Deadwood invertebrates

Over 2,000 UK invertebrate species depend on deadwood.

It is one of the most important and yet generally under appreciated micro-habitats in Devon.

All dead and decaying wood is important for wildlife – from a pile of logs and twigs in the garden to entire decaying trees.

What we need to do and where
The moth faces the right, showing a side view that emphasises a large black and yellow headpiece that protrudes from its nose, curving upward and ending in a two pronged fork. The top front of the moth is bright yellow, with a black end half that has iridescent blue markings and a bright yellow dot. The underside of the moth is black and iridescent blue and the legs are black and white stripes. The moths eye is red.

Beautiful bark moth, Patrick Clement

A black beetle stands on a large green leaf with the photo being taken from above. The beetle has a long body, antennae and legs. There are six dulled yellow spots on its back.

Six-spotted longhorn beetle, Adam Colegate

The fly sits on a large green leaf. The fly has orange to black extra long legs, a large black and yellow circular body where the wings attach and a long recurved tail that is marked in yellow and black stripes.

Orange-sided comb-horn, Thierry Poulet

1. About

Decaying wood, whether associated with living trees, dead trees or branches lying on the ground, supports a multitude of specialist invertebrates. It’s one of the richest micro-habitats for flies and beetles. Exceptional communities are typically associated with Veteran trees because these contain a greater number and range of the necessary deadwood micro-habitats. Many of these trees are found in ancient Parkland and wood pasture, and feature rot holes created by the Goat Moth Caterpillar.  

Deadwood beetles characteristically favour the dry rot typical of old trees. In contrast, deadwood flies are associated with moist rot, typical of sap wood, younger trees and small bits of wood, even twigs, and many larvae are reliant on decomposing fungi, notably bracket fungi. Few species are restricted to just one type of tree but oak, beech, ash, aspen, elm and Horse Chestnut are noted as particularly good. Flowering shrubs that provide pollen and nectar, such as hawthorn and hogweed, are often necessary for invertebrates to feed on prior to being able to successfully breed.  

The Devon Species of Conservation Concern list includes additional species but it should be noted that a wide variety of species use deadwood at various life stages, such as the Blue Ground Beetle (a Devon Special Species) and Silver Streaked Beauty and Beautiful Bark moths (both in the Dartmoor woodland moth group). The deadwood fly group and Six-spotted Longhorn Beetle are discussed below.  

Key pressures and opportunities

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Habitat loss and degradation

Trees with ‘imperfections’ are felled, branches cleared away, and small wood from site management (such as forestry thinning or coppicing) meticulously removed, often to be burnt or chipped. Between 2010 and 2015 deadwood levels were unfavourable in 80% of native woodland habitat and 73% of non-native woodland habitat – the single biggest non-historical reason for woods being in unfavourable condition (National Forest Inventory 2020). Changes in habitat management through, for example, the reduction of coppicing or grazing, can lead to major structural changes in the woodland which alters the availability of deadwood and the situations it’s found in (such as under full shade rather than dappled light). This may also lead to an inadequate supply of nectar sources due to a lack of light availability. 

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Climate change

Other threats include climate change-related pressures such as the increasing frequency and severity of summer droughts and flooding, which pose a serious threat to veteran trees. 

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Disease

Climate change can lead to the increase of tree diseases such as sudden-oak-death, Dutch elm disease and ash dieback. These will have a major impact on long-term deadwood availability and its natural fluctuations. For this assemblage to flourish in the long-term it needs a continuous supply of deadwood, which depends on a mixed age-structure of trees in the landscape, rather than them all dying at once. 

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Invasive non-native species

 Invasive non-native species, such as Rhododendron, can alter numerous environmental variabilities, like how much sunlight reaches the forest floor, as well as outcompeting native flora for space. This can reduce deadwood availability in the long term (by threatening woodland regeneration) as well as reduce flowering species availability, needed for deadwood invertebrates at different life stages. 

2. What we need to do and where

Priority

Increase the abundance and distribution of deadwood across Devon.   

Devon Special Species

The fly sits on a large green leaf. The fly has orange to black extra long legs, a large black and yellow circular body where the wings attach and a long recurved tail that is marked in yellow and black stripes.

Deadwood flies

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Decaying wood is perhaps the richest of all micro-habitats for true flies and supports many specialist species.   

Although exceptional communities are associated with ancient trees, deadwood flies can also be found on twigs or in small rot holes. Beech, aspen, elm and Horse Chestnut are particularly good for deadwood flies. As larvae, many of these flies are reliant on decomposing fungi, notably on the fruiting bodies of macro-fungi like bracket fungi, and are associated with moist, white rot. 

This group contains a rich diversity of true flies, all of which are Nationally Scarce, unless stated otherwise. Notable species included in the group are the Orange-sided Comb-horn (Ctenophora pectinicornis), a Near Threatened cranefly (Rhipidia ctenophora), the Dark-saddled Sapeater (Brachyopa bicolor), a hoverfly, and the Freeloader or Jackal Fly (Madiza britannica) (provisionally Vulnerable). A list of all the species in this group can be found in the full deadwood flies expert profile. See Find out more below.  

A black beetle stands on a large green leaf with the photo being taken from above. The beetle has a long body, antennae and legs. There are six dulled yellow spots on its back.

Six-spotted Longhorn Beetle

Anoplodera sexguttata
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This rare beetle is an excellent example of how important it is to have a diverse range of deadwood available within the landscape. For two to three years, the larvae will feed exclusively on the heartwood of native broadleaves (such as oak, beech and hornbeam) that are being decayed by Oak Curtain Crust Fungus (Hymenochaete rubiginosa). The larvae will then pupate in dry sapwood in early spring before flying as adults during warmer weather.  

They are strongly attracted to a range of white flowers growing in sunny glades and wood edges, particularly umbel, and likely require the nectar before being able to breed. The beetle is thought to breed in old, barkless oak branches and trunks in semi-shade at wood edges, glades or rides, but has also been found in the open and on living trees where some dead heartwood is exposed.  

Of the six known British locations, the only definite colony in the southwest is located at Watersmeet SSSI, Exmoor. Key threats include the loss of suitable trees to sycamore (a densely shading invasive). Invasive non-native species such as Rhododendron and Japanese Knotweed are also present at Watersmeet and threaten much of the wildlife onsite through over-shading decaying wood and outcompeting native flora. However, the National Trust, who own the site, leave as much deadwood in-situ as possible and have begun a pollarding programme alongside the creation of new glades and wood pasture, as well as reduce grazing on the woodland edges.  

Actions for all deadwood invertebrates

Leave standing and fallen deadwood, collapsed trees and branches (even small ones), other than where there’s a clear safety issue and no alternatives. Pile up deadwood and fallen branches rather than chipping or burning them.

Ensure diverse nectar and pollen sources (eg. hawthorn) are readily available on sites with significant dead wood invertebrates. 

Eradicate non-native invasive species where possible. 

Increase monitoring and awareness of the value of deadwood habitat:

Increase education opportunities for arboriculturalists on the value of bracket fungi.  

Continue to record veteran and protect trees through the Ancient Tree Inventory. 

Other relevant actions

Deadwood is found throughout Devon and is valuable at any scale. However, some habitats support particularly rich deadwood communities and would benefit from the actions listed in the following pages:

3. Inspiration

Case studies

Killerton- National Trust 

Killerton is recognised as nationally significant site for its old trees and insect life. The estate is home to 1,500 veteran and ancient trees, with 200 classified as ancient. These trees provide crucial habitats for a diverse range of wildlife. 

Dr. Keith Alexander, one of the UK’s leading entomologists, conducted the survey and identified over 140 species of wood-decay invertebrates, including 72 species of saproxylic beetles and 68 species of two-winged flies. 

He said, “This is a remarkable total and firmly places Killerton as the most important site in the Southwest for its saproxylic population.”. 

Whiddon Deer Park 

Whiddon Deer Park is a particularly important site for deadwood flies in Devon and is an excellent spot for looking for some of the most attractive flies found in the UK (all associated with deadwood!). 

These include the Buff-tailed Bumblefly (Criorhina floccosa), the Orange-belted Plumehorn (Volucella inflata), both hoverflies, and the spectacular Orange-sided Comb-horn (Ctenophora pectinicornis), a cranefly. 

If you’re doing something to help nature thrive, please share it on the Devon Nature Recovery Delivery Map to inspire others to take action.

Where to visit

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

Killerton- National trust – see above

Whiddon Deer Park- Dartmoor – see above

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

4. Find out more

Deadwood flies full expert profile.docx 

Devon beauty spot hailed as one of UK’s ‘most significant’ – Devon Live 

Our work on the estate at Killerton | National Trust (scroll down to ‘what’s been happening’ to read about Killerton’s national significance for veteran trees and insect life). 

National Trust’s west Exmoor management plan 

Our woodland work on West Exmoor │Devon | National Trust 

Back from the brink ‘In pursuit of rare saproxylic invertebrates’ PowerPoint Presentation and Surveying for Deadwood-loving Invertebrates – Back From The Brink 

Create your own dead wood habitats – Buglife 

Lowland wood pastures and parklands – Buglife 

Cross taxa management guide for ancient tree and deadwood habitats – Buglife 

Buglife and back from the brink’s management guide for dead and decaying wood. 

Photo credits

Listed in order of appearance:

  • Beautiful Bark Moth- Patrick Clement
  • Six-spotted Longhorn Beetle- Adam Colegate
  • Orange-sided Comb-horn- Thierry Poulet
  • Orange-sided Comb-horn- Thierry Poulet
  • Six-spotted LonghornBbeetle- Adam Colegate

Draft