Lesser silver water beetle (Hydrochara caraboides)

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Lesser silver water beetle
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Lesser silver water beetle fact file

Lesser silver water beetle description

KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderColeoptera
FamilyHydrophilidae
GenusHydrochara

This beetle earns the name 'silver' from the bubbles of air that are trapped in the fine hairs on its underside. These hairs form part of an elaborate breathing system, enabling these beetles to live underwater. The beetles' 'true' colour is shiny, polished black. They have well-developed 'palps', sensitive mouthparts, which act as preliminary tasters for food. Unlike the diving beetles, Dytiscidae, the silver water beetles are not particularly adapted for underwater life. They are poor swimmers, without the modified legs of diving beetles, and take air from the surface headfirst, rather than with the tip of the abdomen like many other water beetles.

Size
Body length: 15 mm
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Lesser silver water beetle biology

Eggs are laid in spring or early summer, and the larvae are often found from May to July, floating just below the surface. Adults are herbivores and feed on decaying plant matter, but the larvae are carnivores, and feed on water snails. The adult beetles emerge during the summer and hibernate, but it is not clear whether this occurs in the water or on land. The beetles are attracted to light, and are good fliers.

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Lesser silver water beetle range

This species is known only from the UK, and was widely distributed during the 19th century. However, since 1970, it had only been recorded in eleven 10km squares, with the only known breeding population in the Somerset Levels. Then, in 1990, an adult beetle was found in a pond in Cheshire. Since then, larvae have been found in several other ponds in the county as well as former sites on the Somerset Levels.

You can view distribution information for this species at the National Biodiversity Network Gateway.
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Lesser silver water beetle habitat

The adult lesser silver water beetle is found in still, weedy ditches and ponds in peat-rich areas. It seems to prefer deep water where there is little chance for the peat to dry out, and places subject to piecemeal disturbance. Recent research, however, suggests that the eggs and larvae are found in shallow, often temporary, ditches with overhanging tree cover.

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Lesser silver water beetle status

Classified as Endangered (UK), and protected under Schedule 5 of the Wildlife and Countryside Act, 1981.

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Lesser silver water beetle threats

It is believed the principal threats to the lesser silver water beetle is from inappropriate ditch management, and the loss of grazing marsh leading to re-profiling of the ditches.

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Lesser silver water beetle conservation

The lesser silver water beetle is listed in the UK Biodiversity Action Plans, and has been included in English Nature's Species Recovery Programme. As well as the UK action plans, this species is listed in at least two Local Biodiversity Action Plans (LBAPs) including Cheshire's 'Countdown' project and the Mendip Biodiversity Action Plan. Ponds on the Cheshire Plain have been subjects of the Pond Life Survey since 1995, and there is a comprehensive survey under way to establish the true status of the species in the county. Surveys for this species were also undertaken in 1993 and 1994 on the Somerset Moors, and the management of many of the beetles breeding ditches is now based on the conservation of this species. In the future, it is hoped that suitable breeding habitat for the beetles will be created by flooding wet woodland, producing shallow areas of water at the start of the beetles breeding season.

View information on this species at the UNEP World Conservation Monitoring Centre.
There may be further information about this species available via the National Biodiversity Network Gateway.
The UK Biodiversity Action Plan for this species is available at UK BAP.
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Authentication

Information supplied by English Nature.

http://www.english-nature.org.uk

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Glossary

Hibernate
A winter survival strategy characteristic of some mammals in which an animal's metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is 'diapause', a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.
Larvae
Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
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References

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Image credit

Lesser silver water beetle  
Lesser silver water beetle

© Roger Key

Dr Roger Key
Tel: +44 (0) 1845 567 292
key_r_s@yahoo.co.uk

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