THE STAG BEETLE, LUCANUS CERVUS L. A HYPOTHESIS FOR ITS DISTRIBUTION IN SUFFOLK

STAG BEETLES IN SUFFOLK

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THE STAG BEETLE, LUCANUS CERVUS L. (COLEOPTERA: LUCANIDAE): A HYPOTHESIS FOR ITS DISTRIBUTION IN SUFFOLK COLIN J. HAWES Distribution Britain’s largest terrestrial beetle, Lucanus cervus is mostly restricted to the warmer, drier south-east of England, the principal regions for the insect being London and the Thames Valley, north Essex/south Suffolk, north Kent and areas along the south coast (Napier, 1999).

In Suffolk the beetle is largely confined to the south-east of the county in an area between the rivers Deben and Stour (Map 1). There are significant colonies in Woodbridge, Ipswich, Hadleigh and Nayland, along an imaginary line in the north of this region, and at a number of sites across the Felixstowe and Shotley peninsulas (Hawes, 1998; 1999).

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Map 1. Stag beetle (Lucanus cervus L.) distribution in Suffolk with loamy soils and rivers. (Source : Suffolk Biological Records Centre)

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Factors determining distribution The requirements of a species at every stage of its life-cycle will ultimately determine its distribution. Habitat availability, climate, edaphic factors and competition may all play a part.

Factors affecting the distribution of the stag beetle are likely to be numerous. Dead-wood habitat availability is known to be essential. The beetle relies on dead, decaying broadleaved wood for egg-laying and larval development (Hawes, 1998; Tullett, 1998). Other possible factors limiting its distribution include temperature and soil type, and it is these in particular that are considered in more detail in this paper.

Temperature Analysis of the 1998 National Stag Beetle Survey data carried out by the People’s Trust for Endangered Species (PTES) indicates a good correlation between the current distribution of the insect and areas of highest mean temperature (measured as Accumulated Day Degrees (ADD) : Plate 8). The highest ADD temperatures for Suffolk occur in the south and east of the county.

Larvae and pre-emergence imagos are usually found some 30-50 cm below the soil surface (pers. obs.; Tochtermann, 1987) where they are afforded protection from extremes of temperature. However, there will be a minimum temperature below which imagos are unable to become very active. Air temperature may therefore be acting as the cue for emergence above ground.

Fig. 1 shows that during April and May the air temperature and the number of stag beetles increase simultaneously (Bassford, Keeble & Percy, 1999). Cold or wet weather has been noted to set back emergence (Hawes, 1998).

Fig. 1. Air temperature (Source: Meteorological Office website) and number of stag beetles reported per month during the 1998 National Stag Beetle Survey (Source : PTES).

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Soil Soil plays an important role in the life of the beetle.

• Eggs are usually laid 30-50cm below ground level (Tochtermann, 1992), the female burrowing down through the soil to reach a suitable egg-laying site adjacent to, or in decaying wood.

• Larvae move into the soil to pupate, where they use soil particles to build a cocoon (Horion, 1958; Palm, 1950 : In Klausnitzer 1995).

• Imagos overwinter in their cocoons, up to 45cm below the soil surface (pers. obs.).

• Imagos emerge from the soil by digging an almost vertical tunnel to the surface (Klausnitzer 1995).

It seems reasonable, therefore, to suggest that burrowing, cocoon building, overwintering and emergence above ground could all be affected by soil type, the physical properties of different soils enhancing or limiting the beetles’ ability to inhabit particular areas.

Sensing a pattern to the beetle’s occurrence in Suffolk, its distribution data was overlaid on maps of the surface geology, soils and rivers of the county to see if there was any correlation..

Suffolk comprises several distinct regions and landscapes which are largely the product of different soils. These soils are mostly derived from glacial drift which masks the solid geology (Martin : In Dymond and Martin, 1999), chalk forming the dominant underlying rock in western and central Suffolk, and crag in the east. Heavy boulder clay covers most of central Suffolk giving way on either side to large areas of lighter, sandy soils. To the west these overlie the chalk, while in the extreme north-west they dip beneath the peats of the Fen basin. In the east a large complex of well-drained sand and gravel soils covers the crags, except to the south on the Shotley and Felixstowe peninsulas, where the covering is a wind-blown loess known as cover-loam (Martin : In Dymond & Martin, 1999).

Map 1 shows that stag beetles in Suffolk occur predominantly on the deep, well-drained, loamy soils overlying sands and gravels on the Shotley and Felixstowe peninsulas, and on the loamy soils of river valleys (Sheet 4, 1983).

Areas of clay and chalk seem to be avoided (Hawes, 1999; Napier 1999) .

Heavy soils are likely to be unsuitable for stag beetles, becoming either too sticky and waterlogged or too dried and hard, conditions which would restrict burrowing and emergence. Such conditions are also likely to affect the mobility of the larvae when moving from their feeding substrate (decaying wood) into the soil in order to pupate. Additionally, heavier soils may not provide sufficient aeration for respiration during the larval, pupal and overwintering stages.

Thin soils covering chalk would not provide the depth that seems to be required by the beetle, whilst sandy, heathland soils are perhaps too light and dry to provide the moisture requirements of the insect. Stag beetle larvae are noted to have a higher moisture requirement than their closest British relatives (Klausnitzer ,1995).

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Deep, loamy, well-drained ground seems to provide the best conditions for these insects. Here they encounter no difficulty in burrowing or digging their way to the surface, and the soil is likely to be well-aerated and contain sufficient moisture for the beetles’ development.

Summary The geographical distribution of the stag beetle is likely to be determined by a combination of factors which include, for example, the availability of deadwood habitat, the insect’s dispersal capacity, competition, air temperature, surface geology and soil type.

The availability of dead, broadleaved wood is known to be essential, but the choice of egg-laying site may also be influenced by such factors as the timber’s degree of decay, its moisture content and the presence of specific fungi (Bowdrey, 1997).

Dispersal capacity is obviously dependent on female beetles. Females are reported to stay close to the site from which they emerge, walking in search of suitable, adjacent dead-wood egg-laying habitat, rather than flying (Tullett, 1998). Dispersal would therefore be limited, especially where a colony is centred on a small isolated area, or in a single tree stump situated in a park or garden.

Little is known about competition between the stag beetle and other species. However, it has been observed that larvae of all three British species of Lucanidae (Lucanus cervus, Dorcus parallelipipedus and Sinodendron cylindricum) can inhabit the same piece of decaying wood (Owen, 1992).

Whitehead (1993) notes that the stag beetle is recognised as a thermophilous species in Britain and Eurasia. Temperature appears to play a major role in restricting the stag beetle’s distribution. Data collected and analysed by the PTES point to a strong correlation between areas of the UK with the highest ADD temperatures and the pattern of distribution shown by the beetle.

Hawes (1998) suggests a link between stag beetle distribution and soil type in Suffolk. The pattern of occurrence revealed by the National Stag Beetle Survey (1998) seems to support such a relationship (Napier, 1999; Bassford, Keeble & Percy, 1999). Stag beetles spend most of their life in the soil. The physical properties of different soils might therefore enhance or inhibit the insect’s ability to inhabit particular areas. Detailed analysis of the data collected for Suffolk (Hawes, 1998; 1999) shows that stag beetle strongholds occur predominantly on deep, well-drained, loamy soils overlying sands and gravels, and on the loamy soils of river valleys.

The solid/surface geology of a region will largely determine its soil types.

Whitehead (1993), Hawes (1999) and Napier (1999) draw attention to a possible close correlation between underlying geology and the pattern of stag beetle occurrence. Further examination of maps which show the solid and surface geology for Suffolk (e.g. Chatwin (1961); South Sheet (1979) and Wymer: In Dymond & Martin, 1999) appears to confirm this relationship.

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Conservation Relevant and useful conservation measures can only be applied once the requirements of the stag beetle are understood. If air temperature and soil type combine to limit the insect’s distribution, it should be possible to predict where this Biodiversity Action Plan species could survive and ensure that these areas contain a continuity of suitable dead-wood habitat.

Action Plans The stag beetle Lucanus cervus L. is classified as ‘Nationally Scarce Category B’ in the U.K., which means that it is likely to occur in 100 or fewer 10-km squares of the national grid.

In 1995, the UK Biodiversity Steering Group wrote a Species Action Plan (SAP) for the stag beetle. In 1998, the People’s Trust for Endangered Species became the Lead Partner in implementing the SAP, with English Nature as the Contact Point. A Suffolk Biodiversity Action Plan for the stag beetle was published in June 1998 (Suffolk Biodiversity Working Group, 1998). The County Lead Partner is Colin Hawes.

Acknowledgements The author gratefully acknowledges the help given by the People’s Trust for Endangered Species, especially Dr. Valerie Keeble. I am indebted to her and to the other members of the Stag Beetle Focus Group for generously giving permission to reproduce material from the draft version of the Stag Beetle Report 1999 : Findings of the 1998 National Stag Beetle Survey.

I also thank Andrew Tullett for permission to use data from his unpublished M.Sc. dissertation : Conservation Status and Habitat Requirements of the Stag Beetle Lucanus cervus (L.), in Britain. Thanks are also due to Martin Sanford of the Suffolk Biological Records Centre for providing the Suffolk distribution map. This was produced using DMAPW software written by Dr. Alan Morton (Dept. of Pure and Applied Biology, Imperial College, Silwood Park, Ascot, Berks, SL5 7PY).

References Anon. (1995). Biodiversity : The UK Steering Group Report. HMSO, London.

Bassford, G., Keeble, V. & Percy, C. (1999). Stag Beetle Report : Findings of the 1998 National Stag Beetle Survey (draft). People’s Trust for Endangered Species, London.

Bowdrey, J. (1997). The Stag Beetle Lucanus cervus L. (Coleoptera: Lucanidae) in north-east Essex : Results of the 1996 Colchester ‘Search for Stag Beetles’survey, The Essex Naturalist, 1997: 79-88.

Chatwin, C. P. (1961). British Regional Geology : East Anglia and Adjoining Areas. HMSO, London.

Hawes, C. J. (1998). The Stag Beetle Lucanus cervus L. (Coleoptera: Lucanidae) in Suffolk – a first report. Trans. Suffolk Nat. Soc., 34: 35-49.

Hawes, C. J. (1999).The Stag Beetle Lucanus cervus L. (Coleoptera: Lucanidae) – The 1998 National Survey – An interim report. Trans.

Suffolk Nat. Soc., 35: 71-75.

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Klausnitzer, B. (1995). Die Hirschkäfer. Westharp Wissenschaften, Heidelburg.

Martin, E. (1999). In : Dymond, D. & Martin, E. (eds). An Historical Atlas of Suffolk. Suffolk County Council, Ipswich.

Napier, D. (1999). The 1998 National Stag Beetle Survey. Antenna 23(2): 7781. Bulletin of the Royal Entomological Society.

Owen, J. A. (1992). Lucanids in the garden. Entomologist’s Record and Journal of Variation. 104: 326.

Sheet 4. (1983). Eastern England. Soils of England and Wales. Ordnance Survey, Southampton.

South Sheet. (1979). British Geological Survey (3rd Edition).

Suffolk Biodiversity Working Group (1998). Suffolk Local Biodiversity Action Plan. Suffolk County Council, Ipswich.

Tochtermann, E. (1987). In : Klausnitzer, B. (1995). Die Hirschkäfer. Westarp Wissenschaften, Heidelburg.

Tochtermann, E. (1992). Neue biologische Fakten und Problematik der Hirschkäferförderung. Allg. Forst Zeitschrift. 6/1992: 308-311.

Tullett, A. G. (1998). Conservation status and habitat requirements of the stag beetle, Lucanus cervus (L.), in Britain. A dissertation submitted to the University of East Anglia for the degree of Master of Science in Applied Ecology and Conservation.

Whitehead, P. F. (1993). Lucanus cervus (L.) (Coleoptera : Lucanidae) in Worcestershire with a hypothesis for its distribution. Entomologist’s Mon. Mag. 129: 206.

Wymer, J. (1999). In : Dymond, D. & Martin, E. (eds). An Historical Atlas of Suffolk. Suffolk County Council, Ipswich.

Colin Hawes 3 Silver Leys Bentley Ipswich IP9 2BS

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Plate 8: Map showing accumulated day degrees (ADD) from April to September in the South East of England and the sightings collected during the 1998 National Stag Beetle Survey (p. 66). (Source: FRCA)