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Trans. Suffolk Nat. Soc. 48 (2012)

THE DISCOVERY OF LESNE’S EARWIG IN HOLBROOK BAY INCLUDING AN ASSESSMENT OF THE IMPORTANCE OF THE SHOTLEY PENINSULA FOR

DERMAPTERA AND ORTHOPTERA TIM GARDINER

Introduction Lesne’s Earwig Forficula lesnei (Dermaptera: Forficulidae) is a Nationally Scarce insect in the UK. There are very few recent records from Suffolk (Hawes 1997; Sanford 1997) and it is hard to ascertain its distribution due to it probably being under-recorded in the county. The earwig is easily identified by the straightened cerci up to half its length in the male (Fig. 1); it is also smaller and generally paler in colour than the Common Earwig Forficula auricularia and has much reduced or absent wings (Marshall & Haes, 1988). Recently (12 August 2012), I recorded Lesne’s Earwig at Hogmarsh Nature Reserve (opposite Manningtree and just over the Suffolk border) on a railway embankment, where two males were beaten from Oak Quercus robur (TM102326), and also from the Essex side of the River Stour on Ash Fraxinus excelsior and Oak fringing sea wall flood defences which stretch from Manningtree to Cattawade Marshes. These observations were new 10 × 10 km square records (TM03 and TM13) and suggested that the earwig could be found at other sites along the Stour Estuary. With these sightings in mind, I decided to visit Holbrook Bay on the Shotley Peninsula in September 2012 to see if I could find Lesne’s Earwig in coastal scrub and trees in a beating survey. This short paper presents the results of this beating survey and discusses the importance of the Shotley Peninsula for Dermaptera and Orthoptera (grasshoppers and crickets).

The survey Parking at Lower Holbrook on 3 September 2012, I walked down the track leading to the sea wall beating trees as I went, but no Lesne’s Earwigs were found. Walking westward along the sea wall flood defence which protects low-lying grazing pasture before the land rises to the Royal Hospital School, I started beating scrub and trees along the folding (flat area of land between the landward toe of a sea wall embankment and the borrowdyke) and quickly found the first Lesne’s Earwigs near Holbrook Boat House (at TM173348) where two males were beaten from Bramble Rubus fruticosus agg. Continuing along the folding, a further male was beaten from an isolated patch of Bramble by the borrowdyke (at TM172346) near Holbrook School Sluice. From here on as I progressively beat my way toward Markwell’s Farm, no more Lesne’s Earwigs were found as the patches of scrub became very infrequent and the sea wall was predominantly tussocky grassland with scattered Oak trees.

Once I had reached the western extent of the public footpath near Markwell’s Farm, I returned to Holbrook Boat House beating Bramble scrub fringing the public footpath on the sea wall crest. No Lesne’s Earwigs were beaten until I reached a patch of Bramble scrub near Holbrook School Sluice (Plate 7) on the seaward side of the crest. Two males were beaten from this scrub (at TM172346), despite it being cut over winter 2010/2011 by the

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Environment Agency (EA), the regenerating Bramble displaying quite vigorous regrowth since mowing. The seaward slope is to be cut by the EA on a four year rotation (i.e. one cut every four years) to allow inspection of the integrity of the flood defence by engineers, this should enable Lesne’s Earwig to survive on the embankment. During the cut, scrub and trees along the borrowdyke will remain uncut as a refuge for species such as Lesne’s Earwig.

Returning to the track which leads to Lower Holbrook as the evening progressed; I decided to walk eastward toward Harkstead Beach causing some annoyance to a local wildfowler as I disturbed some geese while furiously whacking bushes. A light aircraft buzzed over the Bay against the backdrop of the setting sun, providing a temporary respite to the searching and some wonderful views for a weary earwig hunter.

A small sea wall flood defence protects farmland which rises gently upwards above the Bay in the Alton Wharf area, and has three stunted Oak trees on the crest. From these trees over 30 Common Earwigs were beaten, but no Lesne’s Earwigs were observed. Travelling eastward, scrub and trees on the sandy cliffs approaching Harkstead Beach (area shown as The Grove on Ordnance Survey maps) were furiously beaten, but no Lesne’s Earwigs were observed despite plentiful Common Earwigs. As it was getting dark, I decided to call off the search and returned to the car.

On the evening of 5 September I returned to continue the beating from where I had left off and commenced beating trees from The Grove near to Harkstead Beach toward the eastern extent of the Bay where the cliffs rise again. Here Hawthorn Crataegus monogyna scrub was beaten and Lesne’s Earwig males were taken from TM186339 (one male) and TM187338 (two males). The scrub was growing out of the sandy cliffs favoured by geologists and was restricted to a 100 m section. Therefore, it appears that Lesne’s Earwig is restricted to sporadic Hawthorn scrub on the cliffs to the east of the Bay at Harkstead. Haes & Harding (1997) have sea cliffs listed as a habitat for Lesne’s Earwig; perhaps the microclimate is suitable for the insect in these locations, particularly as the Harkstead cliffs are south-west facing and receive plenty of solar radiation.

The final session of beating was on 9 September in hot sunshine and focused on the western extent of Holbrook Bay at Stutton Ness. Parking at Stutton village, I walked down the public footpath to Stutton Ness passing Crepping Hall and Backhouse Ley. Occasional stops were made to beat trees on the way to the Ness, but no Lesne’s Earwigs were found. Arriving at Graham’s Wharf, I targeted scrub along the borrowdyke of a short section of sea wall, but could not locate Lesne’s Earwig. The sea wall had recently been mown but plenty of scrub remained uncut along the borrowdyke edge, so the apparent absence of the earwig was probably not related to EA management of the flood defence. From Graham’s Wharf to Stutton Ness, numerous trees were beaten along the sandy cliffs, including Hawthorn and Oak, but also Butcher’s Broom Ruscus aculeatus which was indicative of the acidic soil. A brief cessation in the beating allowed enjoyment of the magnificent views of Holbrook Bay from the Ness.

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I couldn’t resist taking a look in what seemed to be an old gravel pit on top of the cliffs which was fringed almost entirely by Bramble. However, no Lesne’s Earwigs were located (although Common Earwigs were plentiful) despite the interesting flora of the acidic soil. The gravelly floor of the pit was heavily grazed by rabbits which appear to have maintained the very short sward free of scrub encroachment with large patches of moss and exposed ground frequented by numerous Field Grasshopppers Chorthippus brunneus. On the edge of the pit and the cliffs, other plants of heathy ground such as Broom Cytisus scoparius, Butcher’s Broom, Common Cudweed Filago vulgaris and Wood Sage Teucrium scorodonia were noted. Sadly, much of this interesting habitat has been lost due to the planting of various tree species (including non-native pines) on the surrounding land restricting the heathy flora to the pit and cliffs where unmanaged scrub encroachment is clearly a serious issue.

As the day was still young, I walked along the shore periodically beating trees, westward from Stutton Ness to Stutton Mill just as the coast opens out into Seafield Bay. Once again, no Lesne’s Earwigs were beaten, despite apparently suitable Hawthorn scrub on the sandy cliffs. At Stutton Mill I walked inland toward Stutton village along a public footpath which ran down a track. Again despite furious beating, no earwigs of the target species were obtained. Having now covered a large portion of Holbrook Bay and coast up to Stutton Mill to the west, the distribution of the earwig in the area was now apparent.

Overview of the distribution in Holbrook Bay Lesne’s Earwig has a localised distribution in Holbrook Bay, being found on scrub fringing the borrowdyke and on the crest of the sea wall from Holbrook Boat House to Holbrook School Sluice, but absent from the rest of the flood defence toward Markwell’s Farm probably due to the lack of significant patches of scrub. Lesne’s Earwig was also found on a short stretch of scrub on the sandy cliffs near Harkstead. A total of eight males were recorded from five locations in the Bay, with the insect being comfortably outnumbered by the Common Earwig. It is possible that the absence of wings makes dispersal difficult for Lesne’s Earwig, which may explain why it appears localised to specific patches of scrub in Holbrook Bay. Lesne’s Earwig also seems to be entirely restricted to the sea wall and cliffs; none were beaten inland in the Lower Holbrook and Stutton village area.

Interestingly, Lesne’s Earwig was only beaten from Bramble and Hawthorn scrub in Holbrook Bay and not trees such as Ash and Oak along the sea wall from which it has been recorded on flood defences in the Cattawade Marshes and Manningtree area of the Stour Estuary. This suggests that the earwig may have preferences for differing scrub and tree species depending on the location. In Holbrook Bay, Lesne’s Earwig was largely absent from alluvial soil, which supported populations on Ash and Oak at Cattawade Marshes and Manningtree. Well-drained (acidic), sandy and silty soils were the main substrate for the Bramble and Hawthorn scrub which Lesne’s Earwig inhabited in the Bay, suggesting that the insect is not necessarily found on

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base-rich soils as the literature suggests (Marshall & Haes, 1988; Haes & Harding, 1997). Due to the questions arising from this study, further research is needed to understand its habitat preferences in the UK.

It should be borne in mind that this was a small-scale study of eight hour’s searching, spread across three days in September 2012. The lack of public access to the west of the Bay between Markwell’s Farm and Graham’s Wharf means no beating was conducted here. Therefore, it is possible that populations of the earwig remain to be discovered in the Bay.

The importance of the Shotley Peninsula for Dermaptera and Orthoptera The discovery of Lesne’s Earwig in Holbrook Bay, but also at Hogmarsh near Manningtree, provides the first records of this Nationally Scarce insect on the Shotley Peninsula. Beating at other locations on the Peninsula, notably the woodlands surrounding Pin Mill, provided no more sightings of the earwig, suggesting that it is not necessarily widespread in the area despite its presence in the Bay. The earwig is currently the highlight of the orthopteroid fauna of the northern side of the Stour Estuary on the Shotley Peninsula (from Cattawade to Shotley Gate), which appears to be relatively species-poor (only two and eight species of Dermaptera and Orthoptera recorded respectively). Contrastingly, the Essex (south) side of the Estuary (from Manningtree to Harwich) has a higher number of species recorded (two and 11 species of Dermaptera and Orthoptera respectively).

To put the species richness along the Stour Estuary into context, 18 orthopteroid species (Dermaptera, Dictyoptera (cockroaches) and Orthoptera) have been recorded on the Essex coast making it a particularly favourable area for these insects nationally (Gardiner 2012). Therefore, 72% (13 species) of the Essex species-pool has been recorded on the southern side of the Stour Estuary, contrasting with 56% (10 species) for the northern coast on the Shotley Peninsula. It is probable that many of the coastal orthopteroids are at the limit of their range in the UK due to climatic factors (Marshall & Haes, 1988), so the lower number of species to the north of the Stour Estuary is perhaps not that surprising.

The three orthopterans recorded on the Essex side of the Stour Estuary, but not yet on the Shotley Peninsula, are the two groundhoppers (Tetrix subulata and undulata) and the Great Green Bush-cricket Tettigonia viridisimma, an Essex Red Data List species. This might seem a little puzzling as the northern (Shotley Peninsula) side of the Estuary has south facing cliffs and sea walls which should have an ideal warm microclimate suitable for Dermaptera and Orthoptera. However, the Shotley Peninsula lacks the large (coppiced) ancient woodlands, in which the Common Groundhopper is found (in the RSPB’s Stour Wood which is 54 ha in size), of the southern shore in Essex. It also lacks the extensive wildlife reserves such as Wrabness Nature Reserve (22 ha in size), from which the Great Green Bush-cricket has been recorded in Essex. Therefore, the absence of species may relate to a genuine dearth of favourable orthopteroid habitats. Despite the apparent lack of good habitats, further surveys are needed on the Peninsula to confirm whether other species are present as the area is currently under-recorded for Dermaptera and Orthoptera.

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References Gardiner, T. (2012). How does mowing of grassland on sea wall flood

defences affect insect assemblages in eastern England? In: Zhang W-J. (Ed.) Grasslands: Types, Biodiversity and Impacts, Nova Science Publishers, Inc., New York. pp. xi–xxix.

Haes, E. C. M. & Harding, P. T. (1997). Atlas of Grasshoppers, Crickets and Allied Insects in Britain and Ireland. The Stationery Office, London.

Hawes, C. (1997). Earwigs on camera. White Admiral 38: 8–9. Marshall, J. A. & Haes, E. C. M. (1988). Grasshoppers and Allied Insects of

Great Britain and Ireland. Harley Books, Colchester. Sanford, M. (1997). Earwigging. White Admiral 38: 5–8.

Tim Gardiner Environment Agency Iceni House Cobham Road Ipswich Suffolk IP3 9JD

Footnote In early October 2012, Eric Patrick found several males of Forficula lesnei at Landguard Common, TM2831. Tim Gardiner was able to confirm the identification from photos sent via SBRC (see below). This extends the distribution to the eastern end of the Stour/Orwell estuaries and suggests further survey in Suffolk would be worthwhile, particularly on the peninsula between Harkstead and Shotley and also further north on both banks of the Orwell. Ed.

Figure 1. Specimen of Forficula lesnei collected by Eric Patrick at Landguard Common. Note long straight section at base of cerci and lack of wings. (Photo: B. Heather)

Plate 7: Holbrook creek, seawall habitat for Lesne’s Earwig (p. 83).

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