Amazing facts about sandflies

By Michelle Harnett

Summer in New Zealand: slip, slop, SLAP! The smear of red and black on your arm, leg or foot is blood and the remains of a sandfly (namu in Mäori).

Only three of the 19 Austrosimilium species identified to date bite humans but they cover the country from the far north to Bluff, avoiding only very dry areas of the South Island’s east coast.

A red smear means it’s too late, you have been bitten and the wound has been injected with
anticoagulants to keep the blood flowing and agglutinins to start the digestion process.

The familiar redness, swelling and itchiness of a sandfly bite is caused by an allergic reaction to these foreign substances.

Sandflies find their prey by detecting dark colours, changes in carbon dioxide concentration and odour.

To the West Coast sandfly the smell of humans is as enticing as that of moulting penguins, prompting the question, what did sandflies bite before humansarrived?

The answer is birds, seals and bats, which were present in far greater numbers than today.

Feeding on humans is opportunistic behaviour.

Only the females bite, seeking nutrients to produce eggs, which are laid on rocks in and around running water.

On hatching, the larvae spit out a silk that they use to stick themselves to stones. Safely attached, they extend fine fans around their mouths to filter food particles from the flowing water.

The larvae are in almost every waterway in New Zealand, providing a food source for birds, insects like the caddisfly and native fish – bullies, galaxiids, eels and mudfish.

Liberal use of insect repellent is the best way to avoid being bitten. Mäori are reported to have smeared their bodies with clay and fat to avoid bites.

Early settlers also favoured fat, sometimes mixed with kerosene or disinfectant. A chemical-free alternative is to cover up exposed skin with light-coloured clothes
and keep moving, especially on cloudy, humid days.

Or stay inside and only come out after dark, but that is hardly the way to enjoy summer.