in Wales, northern England and Scotland but in southern England is only known on Dartmoor (New Bridge and Taw Marsh) and Bodmin Moor.

Actions

Protect and restore Dartmoor bogs and valley mires for rare spiders. 

  • Be aware of rare spiders when managing this habitat. Otherwise, actions are to maintain and restore healthy bogs and mires through actions such as light grazing and rewetting (blocking drainage channels). Manage surrounding land to maintain clean water and hydrological processes. See heath, bog, mire and species-rich rush pasture to learn more.

Where to focus actions

High Opportunity Areas: Dartmoor flushes and mires (existing) and Dartmoor deep peat. See Mapping.

Yellow-striped bear spider

Arctosa fulvolineata
Read more

A relatively large wolf spider only found in western Britain at Yelland in North Devon. This isolated population on the Taw (within the SSSI) inhabits less than 750m2 across two areas, one near the old Yelland Power Station and the other at the western end of Isley Marsh.

The spider is associated with unvegetated areas of estuarine foreshore, where it lives under stones embedded in the mud. The spiders form silk ‘retreats’ in gaps underneath the stones and can withstand being underwater during the highest tides.

Threats to the species include sea level rise due to climate change, isolation (the nearest population is in Hampshire), loss of open habitat and damage to habitat from infrastructure projects.

Actions

Maintain open habitat on the Taw estuary mudflats at Yelland for the yellow-striped bear spider.

  • Maintain open habitat through scrub clearance and protect habitat the spider uses and could potentially use. Coastal realignment schemes in or near the species zone should obtain expert advice and create new habitat with embedded stones on the estuary foreshore.
  • Survey the upper saltmarsh on the Taw Estuary, east to Penhill Point (SS517.343) and on the northern shore at Horsey Island (SS480.334).

Where to focus actions

High Opportunity Area: Taw estuary mudflats at Yelland – Cornwall to Morte Point Coastal Wildbelt. See Mapping. 

Plymouth arachnids

Read more

The three species in this special group depend on rocky sites in and around Plymouth. Two are considered to be Devon Special Species in their own right – the horrid ground-weaver spider may be one of the rarest spiders in the world and the hedgehog harvestman isn’t found anywhere else in the UK.

The third species in this group is Scotolemon doriae, a small, mite-like harvestman. It can be found under rocks embedded in the soil. In 2016 it was discovered new to the UK at Radford Quarry in Plymouth and has since been found at Ford Park Cemetery in Plymouth, in Bristol and Falmouth.

For more information on this group see the LNRS profile in Find out more.

Horrid ground-weaver

Nothophantes horridus

This small money spider was first discovered in 1989 at Cattedown quarry and is not known to occur anywhere else in the world. It’s named for its rather hairy body and legs: the Latin origin for the word horrid is bristly. It’s found under rocks in Cattedown, Billacombe and Radford limestone quarries and it may be at other sites in the area. The main threat to the species is from the development of old quarries. This may be an overlooked winter active Atlantic limestone spider which could possibly occur in areas on the west coast of Europe.

Spiky small bodied spider with long thin legs

Hedgehog harvestman

Nemastomella bacilliferum

A small harvestman with distinctive ‘spikes’ on its back. In the UK it is only found in Plymouth (at Billacombe, Radford Wood, Ford Park Cemetery and in the Forder Valley). It can be found sheltering in grass tussocks and on the underside of rocks. The main site at Billacombe is owned by Plymouth City Council and managed for the horrid ground weaver spider, and this management will also benefit this species. The hedgehog harvestman is a great flagship species highlighting the importance of nature reserves around Plymouth.

Actions

Manage Plymouth green spaces and quarries for rare spiders by allowing tussocky grasses to develop and protecting and creating open rocky areas.  

  • Continue to research into the ecology of the horrid ground-weaver and to survey sites across Plymouth (with a focus on limestone areas for the horrid ground-weaver) to better understand the distribution of these species.

Where to focus actions

High Opportunity Areas: Cattedown Quarry, Billacombe, Radford limestone quarry, Radford Wood, Ford Park Cemetery (a map of the spider areas is being produced with PCC and will be added to the viewer). See Mapping.

Moon spider and other Prawle cliff spiders

Read more

Read about this group on the Start Point to Bolt Tail coast invertebrate group page.

Teign valley rock spiders

Read more

The upper Teign valley between Castle Drogo and Steps Bridge provides perfect conditions for rare spiders. It’s thought to support a remarkable 127 species, one of which is found nowhere else in Britain and 17 of which are nationally scarce. The best areas are nine south-west to south-facing sunny slopes with broken shale which they can hide under. Thin soils on these slopes are partly stabilised by lichens and moss. 

Eight of the 127 species in this group are listed as Devon Species of Conservation Concern. These include the nationally rare jumping spider (Euophrys petrensis) which is found in other parts of southern England but hasn’t been seen anywhere else in Devon for over 20 years and a marshweb spider (Iberina candida) which isn’t found anywhere else in Devon.

The requirements of this group overlap with those of toadflax-leaved St John’s-wort (see Sunny rocky outcrop plants) and at least two nationally rare beetles, kugelann’s green clock beetle (Poecilus kugelanni) and the click-beetle (Cardiophorus vestigialis).

The gorge ground spider (Civizelotes civicus) has been identified as a Devon Special Species in its own right.

For more information on this group see the LNRS profile in Find out more.

A ground spider

Civizelotes civicus

This tiny spider (3.4-5.5mm) was discovered in the Teign Valley in 2020, the only known location in Britain. It’s found on three slopes near Castle Drogo (managed by the National Trust) and two at Dunsford (part of the Teign Valley Woods SSSI managed by Devon Wildlife Trust) and occupies less than 400 m2 of the potential 1 km2 of suitable habitat. 

Unlike spiders that construct webs, ground spiders are active hunters and instead weave silk nests under small pieces of broken shale where they lay their eggs. However, we don’t know much about this species and there is a lot still to learn.

Actions

Maintain and expand sunny rocky outcrops for rare spiders through light grazing and scrub control / coppicing.

  • Where possible survey rocky slopes at Prestonbury Castle, Deadmoor Common and Bigport Farm for potential populations of the gorge ground spider.

Where to focus actions

High Opportunity Areas: Upper Teign valley rocky outcrops (unmapped). Mapped as a Species Opportunity Area. See Mapping 

Actions for all spiders and harvestmen

Habitat management and creation

Spiders and harvestmen are found in the majority of habitats across Devon and will benefit from the actions set out on the Habitat pages.

Anyone who is managing or creating habitat for rare spiders and harvestmen should be aware of their needs. For more detailed information see the list of Devon Species of Conservation Concern and Find out more below.

Research and monitoring

Increase research and monitoring for spiders and harvestman.

3. Inspiration

This section will be finalised following public consultation. Please share any case studies and places to visit.

Case studies

Buglife project

Buglife is currently working closely with Plymouth City Council on a project to manage habitat and survey for the horrid ground-weaver spider and hedgehog harvestman. This work is funded through Natural England’s Species Recovery Project.

South West Peatland Partnership

The South West Peatland Partnership aims to restore 2,600 hectares of degraded peatland on Dartmoor, Exmoor, Bodmin Moor and West Penwith. While not focused specifically on spiders, it’s a good example of how landscape-scale projects can have multiple benefits, including the restoration of rare and special species.

Dartmoor peat bogs, with machinery in the distance and a low sun

Where to visit

Always follow the Countryside Code and keep to footpaths and sites that are managed for public access. 

Good places to see spiders and harvestmen are:

For information on visiting these and other sites that are open to the public please see the Explore Devon website.

4. Find out more

This section will be finalised following public consultation. Please share any links.

The Spider and Harvestman Recording Scheme website has information on all species.

The British Arachnological Society website has information about arachnids, including articles and opportunities to get involved.

Buglife’s Bug Directory has lots of information about invertebrates, including spiders and harvestmen. Information on their work on the horrid ground weaver spider and hedgehog harvestman can be found at Horrid Ground-weaver Project – Buglife projects

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