Asilus crabroniformis (Diptera: Asilidae) Hornet Robber-fly at the Devil's Spittleful NR, Kidderminster
On 25 August 2011 whilst looking for invertebrates on the Devil's Spitleful my attention was drawn to a loud distinctive buzzing and I immediately realised it must be Asilus crabroniformis. Within seconds a large orange fly was spotted setting down onto some fresh cattle dung and the identification was confirmed. As far as I am aware this is the first record of A. craboniformis from this location. For many years (over 50?) the site has not been grazed so the availability of dung (and associated dung invertebrates) would have been restricted to wild animals such as rabbits. At least two flies were noted both actively searching around the fresh cattle dung, one individual flew up in an arcing flight to take insect prey in mid-air, which was later identified as an Onthophagus spp. Beetle (Fig. 1.).
In Worcestershire the adult fly was first found by Brett Westwood during 1995 (Westwood1997) inhabiting a pony pasture on the edge of Kidderminster. Despite searching this year I found none at the former Kidderminster sites but Mike Averill has reported seeing one. (Averill pers.comm.) The species is of considerable local importance and listed as nationally notable (scarce) on the priority list of the national Biodiversity Action Plan (UK Steering Group 1995) and well documented locally by David Green in the Worcestershire Record. (Green 1998 & 1999).
It is pleasing to see this species on a protected site and Worcestershire Wildlife Trust Reserve Manager Andy Harris is aware of the species presence. Thankfully the grazing animals (Shetland cattle) are part of the Wyre Forest Grazing Animals Project and ivermectins used as antiparasitic digestion treatments are not used on site (only used in winter back on the owner’s farm) (Harris. pers. comm.). This means the dung can be utilised by beetles and other invertebrates so providing food for the adults and larvae of Asilus. Now that Asilus has been noted here it is hoped that the grazing of cattle can be established as a regular late summer activity as part of the management of this heathland site. Part of the same herd of cattle graze Wilden Marsh NR, Near Kidderminster, but so far despite searching Asilus crabroniformis has not been seen at this location, possibly the habitat is unsuitable.
Westwood, B. 1997. Pats and Robbers. Worcestershire Record, 3:7
Green, D.M. 1998. Asilus crabroniformis L. Hornet Robber Fly. Worcestershire Record, 5:10
Green, D.M. 1999. Asilus crabroniformis (Diptera - Asilidae) in Worcestershire, Kidderminster Area, 1999. Worcestershire Record, 7:12.
Fig. 1. Asilus crabroniformis, Hornet Robber-fly, with Onthophagus beetle. John Bingham