Rediscovery of the woodland grasshopper Omocestus rufipes in East Suffolk

EFFECTS OF FOREST MANAGEMENT ON ACULEATES

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Rediscovery of the woodland grasshopper Omocestus rufipes in East Suffolk The Nationally Scarce woodland grasshopper Omocestus rufipes (Orthoptera: Acrididae, Plate 12) is a rare insect north of the Thames Estuary in the UK (Marshall & Haes 1988). Typical habitats in England are woodland rides/ clearings and grassland or heath near to woodland edge. In East Anglia, the only recent records are from East Suffolk, predominantly in the Dunwich area.

There was one observation from Essex in 1974, but this population is thought to be extinct due to woodland encroachment onto the open heathland (Gardiner & Gardiner 2010). The East Suffolk records were collected by Mike Edwards in August 1996. Mike's observations were from Blaxhall Common, Dunwich Heath (National Trust), Hinton Pit, New Delight Walks, Tunstall Common, and Walberswick Common, in three 10 Ă— 10 kilometre squares (TM35, 46, 47).

The woodland grasshopper has not been recorded in East Suffolk since Mike's observations, so the author decided to visit several of the old sites in warm weather on 2–3 September 2011. The grasshopper was not found at several sites including Dunwich Heath (NT), New Delight Walks, Toby's Walks, and Walberswick Common. However, on 3 September, a mating pair (at TM454696) was discovered during an extensive search at Westleton Heath (Natural England managed site). The pair was captured in a jar for inspection of the distinctive white palps. A singing male was heard to provide a further confirmation of the observation. The habitat was acid grassland and heather Calluna vulgaris, interspersed with numerous mature birch Betula pendula trees. Patches of purple moor-grass Molinia caerulea fringed the occupied habitat indicating wetter heathland.

After the success at Westleton Heath, the author visited Dunwich Forest to find the coniferous woodland extensively grazed by Dartmoor ponies. The Forestry Commission manages the Forest and their intention is to create grazed open woodland as trees are felled. However, the grazing appeared to be detrimental to the herbaceous understorey leaving little suitable habitat for the woodland grasshopper, which requires diversity in grassland structure (e.g. tall and short vegetation). Moving on from the plantation, the author stopped to inspect ungrazed open heathland on the edge of Dunwich Forest (TM454722), where a female woodland grasshopper was recorded, and captured in a jar for definitive identification of the white palps. A singing male was also heard to confirm the identification. Once again the habitat was open heathland interspersed with birch trees.

Dartmoor ponies were grazing on the north side of the road adjacent to Dunwich Forest. Unfortunately, they did not leave much taller vegetation (apart from bracken Pteridium aquilinum) that would be suitable for the woodland grasshopper (see Plate 10), which was absent from this closely cropped sward. Concerns have been raised about the negative effect of pony overgrazing upon the orthopteran assemblages of the New Forest (Tubbs, 1986; Pinchen, 2000; Denton, 2006) and Mardyke River Valley (Gardiner & Haines, 2008). Denton (2006) outlines the importance of exclosures, from

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which grazing ponies are largely excluded, for Orthoptera in the New Forest.

For example, both the woodland grasshopper and the wood cricket Nemobius sylvestris were found in exclosures; the varied and taller vegetation structure created in the absence of excessive grazing being particularly important (Denton, 2006). In the Mardyke Valley, only four species were recorded in pony grazed floodplain, compared to seven in ungrazed pastures (Gardiner & Haines, 2008). Therefore, introduction of pony grazing to any heathland in the Dunwich Forest area with a significant orthopteran assemblage should be avoided. In Dartmoor pony grazed woodland and heathland at Dunwich Forest only two species were observed by the author (field Chorthippus brunneus and mottled Myrmeleotettix maculatus grasshoppers). However, in ungrazed heathland with scattered birch trees, six species were observed including the mottled, woodland, and stripe-winged Stenobothrus lineatus grasshoppers.

References Denton, J. (2006). Assessment of potential effects of different grazing regimes in Wootton Coppice and Holmsley inclosures. Unpublished report.

Gardiner, T. & Gardiner, M. (2009). Scrub encroachment leads to the disappearance of the Common Green Grasshopper Omocestus viridulus (Orth.: Acrididae) from heathland at Mill Green Common in Writtle Forest. Entomologist’s Record & Journal of Variation 120: 63–67.

Gardiner, T. & Haines, K. (2008). Intensive grazing by horses detrimentally affects orthopteran assemblages in floodplain grassland along the Mardyke River Valley, Essex, England. Conservation Evidence 5: 38–44.

Marshall, J. A. & Haes, E. C. M. (1988). Grasshoppers and Allied Insects of Great Britain and Ireland. Harley Books, Colchester.

Pinchen, B. J. (2000). Evaluation of five inclosures in the New Forest for invertebrate conservation and potential impact of grazing. Unpublished report.

Tubbs, C. R. (1986). The New Forest. Collins, London.

Tim Gardiner tim.gardiner@environment-agency.gov.uk

Trans. Suffolk Nat. Soc. 47 (2012)

T. Gardiner A. Wood

Plate 10: Dartmoor ponies grazing on the north side of the road adjacent to Dunwich Forest (p. 53).

Plate 12: The Nationally Scarce woodland grasshopper Omocestus rufipes (p. 53).