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Beetles (Order: Coleoptera)

A photograph of male and female stag beetles (_Lucanus cervus_).

Possibly the most well known of Britain's beetles, the Stag beetle Lucanus cervus. The males have large 'antlers' and this gives them their common name. The smaller female does not possess large antlers.

Introduction

The Order Coleoptera or beetles forms the largest group of insects worldwide with about 370,000 described species. In addition many others have been recognised as new but have not yet been described and a conservative estimate is that at least the same number are still awaiting discovery. For these reasons it is impossible to estimate the true number of beetle species in the world.

However, the situation in the British Isles is slightly different and beetle diversity comes third with about 4,100 species, being surpassed by both Diptera (flies) and Hymenoptera (bees, wasps, ants, etc.).

General features

Beetles belong to the Endopterygota or insects having a complete metamorphosis, with a distinct pupal stage between the larval and sexually mature adult stages. A high proportion of beetle species are able to fly and these possess two pairs of wings. In most species the forewings or elytra consist of a pair of hard shells that protect the membranous hindwings which are normally folded away, but hinge outwards during flight. Flightless species may have reduced hindwings concealed beneath normal elytra or sometimes the elytra are fused together with no hindwings at all.

Beetles can be found in almost every imaginable terrestrial or aquatic habitat but many more species are found in tropical countries than in places with more temperate climates. Continental land masses tend to be richer in beetles than isolated islands, although these often support unique communities of species. Some species live deep underground in caves and a few are even able to survive in the inter-tidal zone along the seashore. There is enormous variation in size, body mass and form, the smallest adults being less than 1mm long and the largest about 20cm. Some longhorn species possess enormously long antennae, the variety is almost endless.

Special features

A number of beetle species are dependant upon other insects for their survival. For example, some ground beetles (Carabidae) are known to be parasitic on the early stages of other beetles - sometimes just one particular species. Other beetles breed in the nests of various Hymenoptera (bees, wasps and ants).

Collecting and studying beetles

To study most families of beetles it is necessary to collect a few specimens and make a reference collection. This is because many beetles need to be examined under a microscope in order for them to be identified.

Setting

Should a reference collection be required, there are several ways of preparing beetle specimens for permanent storage. The method chosen is partly one of personal preference but much depends on the beetle group chosen for study. The aim should always be to display the most essential characters needed for identification purposes. Large specimens may be direct-pinned by passing a stainless steel pin through the right elytron about one third from its base. It is best to fix smaller specimens onto specially manufactured white card mounts, with antennae and legs arranged symmetrically, using a water-soluble gum.

Although a certain degree of neatness helps when comparing one species of beetle with another it is not essential to 'set' specimens perfectly but the degree of neatness is a decision each entomologist must make. Gum tragacanth or any clear water soluable gum is equally suitable (the AES links directory has a list of entomological equipment suppliers). The latest edition of The Coleopterist's Handbook provides all the essential information required.

Identification

Beetles can be identified by referring to keys in a range of excellent books currently available. If a book on a particular family is out of print it is often possible to obtain a second-hand copy. Many dealers have searchable web sites for this purpose. With a little experience it is possible to identify specimens to family, and often genus level on site. This greatly speeds up the identification process. It is also suggested that Web sites with a good photo galleries, e.g., The Coleopterist are visited.

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