Thursday, 10 November 2011

Lead beetles not always welcome

The Chrysomelids or leaf beetles are one of our more accessible groups of beetles. Most are rather colourful, many are relatively large in size and quite a few have an English name by which to refer to them. Although one of the largest beetle families worldwide, we have just 260 or so species here in Britain, some of which will already be familiar to farmers and gardeners as pests of agriculture, horticulture and forestry.

As the name suggests, leaf beetles feed on plant material, taken from a vast range of plant species, including ‘primitive’ plants like mosses and horsetails. Most show some degree of specialism, again highlighted in the name, for example: Rosemary Beetle (Lavender and Rosemary), Belladonna Flea Beetle (nightshades, Henbane and Thorn-apple) and Lily Beetle (lilies and fritillaries). The association with particular host plants may explain the seemingly steady arrival of species new to Britain, transported here on plants shipped around the globe to satisfy gardeners’ demands for the new and exotic. The Rosemary Beetle, a specimen of which was presented to me just the other day by a work colleague, is a recent arrival from the Mediterranean. First recorded from Surrey in 1963, it is now found in many counties across Britain.

Some of the larger Chrysolmelids, like Rosemary Beetle, are fairly long-lived (lasting two or more years). Others are interesting because of the ways in which they seek to avoid being eaten. The flea beetles, for example, have enlarged hind femora. These work in association with muscles to store energy that can be released with a spring-like action, catapulting the beetle away from danger. Some species feign death when disturbed, e.g. Lily Beetle, while others make a noise by rubbing two rough surfaces together in a stridulating action. Perhaps the most impressive forms of anti-predator device are deployed by the Bloody-nose beetles, who are able to deploy reflex bleeding from their joints. The ‘blood’ that emerges contains noxious and often toxic compounds which are quite enough to deter most would-be predators.

Many of the leaf beetles are capable of flight, taking to the wing on warm days. Mind you, perhaps with the exception of ladybirds and maybugs, we don’t tend to think of beetles as flying insects. This may be because their wings are so well concealed under the hard wing cases or elytra. Some of the leaf beetles are particularly good swimmers, with some species associated with waterside habitats. Again, this is a somewhat unexpected behavioural trait that is easily overlooked.

While the leaf beetles may be unwelcome by those of a horticultural bent, they are a fascinating group for the entomologist. Varied, colourful and sometimes unexpected in their habits.

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