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The Fauna Of Tunbridge Wells And Rusthall Commons - Part 8

Robber flies are a group of fierce predators which capture smaller insects with their spiny fore-legs. A number, like the widespread Machimus atricapillus, are characteristic of open areas where they perch on bare sand, rocks or low vegetation, waiting for suitable victims. Other forms, such as the shiny black Laphria marginata and Neoitamus cyanurus with its metallic blue tail, are found in woodland areas and may be spotted on sunlit foliage beside footpaths. Much smaller predators are the long-headed flies, often metallic green or silvery in colour, many of which are also to be seen on sunlit foliage or around the edges of ponds. The males of the most conspicuous, Poecilobothrus nobilitatus, have white-tipped wings which are waved in its courtship display as large numbers of both sexes swarm over damp mud. Soldier flies are brightly coloured sun-loving insects, of which those found on the Commons include the metallic green Chloromyia formosa and the three-coloured Sargus bipunctatus. The bee-fly Bombylius major, as its name suggests, resembles a brown bumblebee, and is frequently seen in spring exploring the nest sites of solitary bees, in which its larvae live as parasites, or hovering in front of flowers and probing them with its long rigid proboscis.

The largest member of the Diptera found on the Commons is the impressive marbled-winged cranefly Tipula maxima. Craneflies, with their enormously long legs, are an easily recognized group of insects, and the familiar medium-sized forms, some patterned with yellow and black, are widespread in the grassy areas of the Commons, as is the shiny black St Mark’s Fly ( Bibio marci), named after its characteristic swarming flight in spring. The flies of the family Tachinidae spend their larval stage as internal parasites of other insects, usually caterpillars, but the bristly adults often feed conspicuously at flowers, and some are brightly coloured. One of the most numerous species on the Commons is the red-spotted Eriothrix rufomaculatus which can be found visiting ragwort. The beautifully metallic greenbottles ( Lucilia spp.) are among the most abundant of many Diptera species which rest in open view on sunlit foliage and tree trunks; others include the shiny black Mesembrina meridiana with its bright yellow wing bases. Numerous species of beetles occur on the Commons. Although the majority are inconspicuous creatures, there are some which by reason of their size or colour may bring themselves to the attention of the non-specialist. The majority of the fast-moving predatory ground beetles are nocturnal, but a number of metallic brassy species make themselves conspicuous by running across sunlit paths. The related Green Tiger Beetle ( Cicindela campestris), a brightly coloured species which flies readily in hot weather, is sometimes seen in similar situations. The ladybirds, whose bright colours advertise them as distasteful to birds, are also predators, feeding on aphids. Such species as the very common Seven-spot ( Coccinella septempunctata) and smaller Two-spot ( Adalia bipunctata) Ladybird hibernate as adults and me in evidence on sunny days in winter. Aquatic predators include the impressive Great Diving Beetle ( Dytiscus marginalis), found with many related forms in the various ponds on both Commons.

Many beetles feed on plant foliage, keeping themselves well hidden, but some of the Chrysomelidae or leaf beetles are brightly coloured, as are the metallic green leaf weevils ( Phyllobius spp.) found on various trees and low-growing plants. The Variable Reed Beetle ( Plateumaris sericea), found on emergent vegetation at the fringes of ponds, may be bronze, copper, deep blue or purple in colour. Of the beetles which feed actively at flowers, the most abundant is the soldier beetle Rhagonycha fulva, orange with black tips, a characteristic insect of high summer. Several related species occur in smaller numbers, all being particularly fond of the tall flower heads of umbellifers, thistles and ragwort. The red-tipped Malachius bipustulatus and the slender Oedemera nobilis, both metallic green, are more characteristic of low-growing flowers such as buttercups. The brilliant reflective scarlet of the Commons’ two species of cardinal beetle ( Pyrochroa coccinea and P. serraticornis) render them instantly noticeable, whether they are visiting flowers, sitting on foliage or in flight. Many of the longhorn beetles, noted for their conspicuous antennae, are strikingly coloured or patterned, flying on sunny days and feeding at brambles and other flowers. They include the yellow and black Wasp Beetle ( Clytus arietis) and Spotted Longhorn ( Strangalia maculata), and two larger orange and black species, S. quadrifasciata and the rare and impressive S. aurulenta.

Page last updated: 22/01/07