SPECIES MANAGEMENT SHEET robberfl y ( crabroniformis)

The Hornet robberfl y is a predatory fl y Life cycle that can grow to more than an inch long, The adults can be seen from late July making it arguably the largest fl y in the to early October, but are most frequent UK. This is a distinctive with its in August. Both adults and larvae are hairy face, thick black proboscis, brown predatory. The adults will feed on a variety of , including , beetles, body and yellow tail, although the latter bees, wasps and other fl ies. The robberfl y can be hidden beneath the brown-tinged larvae prey on larvae, wings when the fl y is at rest. Hornet especially the larvae found in the soil robberfl ies are associated with beneath animal dung. Hornet robberfl ies grazing, particularly by cattle, as the lay their eggs on edges of dry cow pats, dung provides habitat for the larvae. horse dung, under rabbit droppings or on nearby vegetation. The adults Hornet robberfl ies are most active in may be seen sitting on other temperatures above 20°C, below 16°C types of dung, such as sheep they are unlikely to fl y and may be or dog, but they are more likely diffi cult to fi nd. The adults may hang or using these as hunting perches lie upside down when resting, exposing rather than for egg-laying. their brown underparts which act as Distribution map camoufl age. Adults can be territorial, The Hornet robberfl y has a with males establishing larger territories Dark green = recent records (after 1980) widespread distribution in southern Light green = historic records (before 1980) than the females, but they may also Britain but its range is declining and behave more gregariously. Females it has already disappeared from East disperse further and are more likely to Anglia. This robberfl y has also suffered discover new habitats where they can signifi cant declines in other Western lay their eggs. European countries. Threats and causes of decline this species need to be combined with cattle, horse or The removal of livestock or substantial changes in rabbit grazing where this is not already implicit. grazing can cause local extinctions. Hornet robberfl y populations disappeared from sites in Hampshire Environmental stewardship options when cattle were replaced by sheep. The use of HLS options avermectins against gut parasites causes dung to be HC12-14 Maintenance/restoration/creation of wood insecticidal and often sterile. This results in the loss pasture and parkland of prey items for the larvae. HK6-8 Maintenance/restoration/creation of species rich, semi-natural grassland Habitat HK15-17 Maintenance/restoration/creation of The Hornet robberfl y favours heaths and downs grassland for target features and is thought to prefer the light, well-drained soils HO1-2 Maintenance/restoration of lowland heathland associated with these habitats. It is not restricted to HO3 Restoration of forestry areas to lowland these habitats, however, and is occasionally found in heathland open woodland clearings or even in marshland. HO4 Creation of lowland heathland from arable or A supply of cattle or rabbit dung is a critical factor, at improved grassland least through the summer and early autumn, as well HO5 Creation of lowland heathland on worked as a supply of other invertebrates for the adults and mineral sites larvae to feed on. HR1 Cattle grazing supplement

Habitat management ELS options Ensure cattle, horse or rabbit grazing from at EE1-3 Buffer strips on cultivated land least early July to mid-September to coincide with EE4-6 Buffer strips on intensive grassland emergence and egg-laying times. Exclude livestock EK1 Take fi eld corners out of management from sites for a month after avermectin treatment and avoid bolus treatments. A continuity of grazing References activity across a wider area will benefi t this species This sheet can be accessed on the web at www.buglife.org.uk as females will disperse between suitable areas in Clements, D.K. & Skidmore, P. 2002. The autoecology of the hornet robberfl y (Asilus crabroniformis) L. in Wales. CCW Contract Science the search for new breeding sites. Rabbit grazing Report no. 525. is, in moderation, good for invertebrate populations Painter, D. 1997. Monitoring the Hornet robberfl y (Asilus as it creates a more diverse vegetation structure crabroniformis) at Crymlyn Bog NNR 1997. Countryside Council for Wales. than other grazing regimes. It also leaves scrapes Pinchen, B.J., Denton, J.S. & Bird, D.R. 1997. The hornet robberfl y and burrows. In areas where rabbits need to be (Asilus crabroniformis) Linnaeus. Adult behaviour at selected sites controlled it is better to limit the damage they cause in Dorset, Hampshire and Surrey in 1997. English Nature Research Reports No. 274. rather than exterminate the population. Smith, M. 2000. The Hornet robberfl y (Asilus crabroniformis): land use and livestock grazing regimes at sites in England. English Nature Management for Woodlarks should benefi t Hornet Research Reports No. 387 robberfl ies where this maintains mosaics of bare Stubbs, A. E. & Drake, M. 2001. British Soldierfl ies and their allies. An illustrated guide to their identifi cation and ecology. ground and different sward heights on heathland or British Entomological and Natural History Society, Reading. in woodland clearings and light stocking rates on Larger Brachycera Recording Scheme: low input pasture or the accommodation of rabbit Biological Records Centre www.brc.ac.uk populations. The ELS and HLS options chosen for The Dipterists’ Forum www.dipteristsforum.org.uk

Buglife – The Invertebrate Conservation Trust Registered in England at First Floor, 90 Bridge Street, Peterborough, PE1 1DY. Company no. 4132695. Registered charity no. 1092293. Scottish charity no. SC040004 First Floor, 90 Bridge Street, Peterborough, PE1 1DY Photography. © Cecile Bassaglia; eating © Neil Phillips Telephone: 01733 201210 Email: [email protected] Acknowledgements: Simon Hayhow - Larger Brachyptera Recorder; Alan Stubbs - Diptera Expert; Mike Howe - Countryside Council for Wales; the Dipterists Forum www.buglife.org.uk This leafl et has been sponsored by the Department for Environment, Food and Rural Affairs.

7/2010