LOWLAND HEATHLAND - SPIDER-HUNTING WASPS
(Pepsini 2 - Dipogon)
There are portraits of the male of the species and the habitual prey, the crab spider Xysticus cristatus, in the Homes & Gardens section but Dipogon variegatus can be found in plenty of other habitats including heathland.
The wasps shown on this page were all photographed on two adjacent root-plates, including the one shown on the introductory page for spider-hunting wasps, between June and September 2006, but nests are created in various pre-existing cavities, including holes in the ground, snail shells, borings in timber and walls.
In late September 2006 one even created a nest in an Odynerus spinipes burrow (see the Sandpits section for details of that wasp) that had been active earlier in the year. Hardly a promising location, since there was no guarantee the adult Dipogon variegatus would be ready to emerge before the other residents started coming out.
The nests may contain several cells or just one and partitions are made of specks of soil, or fair-sized lumps, carried in the mandibles and on bristle tufts found on the wasp’s jaw. These bristles, a characteristic unique to Dipogon species among the spider-hunting wasps in Britain, are also useful for excavating from the burrow to make it shipshape. This is normally performed with remarkable rapidity – one female spent 40 minutes pulling out a few grains of sand every eight seconds, amounting to more than 300 extractions.
The method of transporting prey can be a trifle haphazard. The spider is always grasped by the spinnerets but may be dragged or carried in front, depending on its size. The exceptional wasp on this page is the one shown in the second, fourth, fifth and sixth images. She was the largest at 11mm (larger than most text-books state) and not only carried the spider forwards most of the time – she also flew for at least a metre on to the root-plate with the spider grasped in her mandibles. As a bonus, she allowed a view of egg laying.
Flying with prey is not that common among spider-hunting wasps, but I noticed four species doing this in 2005 and 2006. Besides Dipogon variegatus, which to my knowledge had not been seen behaving in this manner previously, they were Agenioideus cinctellus, Auplopus carbonarius and Episyron rufipes.
On top of that, some species take short jumps with prey in the mandibles, including one small Priocnemis species which I didn’t manage to identify. More observation may reveal more examples of this behaviour, though as the group has been pretty closely observed over the last century new findings are unlikely to be everyday occurrences.
Returning to more ‘ordinary’ activities, the route taken by Dipogon variegatus with prey is not necessarily direct – three females pulled their prey up and down grass stems for no apparent reason, and another took her spider a total of two metres up and then partially down the root-plate to reach her nest. The straight route was just over a metre.
Another female went up more than a metre diagonally, then dropped to the ground with the Xysticus cristatus still in her mouth – the grip of this species is as strong as any I’ve seen. The fall took her past the burrow entrance, whereupon she climbed straight up, with no deviations, and into the burrow. How much of this was by design and how much accidental is incalculable.
The toughest assignment was hauling a spider up an unstable sandy slop at the bottom of the root-plate, which took one wasp 20 minutes. Then came a 70cm climb up a vertical face. All told the wasp was engaged for 45 minutes before the spider was safely interred, pulled in backwards as is the norm.
Once the nest is complete, Dipogon variegatus closes it off and theoretically makes it safe with a felt-style barrier constructed partly of old spiders’ webs, with or without earth attached, which are garnered from nearby and ferried for the purpose.
Theoretically is the word, though, given the presence of a number of the ruby-tail wasp Trichrysis cyanea on the root-plates. These, which are noted for parasitising spider-catching Trypoxylon wasps, kept investigating the burrows and eventually a female entered one with her ovipositor clearly extended – this can be made out on the image. (Ruby-tail wasp females all have this ‘telescopic’ arrangement of the tip of the abdomen, which stays concealed except when egg laying. This characteristic is unique to them among Hymenoptera.)
The Trichrysis cyanea was inside for nearly three minutes, and the web barrier was loosened to enable her to lay the eggs. On her return, the Dipogon variegatus detected a change, but rather than abandoning the nest as a lost cause she removed the web and started refilling the burrow, finally sealing it as if nothing was wrong.
Apart from a record abroad, there seems no other mention of Trichrysis cyanea going after a spider-hunting wasp nest, so this was a fortunate observation. Not so fortunate for the offspring of the Dipogon variegatus, of course.
Images © Jeremy Early. All rights reserved.
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