Beetles

Identifying individual beetle species can be difficult, as there are so many inhabiting Britain’s fresh waters, but their behaviour can at least suggest whether they feed on plants or other animals - a slow-moving creature is unlikely to be a predator.

The plant-eaters include a group called the water scavenger beetles, whose largest member, the Great Silver Beetle, is Britain’s largest beetle. The silver appearance of this and other beetles in the group when in water is given by the air supply, carried from the surface as a layer on the body's under-surface and under the wing covers. While the adults feed on decaying plant remains and algae, the larvae are carnivores preying mainly on snails. The larvae surface rear-first to collect air through spiracles - these are the pores through which insects exchange gases with their environment, each species having a characteristic number and arrangement.

Among the carnivorous beetles are the diving beetles, of which the Great Diving Beetle is the most impressive. This is a fierce predator which can tackle creatures larger than itself - even small fish. The adult chews up and swallows its prey, while the larva injects its prey with digesting enzymes and sucks out the resulting "soup”. A diving beetle carries an air bubble under its wing covers, while its larva, like that of a water scavenger beetle, pokes its rear through the water’s surface to collect air.

Whirligig beetles are a familiar sight, living up to their name by whirling around at the water’s surface. The adult frequently takes advantage of insects stuck to the water surface, which it chews up, while the larva pierces and sucks its prey, often mosquito and midge larvae. A whirligig beetle dives when alarmed, carrying an air bubble stuck to its rear. Its larva has fringes of hair-like gills along the sides of its body.

Water Scavenger Beetle	Diving Beetle	Whirligig Beetle
[Adult 1-150mm, larva larger]	[Adult 2-38mm, larva larger]	[Adult 3-8mm, larva larger]

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