Insects - True Flies


Image above by Rob Wolton
Zipperback hoverfly Chrysotoxum elegans - Least concern but nationally scarce

This attractive hoverfly is a striking wasp mimic. Strongly associated with Devon, its national range and populations are thought to be declining. The larvae have not been found but are likely to be associated with ants. This species favours sunny south-facing coastal slopes, often in clearings among gorse and blackthorn scrub. No information is available on trends in range or abundance of this fly in Devon. However, the loss of coastal grassland to bracken, scrub and other rank vegetation, reflecting a lack of grazing, is likely to be causing some decline. The planting of new woodlands on scrubby coastal slopes, rather than managing the slopes to create a mosaic of grassland and scrub, may constitute a further threat.
Map to show the Devon distribution of this species



A fly Coenosia pudorosa - Near threatened and nationally scarce

Devon appears to be the national stronghold for this small member of the housefly family. Elsewhere in the country very few recent records exist. The fly is strongly associated with wet woodlands, especially in river valleys. Little is known about its biology, but its larvae are probably predators of other fly larvae. In 2018 this species was re-found near Shute in East Devon, the place where it was first recorded nationally, back in 1937. The fly is now known from about a dozen sites in Devon and would appear to be well distributed within wet woodlands on the Culm Measures and Dartmoor. Wet woodlands, however, are at risk of inappropriate management or even removal as a consequence of their current low profile within the county.

Map to show the Devon distribution of this species


Image above by Rob Wolton
A cranefly Dicranomyia goritiensis - Least concern, nationally scarce

This is a cranefly of south-western coasts, breeding on steep moss and algal-covered rock faces with water constantly flushing over the surface. It is only known from two inland sites in the UK, one of these being on Dartmoor, at Meldon Aplite Quarry. No information is available on trends in range or abundance of this fly in Devon. No patches of suitable habitat are known to have been lost in recent years, and the fly is frequently encountered where its specific habitat requirements are met, so the population is probably stable. Nonetheless, the species is at risk from coastal development, changes in water chemistry as from septic tank discharges, and from recreational pressures such as rock climbing.

Map to show the Devon distribution of this species


A parasitic fly Dionaea aurifrons - Data deficient, nationally rare

The only known sites in the British Isles for this bristly sand dune fly are both in Devon: Braunton Burrows and Woolacombe (Putsborough). The larvae are parasites of spurge bugs Dicranocephalus. The adults are on the wing from May to August, nectaring on flowers of ragwort and spurges. This fly has not been seen since 2016, when it was last found at Braunton Burrows. However, there has been no focussed effort to re-find it and there is no reason to suspect that is has been lost. The work being undertaken at Braunton Burrows through the Dynamic Dunescapes project, commencing in 2020, should benefit the spurges which are the foodplant of the bugs which are the fly's host, so may lead to a population increase. Woolacombe dunes, a very much smaller system, are now probably no longer suitable for the fly: it was last seen here in 1948.


Image above by Andrew Cunningham
Bog hoverfly Eristalis cryptarum - Critically endangered and nationally rare

This charismatic hoverfly is now extremely rare and known in the UK only from a few mires and bogs on Dartmoor, having been lost from sites elsewhere. Adults nectar on the flowers of marsh marigold, bog-bean and devil's-bit scabious. Its larvae have not yet been found but will be aquatic and have long breathing tubes ("rat-tailed"). There has been no concentrated survey effort since 2008. However, individuals have been subsequently seen at several sites. In 2018, an individual was seen at Emsworthy Mire Devon Wildlife Trust reserve, a new site for the species, and in 2019 it was seen at two known sites. In 2018, Katherine Mitson (Exeter University) tested whether the species could be detected using environmental or free DNA but was not successful. The status of the hoverfly remains precarious - further research into its precise habitat requirements is required as is further monitoring. However, the small populations and elusive nature of the fly makes this challenging. The hoverfly is likely to be at risk from changes at its breeding sites in hydrology, water chemistry and livestock grazing, and from scrub invasion.

Map to show the Devon distribution of this species


Image above by Rob Wolton
Lagoonal sea-snout cranefly Geranomyia bezzii - Vulnerable and nationally rare

This small cranefly is known in the UK from only six sites along the south and East Anglian coasts. It has not been seen at most of these for many years. Dawlish Warren is an important extant site. The larvae are unusual in feeding on tidal mud flats on green algae. The adults, which are poor fliers, shelter in low-growing bushes such as those of sea purslane just above highwater mark. Coastal defence works at Dawlish Warren carried out by the Environment Agency in 2018, which involved restructuring the neck of the sand dune spit adjacent to the mudflats used by the cranefly for breeding, put the species at risk, when surplus sand was spread over the flats. The work was carried out initially in ignorance of the presence of the fly (reflecting inadequate environment impact assessment): the sand spreading was carried out after the EA and Natural England had been alerted to the presence of the fly. Fortunately, the fly was re-found in summer 2019. The population remains vulnerable to changes in water quality and probably to rising sea level.

Map to show the Devon distribution of this species


Image above by Rob Wolton
A cranefly Helius hispanicus - Endangered and nationally rare

This long snouted cranefly is known in the British Isles only from two or three seepages running down the soft coastal cliffs of the Axmouth to Lyme Regis Undercliffs, at Haven Cliffs close to Axmouth Harbour. Two other Devon Special Species, Morris's Wainscot and the Broad-faced Burrow Bee, occur in the immediate vicinity, along with several other very rare invertebrates. The last records of the cranefly were of a male and female in June 2016. The seepages it occupies were visited in August 2019 and appeared unchanged. No particular threats were noted. However, vigilance is required to ensure that no works such as cliff stabilization or recreational provision affect the fly's very particular habitat requirements.



Least cigar-gall fly Lipara similis - Endangered and nationally rare

This fly is dependent on reed beds, the larvae developing in galls on the stems of common reed. Otherwise known only from a few sites in East Anglia and one in the New Forest, it was discovered in 2015 at two sites in Devon, the Axmouth-Lyme Regis Undercliffs National Nature Reserve and the upper reaches of the Exe Estuary. At the Exe Estuary it occurs both in the tidal reedbeds at the head of the estuary and in the Old Sludge Beds, both Devon Wildlife Trust nature reserves. Another, even rarer, fly of the same family, Cryptonevra consimilis, is dependent on the galls caused by L. similis: it was found at the Exe Estuary reedbeds in 2016. There have been no subsequent attempts to re-find either species. Since the habitats remain more or less unchanged (other than sea water incursion into the Old Sludge Beds leading to willow carr loss), and the Least Cigar-gall Fly can survive in both freshwater and saline situations, there is no reason to believe that it does not survive at either the Exe Estuary or the Undercliffs. However, the extent and quality of available reedbed does need to continue to be monitored within the nature reserves concerned: both L. similis and C. consimilis are at risk from the loss of reedbed, whether through scrub invasion, rising sea levels or some other factor.

Map to show the Devon distribution of this species


Image above by Rob Wolton
A totem hoverfly Sphaerophoria potentillae - Vulnerable and nationally rare

This small yet attractive hoverfly is rare throughout Europe and known only from only three locations in the UK, two of which are SSSI Culm Grassland sites in northern Devon (Beaford Moor and Common Moor (East Putford)). Here it is associated with tussocky purple moor grass beside small runnels. It has not been found on well-grazed or frequently burnt places. The larval biology is unknown. This fly was last seen in 2014 at Common Moor and 2015 at Beaford Moor. A brief attempt to find the fly at Common Moor in 2019 was unsuccessful. Both sites are under Countryside Stewardship agreements. An extensive programme of Culm grassland restoration at Common Moor is underway, led by the Devon Wildlife Trust which is now aware of the fly's presence. Rob Wolton intends to carry out a more thorough search of the site for the fly in June 2020, both to confirm its continued presence and to inform site management. A monitoring visit to Beaford Moor to check that the habitat conditions remain suitable (as far as they are known) is required. The fly is threatened by pond creation, heavy cattle grazing, scrub invasion and probably winter burning. Further research into its precise habitat requirements is needed.

Further sources of information:

The Dipterists Forum

Cranefly Recording Scheme

Hoverfly Recording Scheme