This is a predatory species, like all other British water beetles. Adults emerge at the end of June from pupae at the base of tussocks of rushes. The larvae feed on other aquatic insects and their young, such as water boatmen. Adults can fly and they may spend winters away from water altogether, whereas the larvae prefer open water.
The spangled water beetle has two subspecies where it occurs in Europe. One variety G. z. verrucifer is found in the northern regions as far south as Italy. The subspecies that occurs in the UK ranges through central and southern Europe as far as Mongolia. The UK range is limited to just one site, Wolmer Forest in Hampshire. In the past, this species was misidentified as a related species G. cinereus, and given a range that included Norfolk and the Cambridgeshire and Huntingdonshire Fens.
The spangled water beetle is found in several pools within Wolmer Forest, all of which vary considerably in depth, vegetation and acidity levels. The chief breeding area, however, seems to be concentrated in just one; Cranmer Pond. These pools have changed considerably over the centuries as a result of peat cutting, military activities and conservation work for natterjack toads.
In his collection of letters to Thomas Pennant and the Honourable Daines Barrington, published as 'The Natural History of Selbourne', the Reverend Gilbert White has left us with a description of Wolmer Forest and its ponds from around 1770. He describes the forest as 'without one standing tree in the whole extent', but more importantly he describes the ponds of Wolmer as 'stocked with carp, tench, eels and perch: but the fish do not thrive well, because the water is hungry, and the bottoms are a naked sand'. Today, these pools contain no fish at all.
This species is threatened by the loss, or mis-management, of their only known UK habitat, and by pollution from a nearby pig farm. There is also the possibility that changes in the acidity levels of their ponds could allow fish to return.
The spangled water beetle is listed in the UK Biodiversity Action Plans, and included in English Nature's Species Recovery Programme. Because of the precarious nature of this species' survival in Britain, annual monitoring of the ponds at Wolmer has been carried out since 1993.
All the currently populated ponds are now part of a Site of Special Scientific Interest (SSSI) and managed jointly by English Nature and the Ministry of Defence. It is planned to excavate four new ponds within Wolmer Forest in the hope that the beetle can increase its numbers. There has already been an attempt at introducing the species into a suitable new area but without success. Future work will include finding out more about the exacting requirements of the beetle so that any further introductions will, hopefully, be more successful.
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