Notes on Walckenaeria stylifrons

From The Newsletter No. 77 November 1996

The linyphiid spider Walckenaeria stylifrons was described as new to Britain from material collected at Weeting Heath N.N.R., Norfolk (Nat. Grid Ref. TL 7689) in 1963 by Eric Duffey (Duffey & Denis, 1967). He collected two females and two males from pitfall traps set in March and April. Weeting Heath was at that time characterised by a tall, dense, uniform grass turf (consisting mainly of Red Fescue, Festuca rubra L., and Sheep's Fescue, F. ovina L.) which had developed following the decline of rabbit numbers following the arrival of myxomatosis at the site in 1954/5. Duffey and Denis (1967) also reviewed the available European distribution and habitat information for W. stylifrons and found that most records were from dry places, on light, usually sandy soil, near the coast.

In the spring of 1989, Andy and I began an opportunistic piece of research to investigate the invertebrate fauna of a part of Weeting Heath. An experimental plot was established to find out how best to produce the disturbed ground favoured as a breeding site by the Stone Curlew and to produce the right conditions to encourage characteristic breckland plants (see Dolman & Sutherland, 1992, 1994). This part of the reserve is fenced to keep the rabbits in and therefore has a short, springy turf. The study area, prior to treatment, was dominated by Red Fescue (F. rubra), Spreading Meadow Grass (Poa humilis Ehrh. ex Hoffm.) and creeping mosses.

The experiment was set up following a stratified random block design with four replicates of three treatments and a control. Each block was a strip of about 40 m by 20 m. The treatments were: ploughing, rotavating and forage harvesting. In the spring of 1990, the ploughed and rotavated plots were sub-divided longitudinally and one subdivision in each plot rotavated.

Pitfall traps were set within each of the plots, one near each end of a strip. Each treatment therefore had eight traps associated with it. The traps were plastic cups set into a second cup that acted as a sleeve, so that when the traps were emptied the area was disturbed as little as possible. The trapping fluid was ethylene glycol-based antifreeze. Each trap had a tin can lid propped above it (a) to stop any small vertebrates from drowning; and (b) to stop the traps filling with rain water. The traps were run more or less continuously from spring 1989 to autumn 1991 by Andy and me, and then by myself alone until the summer of 1994.

The first few thousand spiders identified by the end of 1992 yielded no W. stylifrons. When I was able to get back to the material, I decided to concentrate on the early season samples likely to contain the spider. At last one female was identified from a strip that had been forage harvested (SI), from a trap that ran from 23rd March to 4th August 1989. The long trapping period covered the nesting period of the Stone Curlew when we were banned from the site. A second individual, a male this time, was recovered from a trap in place between 6th and 13th March 1994 and set in a strip that had been rotavated in both 1989 and 1990 (S2). The vegetation height at SI was about 3 cm, and at S2 about 1 cm. As might be expected, S2 had a high percentage of bare ground; a little over 50 per cent. So far then my two specimens have come from short or very short grassland; Eric Duffey's four came from relatively tall thick grass. I have just begun to look through the literature to see if any further micro-habitat clues are forthcoming. I also posted a request for information to the arachnology list on the internet and got a reply from Dr Rudy Jocque who found W. stylifrons in very short grassland behind a dune system on the Belgian coast.

I still have a lot of material to work through, including samples taken from another part of the site with areas of longer grass. It will be interesting to see how many more individuals turn up and in what habitats. As W. stylifrons is still only known in Britain from Weeting Heath, it is important to try to determine whether any particular treatment favours or prejudices survival of this species.

References
Dolman, R M. & Sutherland, W. J. (1992) The ecological changes of Breckland grass heaths and the consequences of management. J. appl. Ecol. 29: 402-413.
Dolman, R M. & Sutherland, W. J. (1994) The use of soil disturbance in the management of Breckland grass heaths for nature conservation. J. Environ. Man. 41: 123-140.
Duffey, E. & Denis, J. (1967) Wideria stylifrons (O.R-C.) a southern European spider from the Norfolk breckland. Trans. Nor/. Nor. Nat. Soc. 21: 25-31.
 
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