True flies

Over 3,060 species of fly have been recorded in Devon.

Few people know that flies are vital pollinators.

Six species which live in Britain are only found in Devon.

What we need to do and where
The bog hoverfly sits on the yellow flower of gorse. It is facing to the right rubbing its two forelegs together and has reddish-brown legs and furry chest. Its abdomen is yellow and grey stripes, shaped to a point towards the bottom of the fly. The two wings are clear and lie to either side of the fly. The background is blurred green vegetation with two more yellow gorse flowers.

1. About

True flies are those that belong to the order Diptera and are characterised by having just two wings.  In contrast, butterflies, dragonflies,  damselflies, caddisflies, stoneflies, mayflies and scorpionflies all have four wings and belong to different insect orders.

Devon is home to a remarkable range of true fly species, reflecting the county’s size and wide range of habitats. Over 3,060 species have been recorded here, 42% of the British total – and tens more are found every year. As not many people are recording flies, it’s likely that many hundreds of species are yet to be found or identified in Devon.

Flies matter! They carry out essential roles and so are a vital part of our natural system. They’re a critical source of food for a wide range of species such as frogs, fish, spiders, bats, birds and even some plants. They’re pollinators and decomposers. And the larvae (maggots) of some species live in soil where they help improve soil heath by aerating it and breaking down plant material.

True flies are found in all habitats across Devon, from gardens to saltmarshes and the wetlands of Dartmoor. Different species have adapted to live in different habitats and they all have different microhabitat needs. However, there are a few critical things that most flies need to survive.

Flowers, sap and fruit

Adult flies generally need a source of sugar from nectar, fruit or sap.    

Decaying matter

Larvae generally feed on decaying matter such as dead wood, manure or animal carcasses. Many species lay their eggs on decaying matter so their larvae have an immediate source of food. 

Water

Lots of flies like a moist environment and depend on habitats such as wet woodlands, mires and watercourses.

Shelter

Like all species, flies need sheltered areas where they’re protected from predators and harsh weather. 

There’s no systematic national monitoring of flies. However, it’s thought that many species have significantly declined in abundance and distribution, in line with national trends for insects.  

The small but thriving Devon Fly Group carries out surveys and has contributed to the LNRS. They’ve listed xxx species as Devon Species of Conservation Concern. xxx of these are identified as Focus Species that need specific actions  or attention. In Devon we have a national responsibility for xx flies, which are therefore listed as Devon Special Species.   

Key pressures and opportunities

camera

Lack of knowledge and public awareness

Its very likely that there are fly species in Devon which haven’t yet been recorded.  There are lots of things that we don’t know about the habitat requirements of species that have been recorded. In addition, there are no monitoring programmes designed to show countywide trends.  

Many people see flies as pests and are not aware of their rich range of species or how they contribute to a healthy, natural environment.

camera

Lack of protection

No SSSIs or County Wildlife Sites have been designated primarily for their flies. No fly species are legally protected, in the UK or in Devon.

camera

Loss of microhabitats

Many threatened flies need patches of specific microhabitat such as rot holes, seepages, soft cliff or the narrow zone of brackish water where small streams meet the shore. It’s easy to unintentionally destroy or overlook these habitats in management plans. Healthy habitats with diverse niche-opportunities and functioning natural processes will support a greater range and abundance of fly species.

camera

Habitat loss and lack of connectivity

Land uses such as intensive farming, forestry, urban development and infrastructure schemes have led to the loss and fragmentation of habitats across Devon. Lack of management of existing habitats, or changes to their management, can also lead to habitat loss. Many species are now living in isolated sites where populations cannot survive.   

Habitats such as wet woodlands are powerhouses of insect biomass production, particulary flies.  As such they are an important foraging habitat for other wildlife, in particular bats and birds. Despite their wildlife value wet woodlands are often overlooked.  

camera

Climate change

Rising temperatures, extreme weather events and seasonal changes disrupt life cycles, make less food available and alter habitats.

2. What we need to do and where

Priority

Increase the abundance and distribution of flies across Devon, particularly those identified as Focus Species

Focus species

The xxx Focus Species are discussed below. X have been put into groups with other invertebrates with similar requirements.  X have been brought together into groups of flies with similar requirements.  Two are discussed individually.

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

Wet woodland flies

Read more

Devon’s wet woodlands are home to an exceptional range and abundance of fly species. One wet woodland in west Devon has recently been estimated to produce 38 million flies per hectare per year. They support many nationally rare or scarce flies, including three that are nationally threatened (Macrocera longibrachiata, Neoempheria winnertzi, and Rhaphium fascipes) and two that are Near Threatened (Coenosia pudorosa and the Egle parvaeformis) .   

Other species that are nationally scarce (but not listed as Devon Species of Conservation Concern) include: the liverwort snipefly (Spania nigra), the sooty blacklet hoverfly (Cheilosia carbonaria), the rust fly (Chyliza vittata) and the lesser housefly (Fannia speciosa). See Find out more below for more species in this group. 

Flies in wet woodlands can be affected by pollution and lack of grazing. Wet woodlands are often permanently fenced off from adjacent wet grasslands because it’s thought that this will benefit their wildlife. However, research in Devon shows that the fly population is likely to be more diverse and richer in scarce species when cattle have controlled access to the habitat.  

Coenosia pudorosa is a Devon Special Species and therefore chosen as the flagship Focus Species for this group of flies which largely have the same habitat requirements. 

A muscid fly

Coenosia pudorosa  

Devon is thought to be the national stronghold for this small member of the housefly family as few recent records exist from the rest of the UK. The fly is strongly associated with wet woodlands, especially in river valleys. Little is known about its biology, but the larvae are probably predators of other fly larvae. In 2018, it was rediscovered near Shute in East Devon, the place where it was first nationally recorded in 1937. The fly is now known from about a dozen sites in Devon and appears to be well distributed within wet woodlands on the Culm Measures and Dartmoor. 

Actions

Manage and create a dynamic mosaic of wet woodlands across Devon 

  • Lightly graze with cattle to maintain a range of microhabitats. 
  • Identify key sites for flies and other invertebrates and bring them into favourable management. 
  • Create dynamic networks of wet woodlands across Devon as part of a mosaic with other habitats.  
  • See Wet woodlands for more information.   

Survey, monitoring and awareness 

  • Raise awareness of the high value of wet woodlands as part of a mosaic of habitats. Map the distribution of wet woodlands across Devon. 
  • Periodically survey key wet woodlands to determine the health of the Diptera assemblage, if only to see if they’re present or important species are absent. 

Where to focus action

Across Devon.  No Focus Areas have been identified for wet woodland flies.   

A cone-horn cranefly sits on a rock with a blurred rocky background. The cranefly has a thick, long abdomen that curves up in a similar shape to a scorpion with golden yellow sides and a central black stripe. These markings continue on the round, circular body and end in small all-black head with pointy mouth parts, clearly segmented antennae, and non obvious black eyes. The clear wings protrude either side of the fly, as do the very long orange-brown legs that sharply bend in the middle to hold the fly in place.

Deadwood flies

Read more

Read more on the deadwood invertebrate group page.

A variable meadow fly sits on a shiny green leaf in the centre of the frame. The fly has yellow legs and a striped black and yellow body with wings lying seperated, flat against the flies back. It has large black eyes and short sturdy black antennae above bright yellow mouthparts.

Variable meadow fly

Chrysotoxum elegans
Read more

Read more on the south and north Devon coastal invertebrate group page.

A spanish snout cranefly sits on a broad jagged leaf with other leaves from the same plant in the background. The fly has very long skinny brown legs with a bend halfway down. The clear wings lie flat against a very slim brown abdomen that connects to a globular body leading to a tiny but circular head with a long thin snout at leas three times the length of the head.

The spanish snout cranefly and other east Devon undercliff flies

Read more

Read more on the Sidmouth to Dorset coastal wildbelt invertebrate group page.

A devon red-legged robberfly sits on a grey rock against a blurred grey background. The fly has six reddy-orange legs, a mottled grey-brown round body with clear wings attached to it and lying flat against the slim brown abdomen which is roughly twice the length of the rest of the fly and has clear segments. Along the body are long, dark hairs. The small head is taken up by large grey eyes with short short antennae, below are the pale mouthparts.

Devon red-legged robberfly

Neomochtherus pallipes
Read more

Read more on the Start Point to Bolt Tail coastal wildbelt invertebrate webpage.

Lagoon snout cranefly and other Dawlish Warren mudflat flies

Read more

The saltmarsh and tidal mud flats in the ‘Bight of Dawlish’ at the mouth of the Exe Estuary support at least three threatened or near threatened flies that are found in few other areas nationally.   

The Bight of Dawlish is affected by rising sea levels as a result of climate change. The saltmarsh is showing signs of stress as it is squeezed between the sea and the artificial sea wall that protects the spit and its golf course.  

The tidal flats have also been put under pressure by coastal defence work on the sand dune system. For example, in 2018, the Environment Agency carried out major works to restructure the dune spit at its narrowest part.  

Lagoon snout cranefly

Geranomyia bezzii

This cranefly depends on tidal mudflats where its larvae feed on green algae. The weak-flying adults shelter in low-growing bushes such as sea purslane, just above the highwater mark. It’s only known to be in five other UK sites (on the south and east coasts), however these records are old.  

a housefly

Neolimnophora maritima

In the UK, this fly is only known to be at Dawlish Warren, although it hasn’t been seen since 2011 (in 1939 it was seen at Blakeney Point in Norfolk). Its precise habitat needs are unclear, but it appears to prefer the margin between foredune and tidal flat. 

a fly

Muscidideicus praetextatus

This is another species mainly associated with the north Norfolk coast and Dawlish Warren, although it is also known from a few other sites around the British coast. It’s restricted to saltmarshes, although adults may be found on nearby dunes or estuarine mud. Again, its precise habitat needs are unknown but given its very restricted distribution are likely to be highly specialised. The fly is vulnerable to extinction. 

Actions

Manage Dawlish Warren for the lagoon snout cranefly and other rare flies  

  • Consider the needs of this rare group of flies when managing and carrying out activities (including coastal defence works) at Dawlish Warren mudflats and saltmarsh.   
  • Support monitoring by the Devon Fly Group 

Where to focus action

Dawlish Warren National Nature Reserve. See mapping.

The north Devon sand dune flies

Read more

Read more on the sand dune invertebrate group page.

A satellite fly is partially emerged from a burrow in a dirt bank that takes up the background. The fly is an all over pale grey colour with dark hairs along its body and black legs. The abdomen and wings of the fly are not visible. The head is the same colour as the body with large red-brown eyes.

A satellite fly

Leucophora sponsa
Read more

A nationally rare fly that is dependent on the smooth-gastered furrow bee (Lasioglossum parvulum). It belongs to a group of flies known as satellite flies because they shadow their host bees to their nesting sites. The fly lays its eggs in the bee’s nest and the larvae feed on the pollen and nectar the bee collects.    

This fly has only been recorded seven times in the UK since 1960, all in southern England and southern Wales. In Devon it has only been found at Halsdon Nature Reserve, where a vast colony of furrow bees nests in the soft, eroding banks of the River Torridge.    

The fly’s main threats relate to the furrow bee and include loss of the riverbank due to high flows and flooding, and, if cattle are prevented from accessing the river’s edge,  too much stabilization and excess shading from trees.   

Actions

Maintain open banks along the River Torridge at and near Halsdon Nature Reserve.   

Remove encroaching trees where the fly is known to occur and allow cattle to access the river.   

Where to focus action

Halsdon Nature Reserve on the River Torridge.  See Mapping.   

In the centre of the frame is a tormentil globetail hoverfly resting on the top of a simple yellow flower that is only partially in frame. In the background there are many blurred blades of green grass. The hoverfly has a long, slim, cylindrical abdomen with black and yellow stripes. The thorax (the part of the body between the abdomen and head) is black and has two clear wings that are held either side of the body. The eyes are large and black and the mouthparts bright yellow. The legs are predominantly yellow, but black closer to the body.

Tormentil globetail hoverfly

Sphaerophoria potentillae
Read more

The tormentil globetail hoverfly is a dainty black and yellow-banded hoverfly that is known from just three sites in the UK. Two of these sites, Beaford Moor SSSI and Common Moor (East Putford) SSSI, are in north Devon and the third is in Cornwall. Although the hoverfly is found elsewhere in north-western Europe, it’s considered rare throughout its range and is vulnerable to extinction, making every population significant.  

The species is very hard to identify unless it is examined under a microscope.  

The tormentil globetail hoverfly lives in wet, acid culm grasslands where it seems to prefer areas with tussocky purple moor grass and wet runnels. Adults feed on tormentil flowers and larvae are likely to feed on aphids. Threats may include heavy cattle grazing, scrub invasion and winter burning, although more research into its precise habitat requirements is needed. Given the hoverfly’s preference for very wet conditions, climate change may also be a threat as it continues to cuase more frequent and more severe summer droughts. 

Actions

Manage and restore a network of wet, species-rich culm grassland sites. 

  • Manage existing and potential sites to provide the hoverfly with suitable  microhabitat, in particular maintaining tall patches of purple moor grass clumps with runnels flowing through them. See Wetland mosaics for more information on Culm grasslands.   

Survey, research and awareness 

  • Survey and monitor the two existing sites and research requirements. 
  • Raise awareness of the tormentil globetail hoverfly and its needs, in particular among land managers. 

Where to focus action

Where to focus action 

A Focus Area has been mapped for the tormentil globetail hoverfly based on where action is most needed to restore and link populations. See Mapping.    

The bog hoverfly sits on the yellow flower of gorse. It is facing to the right rubbing its two forelegs together and has reddish-brown legs and furry chest. Its abdomen is yellow and grey stripes, shaped to a point towards the bottom of the fly. The two wings are clear and lie to either side of the fly. The background is blurred green vegetation with two more yellow gorse flowers.

Bog hoverfly and other valley mire flies

Read more

Wet, acid, species-rich mires are found across Devon. These include the valley mires on Dartmoor (many of which are within Rhos pasture mosaics), the spring line mires of the Blackdown Hills and smaller areas of valley mires which form part of a heathland mosaic in areas such as the East Devon Pebblebed Heaths. 

These damp, vegetated areas provide perfect habitat for flies.  Many of these sites are protected as SSSIs or are within nature reserves. However, their management tends to focus on species that are better known and easier to monitor.

Two species have been identified as Focus Species. 

The bog hoverfly sits on the yellow flower of gorse. It is facing to the right rubbing its two forelegs together and has reddish-brown legs and furry chest. Its abdomen is yellow and grey stripes, shaped to a point towards the bottom of the fly. The two wings are clear and lie to either side of the fly. The background is blurred green vegetation with two more yellow gorse flowers.

Bog hoverfly

Eristalis cryptarum

This charismatic hoverfly is critically endangered in the UK,  now known from just a few mires and flushes on Dartmoor. The adults, which fly low and fast, feed on nectar from marsh marigold, bog-bean and devil’s-bit scabious. The larvae are aquatic with long breathing tubes.

There has been no concentrated survey effort since 2012. However, the hoverfly has been seen most years, including at a few new sites such as DWT’s Emsworthy Mire reserve. In 2018, the University of Exeter tested whether the species could be detected using environmental or free DNA, but this was not successful.  

Further research into other habitat requirements is urgently needed. However, the hoverfly’s small populations and elusive nature make this challenging.  

In the absence of better information, the priority is to maintain current management at sites where the hoverfly exists and to create networks of similar sites to ensure its future survival. 

Hydrophorous albiceps

Hydrophorous albiceps

Hydrophorous albiceps is the other Focus Species in this group. To date it has only been found at Throwleigh Common on Dartmoor – do we know anything about its needs?   

Actions

Manage and restore a network of healthy valley mires, particularly for bog hoverfly

  • Restore and manage a network of valley mires that could be suitable for bog hoverfly. Create corridors and stepping stones of flower-rich habitat to aid dispersal. 
  • At sites with bog hoverflies, maintain current grazing levels and the same type of livestock. Larvae could be dependent on features as specific as the right type of dung or water-filled hoof prints.
  • Ensure there is abundant marsh marigold, bog bean and devil’s bit scabious.  

Survey, monitoring and awareness

  • Survey the condition and management of known sites on Dartmoor, including microhabitats, to better understand habitat requirements. 
  • Continue to use new technology such as environmental DNA to survey for presence, including larval habitats. 
  • Raise awareness of the critical status of the bog hoverfly among landowners and managers, as well as the importance of valley mires and water quality.

Where to focus actions

A Focus Area has been mapped for the bog hoverfly. Hydrophorus albiceps is also found in Dartmoor valley mires and will benefit from the same actons in this area.  See Mapping.

See the LNRS viewer for mapped vallye mires and Focus Areas:  Dartmoor valley mires, East Devon scarp slopes, North Devon Culm and East Devon Pebblebed Heaths.  

Actions for all true flies

Habitat management

Flies are found in all habitats across Devon and will benefit from the actions set out in the Habitat pages. 

3. Inspiration

4. Find out more

All fly records from the Devon Fly Group are sent to Devon Biodiversity Record Centre.

The Hoverfly Recording Scheme webpage has records for hoverflies.

Join the Amateur Entomologist Society to see their publications and take part in their events.

Ball, S.G. & Morris, R.K.A. 2014. A review of the scarce and threatened flies of Great Britain. Part 6: Syrphidae. Species Status 9: 1-130 Joint Nature Conservation Committee, Peterborough. 

Other flies of note in the groups discussed above

Valley Mires

Craneflies: Tipula holoptera pNS and Triogma trisulcata ?RDB3/I  

Fungus gnats: Rymosia coulsoni NS 

Dolichopodids:  Hydrophorus albiceps NT, Campsicemus compeditus, C. alpinus and Dolichopus phaeopus NS 

Hybotids: Syndyas nigripes NT (Blackdown springline mires)  

Hoverflies: Eristalis cryptarum CR,  Platycheirus perpallidus NS, P. nielseni NS and P. ramsarensis NS 

Scathophagids (dung flies): Pogonota barbata and Cordilura rufimana 

Wet woodlands

Fungus gnats: Allodia neglecta NS, Exechiopsis membranacea NS, Grzegorzekia collaris NS, Macrocera longibrachiata VU, Mycetophila strigatoides NS, Neoempheria winnertzi VU, Rymosia britteni NS and Trichonta pulchra NS 

Craneflies: Dicranomyia lucida NS, Gonomyia abscondita, Nephrotoma dorsalis, Lipsothrix nervosa, Molophilus corniger NS, Paradelphomyia nielseni NS and Thaumastoptera calceata NS 

The liverwort snipefly Spania nigra NS 

Dolichopodids: Achalcus bimaculatus NS and Gymnopternus angustifrons NS 

Lauxanids: Homoneura interstincta/mediospinosa NS, Homoneura notata NS and Sapromyza quadricincta NS 

The sooty blacklet Cheilosia carbonaria NS (a hoverfly) 

The rust fly Chyliza vittata pNS 

The anthomyiid Egle parvaeformis pNT 

The muscids Coenosia pudorosa NT, Helina abdominalis pNS, Helina vicina pNS and Phaonia magnicornis pNS 

The lesser housefly Fannia speciosa NS

The hornet robberfly (Asilus crabroniformis) is another species of note that is discussed in the dung invertebrates group.

Search this site:

clear
Beta