Tuesday, February 7, 2012

Plague of Midges Caused by Quake?

Adult lake fly midge
Those living or working close to the Christchurch sewerage settlement ponds will be aware of the large numbers of lake flies (New Zealand midges Chironomus zealandicus) that are about at the moment.

Lake flies are often mistaken for mosquitoes but in fact are not closely related and they do not bite. They cannot bite because they do not have mouth parts. These adult flies have a short life in this stage, seeking a mate, laying eggs back in still water and then dieing after only about 36 hours as adults.

The larvae of these flies live in still water such as lakes, slow rivers and settlement ponds. The larvae, which are wriggly, worm-like and red are known as 'blood-worms.' They live in the mud at the bottom of the water where they feed on micro-organisms. The Christchurch and Auckland settlement ponds and lakes such as Lake Ellesmere are well known for producing plagues of midges in summer. This year is particularly bad around the Christchurch settlement ponds probably because of the disruption to the ponds in the Canterbury quakes. The quakes have caused disruption of the pond mud and damage to the Christchurch sewerage system has brought high levels of nutrient in to the ponds where the micro-organisms on which the midge larvae feed have been in bloom.

Midges covering building surfaces
Because these insects do not bite they are only a nuisance pest. But they can be a considerable nuisance. They will rest and hide in vegetation and on buildings around their breeding sites. Numbers can be such that as one walks past and disturbs them they lift off and will stick in hair and can be breathed in. This is rather unpleasant as I well know. Kiwicare is within a kilometer of the Christchurch settlement ponds and the building is covered with midges. The shrubs in the car park are also full of hiding insects. Each time I open the boot of my car a cloud of flies is disturbed and I have had to spit one or two out. There is also a carpet of dead ones building up in the car park. If the problem gets much worse I will have to spray the exterior of the building with NO Bugs Super to reduce the numbers. It will not get rid of them all as there is such a rapid turnover of numbers but it will help to make the place more pleasant to work around.

What did the NZ midge say to the mosquito?
Nothing. Without a mouth it was speechless.

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