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Beetles at Wicken Fen – an introduction
Tony Drane , Coleoptera Recorder – Wicken Fen

Wicken Fen has long been known as a good place for beetles. Since the early days of the 19th century, many notable early coleopterists, including the young Charles Darwin when he was at Cambridge, have collected the Fen's specialities. Although the earliest records are sometimes very imprecise in their localities, there are enough of them to permit comparisons between then and now.

Omer Cooper, Perkins and Tottenham drew attention to certain beetle populations which were showing change during the 1920s and 1930s. Many of the beetles that were declining then have since been found, but there are some notable exceptions. Dromius sigma, a distinctive reed carabid, has yet to be rediscovered, and while it is rash to pronounce a beetle extinct in a particular locality, it is unlikely that it still occurs on the Fen. The large black carabid Pterostichus aterrimus (RDB1 ‘endangered’), once common in the Fens, has not been found for many years. Fortunately, other reed carabids are thriving: Dromius longiceps, Demetrias imperialis, D. monostigma and the bright orange and blue Odacantha melanura.  Another carabid, Panagaeus crux-major (called the Crucifix Ground Beetle) is extremely rare in Britain and classed as RDB1 Endangered. The beetle has a distinctive black cross on predominantly orange-red elytra. According to Wollaston it occurred in ‘immense numbers’ at Wicken in 1842. There were several records between 1900 and 1930 at Wicken, and there are specimens from this period in the Zoology Museum at Cambridge University. After this, there was only one record of a single beetle in 1951 by Mr RC Muir, but no more sightings, so the beetle was thought to be extinct, until it was re-discovered close to the visitor centre in 2008 by Stuart Warrington.

Wicken Fen remains the only site in the fenland of Cambridgeshire and Huntingdonshire for the rare small brown carabid, Trechus rivularis (RDB3 ‘rare’). Clearly the isolation of these fens during the draining and conversion to arable of the surrounding land has threatened the populations of the rarer species and virtually ruled out natural recolonization. Changes at Wicken, such as the taming of Adventurers' Fen during the Second World War, the encroachment of carr on open areas during the extended period of reduced management and the progressive drying of the Fen have undoubtedly led to some casualties among the beetle fauna. Some of the old species from the Fens have become nationally rare: Pterostichus aterrimus (RDBI), Chlaeius tristis (RDB2 'vulnerable'), Spercheus emarginatus (RDB1, probably extinct in Britain), Hydraena palustris (RDB2), Oberea oculata (RDBI) and Lixus paraplecticus (RDB1). It should not be surprising that they are now rare or extinct on the Fen. O. oculata, common to the collectors of old but not seen for many years, had been given up for lost when it suddenly turned up in 1984 before a non-coleopterist who photographed a specimen on sallow. There may well be a reasonable population of this attractive red and black longhorn; it is a renowned recluse, hiding under leaves or flying over the sallow and alder buckthorn. Renewed efforts are to be made to establish its status at Wicken. Lixus paraplectius, an inch-long narrow weevil, sometimes with a golden bloom in new specimens, was a Wicken speciality, and it appears on Omer Cooper and Tottenham's list of 1932. It has not been seen for many years, perhaps because one of its food plants, greater water-parsnip (Sium latifolium), has disappeared from the Fen. 

Despite these fluctuations and declines the Fen still has a wonderfully rich beetle fauna. Few sights are more dramatic than the two-inch long iridescent greeny bronze cerambycid Aromia moschata, the musk beetle, flying slowly over the sallows on a hot August day, and coming down to rest on a flower. Often seen basking in the sun on flowerheads and low vegetation are the yellow and black longhorn, Strangalia maculata, the golden-bloomed grey longhorn Agapanthia villosoviridescens and the ashy grey longhorn Anaglyptus mysticus with chestnut shoulders to its elytra.

The reeds and sedges lining the lodes and dykes often have a number of the chrysomelid reed beetles (Donacia spp.) clinging to their leaves. Sometimes the dwarf willows and low vegetation can be infested with the large golden green chrysomelid Chrysolina graminis, while on the sallows occur two characteristic fen- land weevils with silvery gold scaling, Acalyptus carpini and Dorytomus salicinus. With so much water, it is perhaps not surprising that Wicken Fen supports a very rich water beetle fauna. Among the more uncommon species are Agabus undulatus (RDB2), with its characteristic orange zigzag markings across the base of the elytra, which can be met with in the Brickpits, and A. uliginosus, which occurs in the more boggy areas. All five of the spectacularly large lowland dytiscids have been found: Dytiscus circumcintus, D. circumflexus, D. dimidiatus (RDB3), D. marginalis and D. semisulcatus. While these species occur in more open ditches, the very old, overgrown ditches on the Fen are valuable habitat for beetles, including such fenland specialists as Dryops anglicanus and the hydrophilid Hydraena palustris (RDB2).

The great majority of the Fen's beetles are small and dull in colour and can be found only by sieving the reed and sedge leaf- litter or by sweeping the vegetation. With a list of over a thousand different species of beetle, Wicken Fen is a most valuable site for Coleoptera. The sustained management effort of recent years should maintain the Fen's diversity of habitats, thus ensuring the survival of its special beetle populations.

This article is from Wicken Fen – the making of a wetland nature reserve edited by Laurie Friday and published by Harley Books.

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