Spiders and harvestmen

There are thought to be 235 species of spider and harvestmen in Devon.

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. Cunningham

Horrid ground weaver, John Walters

Scotolemon doriae, 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, and 235 of these have been recorded in Devon. 29 are Devon Species of Conservation Concern and of these 11 have been identified as Focus Species.  Devon is a stronghold for xxx which are listed as Devon Special Species. needs agreeing

Key pressures and opportunities

Add others later

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Habitat management

Poorly managed habitat reduces the quantity and quality of niches available to rare and specialised species of spiders and the prey available to them.

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Climate change

Changing temperatures and rainfall patterns affect spiders and harvestmen as both predators and prey. The increasing frequency of floods, droughts and fires can further damage their habitats.

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Lack of awareness

…so risks from infrastructure projects, conservation management etc

2. What we need to do and where

Priority

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

Focus species

For this strategy, where the 11 Focus Species need similar actions they have been grouped together. Note that the majority of the 29 Species of Conservation Concern occur in these groups. 

See Find out more below for where to find detailed species records.

Dartmoor bog spiders

Read more

These rare spiders are 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 (nearLittle 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. Eight bog and mire species are listed as Devon Species of Conservation Concern. Two of these are identified as Focus Species and one as a Devon Special Species.

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 upland mosaic for more details.

Where to focus actions

  • Dartmoor peat bogs and valley mires Focus Areas. 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. An immediate threat to this species in Devon is a proposed planning application for the old Yelland Power Station site, which could damage vital foreshore habitat.   

Actions

Protect mudflats on the Taw estuary at Yelland for the yellow-striped bear spider.

  • 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.
  • Maintain open habitat through scrub clearance. 

Survey

  • 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

Taw estuary mudflats at Yelland. See Mapping. 

Plymouth arachnids

Read more

All the species in this assemblage depend on rocky sites in and around Plymouth. The group includes what may be one of the rarest spiders in the world, as well as a harvestman found nowhere else in the UK

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.

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 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.

a Harvestman

Scotolemon doriae

This small, mite-like harvestman 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.

Actions

Manage Plymouth green spaces and quarries for rare spiders.  

  • Carefully manage existing and potential spider habitats, allowing tussocky grasses to develop and protecting and creating rocky areas.

Survey and research

  • Continue to research into the ecology of the horrid ground-weaver.
  • Continue 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

Plymouth Green Spaces Focus Area. See Mapping.

South Devon cliff spiders

Read more

See Start Point to Bolt Tail coastal wildbelt assemblage to read more

Teign Gorge rock spiders

Read more

The upper Teign Gorge between Castle Drogo and Steps Bridge provides perfect conditions for rare spiders and is thought to support a remarkable 127 species, one of which is found nowhere else in Britain. 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 these species are listed as Devon Species of Conservation Concern. Of these, three are Focus Species and one is a *Devon Special Species.

Gorge 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.

a Jumping spider

Euophrys petrensis

This species is nationally rare and, although it can be found in other parts of southern Britain, it hasn’t been found elsewhere in Devon in the last 20 years. This is probably due to loss of heathland and the spiders’ poor ability to disperse but may also be due to lack of survey.

a Marshweb spider

Iberina candida

A nationally rare species which is found in the south of England, generally in coastal habitats. In Devon it is only found in the Teign Valley.

Actions

Maintain and expand sunny rocky outcrops for rare spiders 

  • Maintain open habitat through light grazing and scrub control and prevent shading by  coppicing surrounding trees. 

Survey

  • 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

Teign gorge rocks Focus Area – see Mapping 

Actions for all spiders and harvestmen

Habitat management

  • Spiders and harvestman will benefit from actions identified to manage, create and connect a mosaic of habitats across Devon. See Habitats pages. The following habitats are particualrly important for rare spiders:
  • Bogs and valley mires, gardens and urban greenspaces, coastal cliffs, heathland    check this list
  • Anyone who manages habitat with 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. 

Awareness

  • Raise the profile of spiders and their needs across Devon, in particular rare focus species such as the horrid ground-weaver which isn’t found anywhere else in the world.

Research and monitoring

  • Increase research and monitoring as spiders and harvestman are routinely under-studied, under-monitored, and therefore misunderstood. The more we know about a species, the more likely we are to protect it.

Habitat management

Some Devon habitats are critically important for spiders and harvestmen. These include: 

3. Inspiration

Case studies

Buglife

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.

Where to visit

Talk to James about what it is appropriate to say.  Would be good to talk about some common spiders and where to see them (gardens!) but not sure about sites? 

4. Find out more

More links – including how to get involved in Devon?

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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