LOWLAND HEATHLAND - SPIDER-HUNTING WASPS
(Pepsini 3 - Cryptocheilus)
Cryptocheilus notatus is the largest of all the British spider-hunting wasps (Pompilidae), measuring up to 18mm, and the species was also one of ten Pompilids in our list included in the Red Data Book of 1987.
That figure was revised provisionally to seven in 1991, when Cryptocheilus notatus was one of only two be ‘upgraded’, from RDB3 to RDB2. At that stage this impressive wasp had been seen almost entirely in Dorset and points westward since 1970, but happily matters have improved dramatically over the last couple of decades, with the west Surrey heaths one of the new areas providing a significant number of sightings.
Cryptocheilus notatus, which requires warm situations fully exposed to the sun, can no longer strictly be described as under threat, though it is still local. Hotter summers, plus the increased management of and protection afforded to heathland and coastal dunes, together with the wasp’s ability to fly powerfully, have almost certainly contributed to the increase in range.
A typical, albeit small, site where the species is to be found in reasonable numbers from July to September is a disused sandpit at Frensham Common in Surrey, where a sheer face measuring 3.5 metres high by 10 metres wide facing south-west provides a warm micro-climate. There is open sand in front of the face, with plentiful Heather beyond that.
Like Auplopus carbonarius but unlike the vast majority of Pompilids, Cryptocheilus notatus constructs multi-celled nests. Understandably, given the size of the wasp and the prey caught, they require quite substantial pre-existing cavities – there is no major excavation by the wasp.
In Europe sites have included mammal burrows, notably those of Moles (Talpa europaea), but the observed wasp at Frensham used a disused invertebrate nest site, presumably expanded.
How often nesting burrows are as far off the ground as with this female is a matter for debate. She was spotted with prey a metre from the foot of the cliff on loose, sloping sand. The victim was Drassodes cupreus (18mm), a large ground spider from the Gnaphosidae family which hunts nocturnally.
For about ten minutes the Cryptocheilus notatus attempted to transport her prey to the bottom of the cliff but with little traction the job proved all but impossible. She left the prey several times and had great difficulty finding it on her return – as with Anoplius nigerrimus, orientation seems underdeveloped with Cryptocheilus notatus.
Eventually the spider was left, seemingly for good since there was no sign of its captor for ten minutes. I collected it to effect identification, whereupon the Cryptocheilus notatus returned. The spider was placed back on the ground nearer the cliff face, and the wasp found it, albeit not immediately.
The difference between the firm vertical part of the pit and the soft sand in front for ease of movement was illustrated perfectly over the next few minutes as the wasp moved to the foot of the cliff and started moving up, going backwards with the spider held near the head. The route, as shown in the accompanying image, was diagonal including two small troublesome sections of loose sand and a little patch of Heather, which for some reason was wandered over extensively.
After four minutes the Cryptocheilus notatus reached the top of the pit, only to set off downwards immediately, with the spider in front – gravity forced this action on her. Within a minute the wasp had reached its burrow and pulled the spider in.
The distance traversed by the Cryptocheilus notatus amounted to around five metres, virtually all on a sheer face. Given the habits of the species, this female might have carried out the same performance several times before her death, an astonishing testimony to her strength and agility.
Images © Jeremy Early. All rights reserved.
In 2013 I published My Side of the Fence – the Natural History of a Surrey Garden. Details may be found, and orders placed, via this hyperlink My Side of the Fence. In November 2015 Surrey Wildlife Trust published the atlas Soldierflies, their allies and Conopidae of Surrey, jointly written by David Baldock and me. Details are on this web page: Atlas.