Friday, 2 August 2013

A high summer midge hatch

High summer time ponds can be slightly disappointing for their animal life as the larvae and juveniles of so many insects which thronged the ponds in April and May hatch and fly out to become, often very briefly, terrestrial. The productivity of the ponds is a subsidy to the food webs of wider landscape. For a few species such as dragonflies and damselflies the glamorous and gaudy adults are a much admired addition to the sights of summer. Along Druridge Bay Blue Tailed damselflies (Ischnura elegans) and Common Blue damselflies (Enallagma cyathigerum) are particularly widespread and Southern hawker dragonflies (Aeschna cyanea) are also beginning to patrol some of the hedgerows and lanes. Few of the other insect life hatching from the pools attracts much interest or favour, instead mostly complaints as various midges and mosquitoes fidget around us. The shallow ponds and flashes in the arable fields are particularly good for some midges, members of the Chironomidae Family (non biting midges). The particular species that are most obvious are from the genus Chironomus, conspicuously red, and wiggling in a slightly lazy figure of eight if you stir the mud. Individually they seem small and perhaps insignificant, but the photo above shows a wind-blown line of their discarded pupa cases, left behind as the adults emerge. The open rims  of the cases, split along the back where the adult hauled itself out, are water repellent, hence the sharp edges. Thousands have made it from the muddy field pond. These temporary sites are seldom colonised by predators such as diving beetles of sticklebacks which can exterminate these midges. Ducks and waders take a toll, leaving their prints in the mud, but the midges still hatch in their thousands. The midges themselves feed on fine particles of organic debris and algae which they scrape and graze. The ponds can show vivid mats of algae carpeting the mud, the whole pond briefly very productive for the few creatures that can cope with the urgency to hatch, grow and mature before the water dries out. The midges make ideal food for dragonflies too