The native midge (Chironomus zealandicus) is a small fly, similar in appearance to its close cousin the mosquito. During the warmer summer months the adult flies can form large swarms, which can reach nuisance proportions.
The native midge has always lived in the still, fresh waters near the Avon-Heathcote Estuary. Lake Ellesmere, Lake Forsyth, and around Horseshoe Lake are also common breeding spots of the midge. The oxidation ponds at the Christchurch Wastewater Treatment Plant have become an ideal breeding site, with their nature as a wastewater treatment process creating an imbalanced ecosystem that favours one species over another – in this case midges.
The midge lays its eggs directly into shallow freshwater pools and may attach them to plants or stones at the water's edge. They have a 20 to 40 day lifecycle (depending on water temperature) and only spend two to three days as adults, during which time they mate and breed.
Adult midges require water temperatures greater than 17 degrees for optimal breeding. During autumn and winter they become dormant.