Rewilding and spiders

Posted by Graeme Lyons , Friday, 13 October 2017 12:48

Butcherlands is a small (c80ha) series of fields adjacent to Ebernoe Common which were in arable until 2001. The site boasts some thick hedgerows but lacks veteran trees. It sits on Wealden clay so is very wet in the winter and the vegetation is neutral to slightly acidic in places. Sussex Wildlife Trust mainly manage Butcherlands by 'pulse-grazing', that is only grazing part of the year, say backing off with heavy grazing over the summer and moving animals back in in the winter for  a harder graze. We do not always stick to this plan though, in some years grazing a part of it harder and in other years not. We have maintained a network of fences and gates that allows for this flexibility. Fences act like predators by forcing animals to move around the site, it's vital that we keep them. 

We are also moving towards breaching one of our 'limits of acceptable change' when it comes to the amount of bramble cover present and so will intervene mechanically to control this. Grazing of woody vegetation by the livestock we have available is simply never going to control this plant and so a compromise has to be made or else we will lose the species-rich and invertebrate-rich grassland we have created over the past 16 years.

Which brings me to the invertebrate survey that Mike Edwards and I have been doing this year. We just finished the last visit to the site on the 9th October. Pretty late in the year but a good visit none-the-less. This also ends my season of terrestrial invertebrate survey field work! Wahoo! Anyway, I still have many jars of beetles to identify and all of Mike's records to add to the species list but my list currently stands at 447 species for the site. The one taxa I have completed is the spiders and that's what I am going to write about here.

I have been struck as I carried out this survey by how rich the spider assemblage is here considering it was arable only 16 years ago. Ebernoe Common is our second most speciose reserve (we count Butcherlands as part of Ebernoe), it's just gone over the 3800 species mark. It's actually Butcherlands that's pushed it over. You could say that the spiders have simply colonised from Ebernoe but many of these are species that have never been recorded on Ebernoe before. A total of 73 species were recorded on the survey of which 7 (or 9.6%) have conservation status. This is really high and really respectable for spiders on a nature reserve, one of the highest I have seen away from places like Iping and Rye Harbour (heathlands and coastal sites basically). So what's going on? Well, I believe it's all about the sympathetic structure provided by the pulse-grazing. It produces plenty of structural types in the sward that cannot be provided by all year round steady state grazing. In addition, plenty of structure is also being provided by the developing woody vegetation but as you will see this does not provide much of the habitat for the scarcer species.

The survey took the form of six visits. On each visit, the seven main fields were visited for half an hour each and the methods appropriate to the season were used to record invertebrates. These seven species lists were then bulked over the survey period giving a species list for each field and for the whole site. The order they were carried out in was varied. So here are the seven species lists. The conservation status is shown after the species name as being either Nationally Scarce (NS) or Nationally Rare (NR).

  Brick Nine Hill Church Lime High Spark
Species 1 2 3 4 5 6 7
Achaearanea simulans 1            
Agalenatea redii 1 1 1 1 1 1 1
Agelena labyrinthica 1 1 1 1 1 1 1
Anelosimus vittatus 1 1 1 1 1 1 1
Anyphaena accentuata             1
Araneus diadematus   1   1   1 1
Araneus quadratus 1 1       1 1
Araniella cucurbitina   1   1 1    
Araniella opisthographa     1        
Argiope bruennichi     1 1      
Bathyphantes gracilis     1        
Ceratinopsis stativa     1        
Cercidia prominens (NS)         1    
Clubiona brevipes     1 1      
Clubiona diversa   1          
Clubiona reclusa 1            
Clubiona subtilis 1            
Cyclosa conica           1  
Dictyna arundinacea 1 1 1 1 1 1 1
Dicymbium brevisetosum             1
Erigone atra 1 1 1   1 1  
Erigone dentipalpis   1 1 1 1    
Ero cambridgei 1 1 1     1 1
Ero furcata           1  
Evarcha arcuata (NS) 1   1 1   1  
Gibbaranea gibbosa 1           1
Heliophanus flavipes             1
Hylyphantes graminicola   1          
Hypsosinga pygmaea 1 1 1 1 1 1 1
Hyptiotes paradoxus (NS)             1
Lariniodes cornutus 1 1 1 1 1 1 1
Lathys humilis     1        
Linyphia hortensis         1    
Linyphia triangularis         1    
Mangora acalypha 1 1 1 1 1 1 1
Marpissa muscosa (NS)   1 1 1     1
Metellina mengei 1 1   1 1 1 1
Metellina segmentata       1   1  
Misumena vatia   1 1 1      
Neoscona adianta 1 1 1 1 1    
Neottiura bimaculata         1    
Neriene clathrata   1 1 1   1  
Ozyptila brevipes     1 1   1  
Ozytila simplex           1  
Pachygnatha clerkii     1 1 1    
Pachygnatha degeeri 1 1 1 1 1 1 1
Padiscura pallens       1      
Pardosa amentata 1            
Pardosa nigriceps         1    
Pardosa paludicola (NR)   1 1        
Pardosa pullata         1 1  
Pelecopsis parallela   1          
Philodromus aereolus         1    
Philodromus albidus 1       1   1
Philodromus praedatus           1  
Phylloneta impressa   1 1        
Phylloneta sisyphia   1 1   1 1  
Pisaura mirabilis 1 1 1 1 1 1 1
Platnickina tincta           1 1
Robertus arundineti 1            
Sibianor aurocinctus (NS) 1   1 1 1    
Tallusia experta         1 1 1
Tenuiphantes flavipes         1    
Tenuiphantes tenuis 1 1 1 1 1 1 1
Tetragnatha nigrita       1      
Tibellus oblongus 1   1 1 1 1  
Trematocpehalus cristatus (NS) 1       1    
Trichopternoides thorelli           1  
Walckaeneria antica 1     1 1    
Xysticus cristatus 1 1 1 1     1
Xysticus lanio           1  
Zilla diodia     1     1  
Zora spinimana 1     1 1 1 1
TOTAL 29 28 33 31 32 32 25
Total spp. with cons status 3 2 4 3 3 1 2
%age spp. with cons status 10.3 7.1 12.1 9.7 9.4 3.1 8
So Hilland came out on tops and this has mostly been reflected in other taxa across the site. It sits a little higher than the rest and is more free draining (slightly sandier too) and this may explain it. Of these 73 species, only 10 (13.7%) were recorded in all seven fields while 31 species (42.4% were recorded in one field only (these are known as 'unique' species). This fairly typical for a survey of this type and shows just how hard it is to thoroughly survey a site as well as how some species naturally occur at such very low densities.

The seven scarcer species are as follows:

Cercidia prominens (NS). Only one of these beautiful spiders was found, an adult male during the October visit (photo of which is at the top of this blog). Found on Common Fleabane in Limekiln Field. I have previously only seen this on heathland and once on chalk downland. It was new to Ebernoe as well as Butcherlands. A species here associated with the grassland rather than the woody component.

Evarcha arcuata (NS). Before I started this survey I regularly would see this jumping spider at Butcherlands (especially in longer grass at Hilland). At this point it was new to Ebernoe Common. This species is abundant on the west Sussex Heaths. I have never seen it anywhere away from Heather except here at Butcherlands. I've also never heard of anyone else finding it  away from heathland so it's interesting what it's doing here so well established yet so far from heath. It's sandier here but a long way from being acid grassland. This survey proved it was widespread turning up in four of the seven fields. A species here associated with the grassland rather than the woody component.

Hyptiotes paradoxus (NS). I was amazed to find I had swept an immature one of these incredible spiders from Juncus in Sparkes Field! Nothing like what the text say it likes. This is only the second time I have seen this spider and only the first time I have seen it in Sussex. In fact this spider would have been a first for west Sussex if I had encountered it three days earlier (it was recorded at Kingley Vale). It was new to ALL Sussex Wildlife trust reserves not just Ebernoe. Although I encountered this in the grassland, it is known for being more arboreal.

Marpissa muscosa (NS). Our largest jumping spider was already well recorded from Ebernoe and is strictly not a grassland species. It's not all that scarce in Sussex, we get it in the kitchen at work! Rather this specie favours old trees and gate posts, especially if they are in the sun. In fact, it was on the gate posts that this species was more often recorded. It was recorded in four of the seven fields.

Pardosa paludicola (NR). The star of the show. By far. This massive blackish wolf spider was a totally unexpected find. It's only known from a few sites and was only the second record for Sussex (it turned up only two miles from here many years ago). In fact it's so are it hadn't even been recorded in the UK since 2004! This species is clearly an early successional species and would not do well here if it all went to scrub. So was it always here or has it moved in? (Photo above by Evan Jones). It occurs in two adjacent fields in a wet area not huge in extent and it was abundant in both those fields.

Sibianor aurocinctus (NS). This little grassland spider seems to be turning up much more frequently. I only recorded it for the first time last year but since then i have recorded it quite a few times. In this survey it was recorded in four of the seven fields and always in the grassland. Again dense blocks of scrub and woodland would not benefit this species. It was new to Ebernoe Common during this survey.

Trematocephalus cristatus (NS). This small but highly distinctive money spider was the only money spider of the survey to have conservation status and was recorded in two fields. An arboreal species already common in Ebernoe, it would also do well in a more woody dominated system not requiring a sward at all it would seem. However I have always found more of them on the edge of woodland so a mosaic of woodland, scrub and grass would be ideal.

Which is precisely what we are trying to achieve here at Butcherlands. So can you say rewilding is good for spiders? I don't think that would be fair, I haven't seen similar results at other sites where heavier grazing produces a less desirable sward for spiders. I think it's fairer to say that sympathetic and pulsed conservation grazing and the application of natural process is what's worked here. Would you call that rewilding? Many would but I see the human intervention of pulsing the grazing is what's worked here to produce a rich and varied structure so vital for spiders and many other invertebrate groups. Some might not call that rewilding but I think it's really important that we do and don't adopt a purist 'all or nothing' approach to it. It's important that we don't get tied up in semantics. 

The key thing here is to monitor and continuously adjust the management so that the grazing and the natural processes we apply (or their analogues when a more natural tool isn't available - such as the planned bramble cutting) are the best they can possibly be for wildlife. We have created some wonderful species-rich grassland here and it would be unfair to allow it to drift entirely into a scrub dominated system (and then eventually woodland) just because rewilding is the main approach to management. And that is what would happen with the livestock we have available, make no mistake. As far as I am concerned, this is the only way rewilding can ever work as a part of conservation, otherwise we are simply blindly walking into the dark being lead only by our own confirmation bias.

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