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Guide to New Zealand's freshwater invertebrates
Rat tail maggots
The syrphid larva has a maggot-like body with a long tail-like breathing tube.
The breathing tube allows syrphids to live in waters with almost no oxygen. Such conditions might exist immediately below long-term discharges of organic waste such as silage pit leachate, dairy waste or sewage.
They eat decaying organic matter, hence their occurrence in waters with a long term supply of organic waste.
The presence of syrphids in any stream indicates firstly that you shouldn’t be coming into contact with the water, and secondly you should be calling your local pollution hotline as syrphids are a sign of a serious pollution problem. Syrphids have tolerance values of 1 (hard bottom sites) and 1.6 (soft bottom sites) reflecting their association with heavily polluted waters.