Robberflies (Asilidae) of the Sefton Coast sand-dunes

Asilids are insects with attitude. They are active predators of other insects and therefore have good eyesight and rapid reactions, making them challenging subjects for photography. This is a small family as insects go with only 28 species known to occur in Britain. However, several have a southern or south-eastern distribution or are confined to Scotland and are unlikely to appear on the Sefton Coast. Robberflies show a preference for dry, well-drained soils and a warm climate, so coastal dunes are a favoured habitat, though some species are associated with woodland or woodland edge.

Stubbs & Drake (2014) give detailed accounts of all the British asilids, while Brighton (2017) provides check-lists for vice counties 58 (Cheshire) (14 species), 59 (South Lancashire) (9 species) and 60 (West Lancashire) (10 species), as well as supporting information on the status of robberflies in the Northwest.

Brighton (2017) mentions that five species have been added to the Lancashire and Cheshire list since 1970: Dioctria linearis, Leptarthrus brevirostris, Machimus cowini, M. atricapillus and Pamponerus germanicus¸ these being fairly modest expansion of known ranges. M. cowini was confined to eastern Ireland and the Isle of Man until recorded in south Cumbria in 2006. Several more specimens were found on the east side of Morecambe Bay in July 2013. A species of large coastal dune systems, Pamponerus germanicus, had been strangely absent from the Sefton Coast until one specimen was recorded in 2000. However, no more of this distinctive species has come to light. Leptogaster cylindrica was considered rare in the region until relatively recently but has become one of the commonest asilids, though not, as yet, recorded on the Sefton Coast. A fairly widespread species in England occurring in a range of habitat types, Dioctria atricapilla has two Sefton Coast records but has not yet been found by us. D. rufipes is also widespread in England and Wales, including in Wirral and the Fylde, but there are no sightings recorded for the Sefton dunes.

In recent years, we have photographed six robberflies on the Sefton dunes (discussed below). Other species that could turn up are P. germanicus (Pied-winged Robberfly), L. cylindrica (Striped Slender Robberfly), D. rufipes (Common Red-legged Robberfly) and D. atricapilla (Violet Black-legged Robberfly). M. cowini (Irish Robberfly) seems unlikely but may be a possibility.

Machimus cingulatus/M. atricapillus (Brown Heath/Kite-tailed Robberfly)

These two medium-sized robberflies with orange patches on the legs are difficult to separate. A putative example was found at Ainsdale Sand Dunes National Nature Reserve (NRR) in August 2017 (Fig. 1).

M. cingulatus is widespread but sporadic in England and Wales, becoming rare north to Scotland and coastal in the north and west. It favours sandy heaths and dunes. There is one previous record for the Sefton Coast. Although widespread in England, M. atricapillus has not been recorded for VC58, 59 and 60. It is associated with a wide range of open habitats on dry soils.

Figure 1. Putative female Machimus sp., Ainsdale NNR, August 2017

Dysmachus trigonus (Fan-bristled Robberfly)

This distinctively hairy robberfly (Fig. 2) is a fairly familiar sight in the Sefton dune system, being the second commonest species after Philonicus albiceps. It is widespread in England and Wales, becoming mainly coastal in the north and associated especially with fixed-dunes, pathways and adjacent grasslands.

Figure 2. Dysmachus trigonus Ainsdale NNR, June 2019

Philonicus albiceps Dune Robberfly

The most characteristic of sand-dune robberflies, this large greyish insect with black legs (Fig. 3) can be found throughout the summer on warm sandy patches and footpaths in the outer dunes, often sharing its habitat with the Northern Dune Tiger Beetle (Cicindela hybrida). P. albiceps’ prey consists mainly of other flies, often relatively robust species. This species is often abundant on coastal dunes throughout England and Wales, as far north as central Scotland.

Figure 3. Philonicus albiceps pair, Ainsdale Sandhills LNR, August 2019

Leptarthrus brevirostris Slender-footed Robberfly

A female of this rather distinctive, robust asilid (Fig. 4) was an unexpected find by PK in June 2019 on a firebreak in Ainsdale NNR. It is widespread, though local, in much of England, though NBN Atlas shows no records for VC58 (Cheshire) and VC59 (South Lancashire, including the Sefton Coast and it is not listed for VC59 by Brighton (2017). In south and central England it is mainly associated with chalk and limestone grasslands but may sometimes be found near to springs or pools. Further north and west, more acidic and wooded habitats are used.

Figure 4. Female Leptarthrus brevirostris Ainsdale NNR, June 2019

Dioctria baumhaueri Stripe-legged Robberfly

A rather small, slender robberfly, this species is mostly black but the front and mid-femora are extensively orange below (Fig. 5 & 6). It is widespread in England and Wales but nbn gateway shows only two Sefton Coast records. A female was photographed on Range Lane, Formby on 1^st July 2019. This insect is particularly associated with woodland edges and broad-leaved shrubs.

Figure 5. Dioctria baumhaueri Range Lane, Formby, July 2019

Lasiopogon cinctus Spring Heath Robberfly

This small but robust robberfly is mostly black with yellowish dusting on the sides of the thorax; the legs are completely black (Fig. 6). Being nationally scarce, it is mostly found on southern heathlands, being more sporadic and mainly coastal further north to Cumbria. The habitat is sandy heaths and dunes. One was spotted by Paul Brock during a visit to Birkdale Green Beach on 14th May 2019. NBN Atlas has five Sefton Coast records.