All three British Crabro species are found in the sandpit owing to its having a 45-degree slope of both friable and compacted sand. While two (cribrarius and peltarius) are common, scutellatus is nationally scarce.
They all prey on flies, and vary in size from 16mm (Crabro cribrarius) down to 10mm (Crabro peltarius), though there can be considerable differences even within one species at one site. Some of the Crabro peltarius at the sandpit were around 14mm. The pictured Crabro cribrarius was photographed elsewhere,
Rarely for solitary wasps, the males are often at least as big as the females. For reasons that are obscure, but which are echoed elsewhere in the world of invertebrates including with beetles, males have an enlarged fore tibia, carrying what looks like a shield. This is an easy distinction from all our other wasps.
Crabro species' method of hunting seems a bit hit and miss, since they dive at speed, aiming to collect a fly in their forelegs and immediately take off.
Observations of Crabro peltarius hunting fairly small flies on a sunny bank over several days revealed one strike from every two or three dives, and frequent readjustment to get the prey in the right position for flying back to the nest. Given that they can require over 60 flies to stock the nest, this is a major commitment of time and effort. As the image above shows, though, much larger prey can be caught. Up to a point it depends on the size of the predator.
The nests for all three species tend to be fairly long and in inverse proportion to their size - up to 28cm for peltarius and 20cm for cribrarius. Crabo scutellatus is more restricted in prey than the other two, since they catch almost entirely Dolichopodidae flies found in the vicinity of water.
There are more than 20 species of Crossocerus wasps in Britain, requiring a wide range of invertebrates for their larvae to feed on.
Crossocerus quadrimaculatus (10mm), one of the largest and commonest, is seen from July to September and preys mainly on flies. It is in a minority in the group in nesting in open, sandy situations and is exceptional in having two colour forms, pale and dark, which can co-habit. Males tend to have much less yellow on them. At 6mm Crossocerus tarsatus is one of the smallest members of the genus. The equally tiny Crossocerus ovalis is not quite so common and specialises in sandy soil.
Lindenius panzeri (6mm) is shown mating 'head on' on the Solitary Wasps page in the main Heathland section. The species, which preys on Chloropid flies, is suited by compacted soil, a commodity in short supply in the pit, where most of the sand is friable. There is enough, though, to provide for the wasp, which doesn't need that much space. Intriguingly, the female pictured above with prey alongside had a dickens of a job excavating her burrow - after half an hour she was only 1cm or so into the ground, at which rate it would have taken hours to do the job.
Similar in appearance but preying on small adult beetles is Entomognathus brevis (6mm), which is ideally suited by the type of sandy slope found at the pit. They are pretty common and construct up to ten cells per nest, with an average of 20 beetles stored in each cell. The larva covers its cocoon with sand grains.
If prizes were awarded to Hymenoptera, Oxybelus uniglumis would be a prime candidate for top honours. They are among the fastest hunters in the business, with an observer decades ago timing six flies caught in five minutes. The wasp in the first two images alongside caught five in six minutes at the sandpit. By expert observation elsewhere, the burrow of up to 12cm can be dug in two hours or so with two or three cells and up to 16 flies then placed in each cell.
A female can dig and complete more than one nest each day, this despite the time added on by taking the trouble to cover the entrance whenever the wasp goes hunting.
Clearly this exponent of life in the fast lane shows remarkable efficiency and strength, along with a phenomenal ability to generate sufficient poison for the job in hand - even though the flies are paralysed with only one sting, there are still an awful lot of stings required for each nest.
Moreover, the prey, after being carried back to within a metre or so of the burrow by the female, uniquely is then deposited briefly and impaled on the sting before being carted into the nest forwards.
Perhaps the prize for astonishing carriage goes to the second Oxybelus uniglumis pictured, with a greenbottle. Unsurprisingly she found it hard work flying with such bulk beneath, tending to keep low, but managed it all the same for some quite some distance. This perhaps confirmed that aerodynamically, invertebrates are among the most intriguing of all creatures, with wasps and their prey in pole position. If they are not studied closely by humans in the military or civilian spheres, they should be. (Another example of a massive payload is Astata boops, which also nests in the sandpit.)
Oxybelus uniglumis is one of three from the genus found in Britain. The other two are much less common. Oxybelus argentatus is shown on the Coast pages, a habitat which is also ideal for Oxybelus mandibularis (7mm). Both of these also catch Diptera.
For all its strength and dynamism, Oxybelus uniglumis doesn't have everything its own way. Their nests can be parasitised by Myrmosa atra (6mm), or the Black-headed Velvet Ant, which looks like an ant but is a wasp and preys on a wide variety of hosts. Males are winged but females are flightless and the species is believed to be a parasitoid, feeding on the larva rather than the food provided for it.
In another remarkable example of the power of ants, an Oxybelus uniglumis which appeared to have been stunned by some event was collected by a worker ant and carted for more than a metre across the sand to the nest while still vainly struggling to escape. Proof that, as always in nature, even the biter can be bit.
As an aside, empty burrows of one sort or another sometimes are used by male wasps for shelter overnight or if rain arrives. The commonest species doing this at the sandpit have been Ectemnius continuus and Cerceris rybyensis, neither of which nests in vertical sand banks. Ectemnius continuus is a wood-nesting species while Cerceris rybyensis goes for level sand. There can be face-offs between the males, as the image above shows. The 'sitting tenant' is invariably the one to come out on top, predictably given the inability of the latecomer to exert any threat.
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.