notes on the suffolk list of coleoptera: 7 the genus ischnomera stephens (oedemeridae)

95 SPIDERS OF RAF MILDENHALL

Trans. Suffolk Nat. Soc. 36 (2000)

THE SPIDERS OF RAF MILDENHALL

PAUL LEE

Land utilised by the military for several decades or more may support areas of relict habitat which have been lost from the surrounding countryside through agricultural and development pressures. In this way, fragments of semi-natural breckland, which may otherwise have been ploughed up or disappeared under concrete, have been preserved through the establishment of air bases on the Suffolk Brecks during the 1920s. At RAF Lakenheath the value of this habitat is recognised by the designation of the airfield as a Site of Special Scientific Interest. Although there has been little work on the invertebrates of the SSSI, the results of a survey by English Nature suggest the fauna may be very rich (Key, Drake, Sheppard & Procter, 1992). At RAF Mildenhall similar habitats exist but the airfield is not a SSSI and is better known for air shows than natural history. However, recent work suggests that the invertebrate fauna is at least as diverse as that of RAF Lakenheath and includes a number of nationally important species (Lee & Suffolk Moth Group, 1999). In this paper the arachnological component of this invertebrate fauna is discussed and compared with that from other sites in Suffolk.

Survey methods At the end of 1998 I was contracted by SWT Trading Ltd to undertake a preliminary survey of a number of invertebrate groups, including spiders, on the USAF base at RAF Mildenhall. This was followed by a more complete survey of the site between May and November 1999. As a result of the preliminary survey six sites were selected for detailed investigation in 1999. Habitat descriptions and grid references for these sites are given in Table 1. At each location a line of five pitfall traps was set in May 1999 (July in site 6) and emptied at monthly intervals until November. These habitats and a number of others around the air base were also sampled using hand-collecting techniques, sweep netting and / or beating as appropriate and vacuum samples were taken from areas of relatively short grassland on days in July, August and September when the vegetation was sufficiently dry.

Site Grid Reference Site Description

1 TL678771 Calcareous grassland at west end of airfield

2 TL711765 Calcareous grassland at east end of airfield

3 TL695759 Ruderal vegetation and bare ground in waste disposal area

4 TL679774 Coniferous plantation

5 TL677772 Narrow fringe of grassland and scrub along south western

edge of coniferous plantation

6 TL700760 Hawthorn scrub and ruderal vegetation

Table 1. Details of main sites surveyed during 1999


Suffolk Natural History, Vol. 36 96

Results A total of 122 species of spider (including four nationally notable species and one species new to Britain) were identified from RAF Mildenhall during 1998 and 1999.

Table 2. Species recorded from RAF Mildenhall

Amaurobius similis (Blackwall) Dictyna arundinacea (L.) Dictyna uncinata Thorell Dictyna latens (Fabricius) Lathys humilis (Blackwall) Argenna subnigra (O.P.-Cambridge) Dysdera crocata C.L.Koch Harpactea hombergi (Scopoli) Pholcus phalangiodes (Fuesslin) Haplodrassus signifer (C.L.Koch) Zelotes electus (C.L.Koch) Zelotes latreillei (Simon) Trachyzelotes pedestris (C.L.Koch) Drassyllus pusillus (C.L.Koch) Micaria pulicaria (Sundevall) Clubiona reclusa O.P.-Cambridge Clubiona pallidula (Clerck) Clubiona terrestris Westring Clubiona neglecta O.P.-Cambridge Clubiona lutescens Westring Clubiona comta C.L.Koch Clubiona diversa O.P.-Cambridge Cheiracanthium erraticum (Walckenaer) Cheiracanthium virescens (Sundevall) Agroeca inopina O.P.-Cambridge Agroeca cuprea Menge Phrurolithus festivus (C.L.Koch) Xysticus cristatus (Clerck) Xysticus audax (Schrank) Xysticus kochi Thorell Ozyptila praticola (C.L.Koch) Ozyptila sanctuaria (O.P.-Cambridge) Ozyptila atomaria (Panzer) Philodromus dispar Walckenaer Philodromus praedatus O.P.-Cambridge Philodromus cespitum (Walckenaer) Philodromus collinus C.L.Koch Tibellus oblongus (Walckenaer) Salticus scenicus (Clerck) Heliophanus flavipes (Hahn) Euophrys frontalis (Walckenaer)

Pardosa monticola (Clerck) Pardosa palustris (L.) Pardosa pullata (Clerck) Pardosa prativaga (L.Koch) Pardosa lugubris s. l. (Walckenaer) Alopecosa pulverulenta (Clerck) Alopecosa barbipes (Sundevall) Trochosa ruricola (Degeer) Trochosa terricola Thorell Pisaura mirabilis (Clerck) Agelena labyrinthica (Clerck) Tegenaria gigantea Chamberlin & Ivie Tegenaria agrestis (Walckenaer) Hahnia nava (Blackwall) Steatoda bipunctata (L.) Anelosimus vittatus (C.L.Koch) Achaearanea tepidariorum (C.L.Koch) Theridion sisyphium (Clerck) Theridion impressum L.Koch Theridion simile C.L.Koch Theridion melanurum Hahn Theridion bimaculatum (L.) Enoplognatha ovata (Clerck) Enoplognatha latimana Hippa & Oksala Enoplognatha thoracica (Hahn) Robertus lividus (Blackwall) Tetragnatha extensa (L.) (see Cover) Tetragnatha montana Simon Pachygnatha degeeri Sundevall Metellina segmentata (Clerck) Metellina mengei (Blackwall) Zygiella x-notata (Clerck) Gibbaranea gibbosa (Walckenaer) Araneus diadematus Clerck Araneus quadratus Clerck Larinioides cornutus (Clerck) (Plate 13) Nuctenea umbratica (Clerck) Agelenatea redii (Scopoli) Neoscona adianta (Walckenaer) Araniella cucurbitana (Clerck)

Araniella opistographa (Kulczynski)



Site name No. of species recorded Source of data

Minsmere RSPB reserve 241 Wilson, 1999

Center Parcs, Elveden Forest 135 Gibson, 1999

Orford Ness 134 Nellist, 1997

RAF Mildenhall 122 Lee & SMG, 1999

Hollesley Common 121 Cooke, 1963

Hypsosinga albovittata (Westring)

Hypsosinga pygmaea (Sundevall)

Cyclosa conica (Pallas)

Walckenaeria cucullata (C.L.Koch)

Hypomma cornutum (Blackwall)

Pocadicnemis juncea Locket & Millidge

Oedothorax fuscus (Blackwall)

Oedothorax retusus (Westring)

Oedothorax apicatus (Blackwall)

Pelecopsis parallela (Wider)

Pelecopsis nemoralis (Blackwall)

Microctenonyx subitaneus

(O.P.-Cambridge)

Micrargus subaequalis (Westring)

Diplocephalus permixtus

(O.P.-Cambridge)

Diplocephalus latifrons (O.P.-Cambridge)

Araeoncus humilis (Blackwall)

Typhochrestus digitatus (O.P.-Cambridge)

Milleriana inerrans (O.P.-Cambridge)

Erigone dentipalpis (Wider)

Erigone atra Blackwall

Ostearius melanopygius (O.P.-Cambridge)

Meioneta rurestris (C.L.Koch)

Meioneta fuscipalpa (C.L.Koch)

Centromerita bicolor (Blackwall)

Centromerita concinna (Thorell)

Bathyphantes gracilis (Blackwall)

Diplostyla concolor (Wider)

Drapetisca socialis (Sundevall)

Stemonyphantes lineatus (L.)

Lepthyphantes minutus (Blackwall)

Lepthyphantes tenuis (Blackwall)

Lepthyphantes zimmermanni Bertkau

Lepthyphantes cristatus (Menge)

Lepthyphantes mengei Kulczynski

Lepthyphantes flavipes (Blackwall)

Lepthyphantes pallidus (O.P.-Cambridge)

Linyphia triangularis (Clerck)

Linyphia hortensis Sundevall

Linyphia clathrata Sundevall

Microlinyphia pusilla (Sundevall)

This amounts to more than one quarter of the four hundred plus species known from Suffolk. Table 3 shows the handful of sites in the county which are known to support more than one hundred species of spider suggesting that, at least in a local context, RAF Mildenhall is an important arachnological site. However, the number of species recorded from any site is a function of many factors including time spent recording, sampling methods used and diversity of habitats present. Therefore one has to be wary of using species richness alone as an indication of the arachnological value of a site.

Table 3. Suffolk sites with over 100 species of spider recorded

The Breckland fauna The Breckland heaths are known to support a unique spider fauna comprising a mixture of species otherwise associated with calcareous grasslands in southern England, coastal sand dunes and lowland Calluna heaths. Many of the species typical of this fauna were recorded from the two areas of



calcareous grassland at either end of the Mildenhall airfield supporting the view that these areas constitute patches of relict breck grass heath. Two of the nationally notable species, Trachyzelotes pedestris and Agroeca cuprea, are included in this fauna. Trachyzelotes pedestris is one of a group of black, ground living spiders all very similar in general appearance. This nocturnal hunter is an element of the calcareous grassland fauna and is normally found in more open sites with shorter turf and stones. Such sites generally favour hunting species over web builders and other representatives of this short grassland fauna include Argenna subnigra, Pardosa monticola, and a tiny money spider Pelecopsis parallela. Taller calcareous grassland supports more web builders such as Theridion bimaculatum, Hypsosinga pygmaea and Centromerita bicolor but a few hunters also inhabit such sites, e.g. Agroeca inopina.

The nationally notable Agroeca cuprea, is another ground living hunter but this species is usually found in dry coastal habitats. Although it is a typical species of the Breckland fauna it does not occur inland elsewhere. The common and widespread species, Zelotes electus, has a similar distribution pattern.

Merrett (1990) describes the fauna of southern heathland as comprising four groups of species associated with different stages in the succession from burnt ground to mature heather. Although it might be expected that the grass heath fauna would have most affinity with the species groups from the earlier stages of succession on Calluna heathland it is interesting that species from all four of Merrett’s groups were recorded on the RAF Mildenhall grasslands. Early heathland colonists that disappear as the heather regenerates include Xysticus kochi and Typhochrestus digitatus. The wolf spiders Pardosa palustris and Alopecosa barbipes, along with web builders such as Stemonyphantes lineatus and Lepthyphantes tenuis are also early colonisers but are able to survive for longer in the growing heather. Later arrivals include the ground living Drassyllus pusillus and web building Enoplognatha thoracica. These species decline as the heather reaches maturity and are replaced by species such as Dictyna arundinacea, Neoscona adianta and Agelenatea redii. The co-existence at RAF Mildenhall of species from all of these seral stages is probably due to the diversity of structure in the grasslands with a mosaic of bare ground and patches of vegetation of differing heights.

Perhaps the most notable spider found on the site was Meioneta fuscipalpa, a widespread but very local north European species, never before recorded in Britain. A single male specimen of this species was collected in 1998 when it was misidentified as a local British species, Meioneta gulosa, which is thought to be restricted to mountainous areas (Roberts, 1987). Its presence at RAF Mildenhall was believed to be a chance occurrence due to the particular wind conditions at the time. The collection of further specimens of M. fuscipalpa in 1999 from exactly the same area of grassland at the eastern end of the airfield suggests the presence of a breeding population on the site. This area is therefore of great importance as home to the only colony of M. fuscipalpa known to exist in this country.



Site name No. of species SQI Source of data

Cavenham Heath 31 1·6 Duffey, Locket & Millidge, 1957

Ellough 19 1·5

Foxhole Heath 27 2·4 Duffey, Locket & Millidge, 1957

Hollesley Common 121 1·8 Cooke, 1963

Ipswich Airport 45 1·8

Lakenheath Warren 8 1·1

RAF Barnham 21 1·2

RAF Lakenheath 20 2·0 Key et al., 1992

RAF Mildenhall 61 1·9

Comparison with other grasslands For the reasons outlined above, comparisons between the fauna of different sites are fraught with difficulties. Some of the problems can be resolved by ensuring similar habitats are compared and the use of a Species Quality Index (SQI) reduces the effects of variations in recording effort between sites. In Table 4 the importance of the spider fauna of the grass heaths at RAF Mildenhall is compared with other grasslands / grass heaths across Suffolk. Unless otherwise stated the data result from my own fieldwork. SQIs were calculated following Nellist (1994) utilising a standard scoring method of 32 points for Red Data Book, 16 for nationally notable (a), 8 for nationally notable (b), 4 for regionally notable, 2 for local and 1 for common species. The score for all species from a site was then totalled and divided by the number of species recorded to give the SQI.

Table 4. Comparison of Suffolk grassland / grass heath spider faunae

The results suggest that the breck grass heath at RAF Mildenhall is one of the best grasslands in the county with only RAF Lakenheath and Foxhole Heath showing a higher SQI score.

The woodland species A total of 70 species of spider was recorded from a conifer plantation on the air base, more than from any of the other habitats. Although woodland generally supports the greatest diversity of species this is not usually the case with conifer plantations. The high species number is due to the spiders collected from this habitat including not only woodland specialists, e.g. Drapetisca socialis, but also some species associated with breck grass heath e.g. Agroeca cuprea. These latter species were mainly found on the woodland edge where the conifers are separated from the adjacent grass heath by just the width of a public footpath and two security fences. A further nationally notable species, the crab spider Philodromus collinus, was recorded from this habitat. This spider is usually found on the lower branches of trees, especially conifers, in the south east of England. It is often found on pines on mature heathland but in Breckland has found a niche along broad rides and on the edges of conifer plantations.



Species associated with man To varying degrees all areas of RAF Mildenhall have been subject to human interference. Where this influence was greatest, especially around buildings, a number of synanthropic species were collected. Pholcus phalangiodes is a long-legged spider inhabiting undisturbed corners of a range of buildings on the airfield. The comb-footed spiders Theridion melanurum and Achaearanea tepidariorum were also found in a single building in each case. The latter species has only been recorded from West Suffolk once previously and that record dates from the pre-war era. Outdoors the money spider Ostearius melanopygius was collected from locations across the airfield. This species has now become naturalised in Britain but was originally introduced from New Zealand.

Conclusions On the basis of high species richness, the presence of relict semi-natural habitat, a high SQI and the presence of a species new to Britain, RAF Mildenhall is clearly an important county site for spiders. The USAF is to be congratulated on their pro-active approach to identifying areas of nature conservation value and incorporating sympathetic practices into their estate management regimes. There appears to be no immediate threat to the spider fauna of the site and positive management practices are likely to further enhance the diversity.

Acknowledgements I am grateful to Neil Ravenscroft of Suffolk Wildlife Trust Trading Limited for providing the opportunity to be involved in the survey at RAF Mildenhall. Also to Chief Flight Officer Dave Nutt who accompanied me on all visits, providing transport around the site, helping to carry equipment and collect specimens and generally showing a great interest and enthusiasm for the work being undertaken.

References Cooke, J. A. L. (1963). A Preliminary Account of The Spiders of the Flatford

Mill region, East Suffolk. Trans. Suffolk Nat. Soc. 12: 155–176. Duffey, E., Locket, G. H. & Millidge, A. F. (1957). The Spider Fauna of the

Heaths and Fens in West Suffolk. Trans. Suffolk Nat. Soc. 10: 199–209. Gibson, C. W. D. (1999). Elveden Forest Ecological Monitoring Studies 1998.

unpublished report for Center Parcs. Key, R. S., Drake, C. M., Sheppard, D. A. & Proctor, D. A. (1992). An

invertebrate survey of RAF Lakenheath SSSI, Suffolk on 21 June 1992. English Nature Research Report No. 47. English Nature.

Lee, P. and Suffolk Moth Group (1999). The invertebrates of RAF Mildenhall, Suffolk. Unpublished report for SWT Trading Limited.

Merrett, P. (1990). A Review of the Nationally Notable Spiders of Great Britain. Nature Conservancy Council Contract Survey No. 127. NCC

Nellist, D. R. (1994) A survey of the Spiders of Orford Ness, Suffolk, on the 18th and 19th June 1994. Unpublished report of a survey by the British Arachnological Society for the National Trust.

Nellist, D. R. (1997). A Second Survey of the Spiders of Orford Ness, Suffolk. Unpublished report for the British Arachnological Society.



Roberts, M. J. (1987). The Spiders of Great Britain and Ireland Vol. 2 Linyphiidae. Harley Books.

Wilson, R. (1999). Spiders of Minsmere RSPB Reserve, Suffolk. Newsl. Br. arachnol.Soc. 86: 14.

Paul Lee ARACHNE, 155 Corton Road, Lowestoft, Suffolk NR32 4PR

ACULEATE HYMENOPTERA REPORT

Plate 13: Larinoides cornutus (Clerck), an attractively-marked wetland spider

which is often found in long grasses by water. It spins its web on reed heads, with

a silken retreat amongst the florets of the plant (p. 96).

S.

Du

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an

notes on the suffolk list of coleoptera: 7 the genus ischnomera stephens (oedemeridae)

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