During a recent survey of a pond at Castle Water we found man Emperor larvae at various stages of development, but the highlight was finding three fully grown (final instar) Red-veined Darter larvae.

The Red-veined Darter is a highly migratory species which is resident in the Mediterranean countries of Europe, arriving in Britain pretty much annually as an immigrant. This species is capable of producing two generations a year because the larvae develop in three months compared to a year, which is typical of other darter species in Britain. So migrants arriving here in early summer can produce an emerging population in late summer.

Evidence of breeding has been confirmed on the reserve on two previous occasions (2007 and 2008), and on the second occasion a larva had successfully overwintered. The British winters are one reason why resident populations have seldom been sustained. After the discovery this year, the pond was checked on a daily basis to establish how big the emerging population was. Several exuviae (shed larval skins) were found, plus one emerging adult. It is possible that larvae are still present in the pond attempting to overwinter, these would emerge next spring. It would be great if this species could manage to establish a permanent population on the reserve.

Sam Smith