LOWLAND HEATHLAND - SPIDER-HUNTING WASPS
(Pompilinae: Arachnospila spp)
Arachnospila anceps (11mm) is the largest and commonest of four species in the Ammosphex subgenus and the female resembles Anoplius infuscatus, using the same method of storing prey on low vegetation. Prey comes from a wide range of spiders.
Arachnospila anceps are found from May to October. The female with prey was photographed on October 16, later than the species generally is acknowledged to be active but, given milder autumns and the continuing presence of prey, there is no reason why they should not remain busy.
They burrow swiftly at an angle up to a depth of five centimetres, using the mandibles, and the prey carriage is backwards. As with Anoplius nigerrimus, Arachnospila anceps appear sometimes to forget where they have deposited prey if it is left en route to the nest site, without any alteration being effected to the locale.
Arachnospila trivialis (9mm) is very similar to anceps. The two species can be found together, as generally they show the same behaviour and require the same sort of habitat, although trivialis is found more often in coastal areas.
One possible difference between the two species is that Arachnospila trivialis is noted in earlier records, as in my picture above, pulling its prey using the spider’s spinnerets. The second wasp, shown hauling the prey into the burrow on a bonfire site, did the same. This doesn’t mean that transportation always occurs in such a manner, and Arachnospila anceps may well sometimes use the spinnerets. However, in a fair number of viewings of prey movement, I’ve never seen it do so; the point of contact invariably has been between the thorax and abdomen.
As a point of interest, the prey of the second Arachnospila trivialis above was a male spider. No distinction is drawn between the sexes as regards their usefulness as food for the larva, and the solitary wasp Cerceris rybyensis offers another instance of a species that catches its share of each sex.
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.