Sandflies: New Zealand's blood-sucking summer nightmare (actually, it's year-round)

A biting sandfly enjoying a ''blood meal''.
Landcare Research

A biting sandfly enjoying a ''blood meal''.

Most outdoorsy types have a horror story.

New Zealand explorers were often driven to distraction, Maori in the South Island knew all about them, and European settlers apparently smothered themselves with rancid bacon fat as a deterrent.

Mine was at the head of the Hollyford, in Martins Bay, as clouds of beasties swirled so thick they got in my mouth.

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Stunning Martins Bay, Fiordland. From here, the sandflies aren't visible.

Stunning Martins Bay, Fiordland. From here, the sandflies aren't visible.

They tear at our skin, using saw-like barbs to widen tiny wounds, and suck our blood. (Really, that's how they feed).

Yes, it's the humble New Zealand blackfly, commonly known as the sandfly.

On occasion, the bites cause nasty swelling, itching, hives, and a general desire to scream.

At their worst, in the most intense sandfly-ridden spots of the West Coast, entomologists have recorded a bite rate of up to 1000-an-hour. In a couple of minutes, that could be hundreds of little bites, on your arms, neck, face, feet.

Sandflies, on a minute level, rip and tear the flesh to open the skin and access blood, using anti-coagulating qualities of saliva to feed. It's histamine that causes the itching and swelling.

Entomologist Trevor Crosby is a co-author of an authoritative study of sandflies in the Fauna of New Zealand series for Landcare Research.

He said the name probably derives from Captain Cook's reference to "mischievous animals" that caused pox-like ulcers in Dusky Sound in 1773.

HUMAN BAIT

Crosby has acted as human bait in the past to study sandfly bite rates.

Entomologist Trevor Crosby, who has acted as human sandfly bait in the name of science.
Sally Tagg

Entomologist Trevor Crosby, who has acted as human sandfly bait in the name of science.

"It's only the females that bite and there are three main species that bite humans. One of the species is throughout New Zealand, the other two species are only in the South Island, the ones that really bite.

"The worst biter, that's Austrosimulium ungulatum, that's not found in the North Island.

"What we complain about are the biting females."

The head of a female New Zealand sandfly.
Landcare Research/Fauna of New Zealand

The head of a female New Zealand sandfly.

Ask anyone who has visited the West Coast of the South Island and they will probably have something to say about sandflies.

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Crosby said sandflies evolved to prefer penguins as a "blood meal" (that's the technical term) over humans but, in the absence of tasty penguins, sandflies are particularly attracted to people.

Why?

Entomologists don't have enough information to explain this.

"I don't know whether we are a preferred host. Individuals react differently. That probably indicates the scent of people and maybe their clothes and how much CO2 they give off.

"Again there's a lot of mystery there as to what's attracting them.

"Dark colours seem to be more attractive to them than light colours. I think what's interesting is that a species comes to humans [but] where there are penguins we've stood there and watched the species fly straight past us to get to the penguin. They prefer penguins."

REMEDIES

People react differently, some people erupt in hives and intense itchiness, but - again - there have been very few studies on why humans react so differently to bites.

​Using tiny claws and a proboscis-like mouth, sandflies stretch the skin to make it taut and use mandibles to tear and saw through the tightened skin. An anti-coagulant in their saliva helps the blood pool and histamine causes itching.

"What they inject into you causes a bit of numbness but it's not as evolved as some overseas species that can bite and you don't feel it. They have hooks that push the skin and use the mandibles to cut through.

"The New Zealand species is different. Once they've cut it they have these little spear-like little saw hooks to deepen the wound and make a little pool of blood. They need the blood to mature their eggs," Crosby said.

Female West Coast sandfly claws. The scale bar is 0.2mm.
Landcare Research

Female West Coast sandfly claws. The scale bar is 0.2mm.

They can breed year-round, and in the early stages of their waterborne cycle, they help purify the surrounding water. 

"We're fortunate that they are not known to carry any diseases of humans. They are a pain but there's no disease. There's one disease, a malaria-like blood parasite, carried to the Fiordland crested penguin," Crosby said.

Remedies?

There are many, but even the hardiest prophylactic often fails and, somehow, one of the insects gets into your tent, or your car.

DEET can be effective, but many people don't like using it, and there are lots of natural remedies available. Sandflies do not like rain, or smoke.

One home remedy involves a mix of Dettol and baby oil, others reckon garlic, or Vegemite does the trick.

Theoretically then, one way to deter sandflies is to walk around carrying a penguin as bait, while eating garlic, covered in Dettol and baby oil. That might raise eyebrows as penguins are protected, so best not.

Captain James Cook, who described sandflies as ''the most mischievous animal''.
FILE

Captain James Cook, who described sandflies as ''the most mischievous animal''.

TRAMPING TIP

Crosby has one tip.

"When you're out tramping, if you want to have a rest, most people stop on the edges of clearings between the trees or a grassy area. That's where they congregate. [If you're building] it's best to be in the middle of a bleak field with a cleared area."

Travel journalist Siobhan Downes' sandfly-bitten feet. She did not get along with the West Coast sandflies and was ...

Travel journalist Siobhan Downes' sandfly-bitten feet. She did not get along with the West Coast sandflies and was interviewed about her ordeal by a local newspaper.

Christchurch-based travel blogger Lis de Brauwer​ said she had not managed to find any effective remedy except covering up.

"Apparently if you get bitten enough you'll eventually get used to it.

"But I don't really like that strategy, so I just cover my skin with clothing. That works, but can be annoying when it is a hot day."

A model of a sandfly at the cafe on the West Coast.
Department of Conservation

A model of a sandfly at the cafe on the West Coast.

Maori inhabitants of the South Island had some plant-based deterrents and smoke was another method. Sandflies do not like wind, and are most numerous during daybreak and dusk in humid, overcast conditions, just before it rains.

The West Coast of the South Island, particularly Fiordland, is notorious.

Te Papa entomologist Dr Phil Sirvid​ said new species of invertebrate were being discovered all the time. New Zealand does not have any native invertebrate species capable of causing serious harm. The native katipo spider, although related to the black widow, is rare and its bite painful, but it's not life-threatening.

"We are in many senses of the word still an undiscovered country.

"We have mosquitoes that can carry potential vectors for certain species of disease. 

"We have a number of species imported from Australia. The potential is there - we are just lucky."

Entomological Society of New Zealand president Dr Cor Vink​ said there's simply not much to be done about sandflies.

"They interact with blue and they're attracted to warmth. There's not a great deal you can do about them other than the insect repellent you can put on.

"A mosquito has a pushing [mouth], it's long, a proboscis. These guys, they rip apart the flesh at a small level."

A Maori legend has it sandflies - namu - were created to prevent people lingering in beautiful parts of the country, and entomologists think birds were the main target for feeding before the arrival of Pacific voyagers.

There are more than a dozen native New Zealand species of sandfly, but only three species bite. 

The Landcare Research series on the fauna of New Zealand by Prof Crosby and Canadian entomologists Douglas Craig and Ruth Craig says almost every New Zealander and most tourists have been bitten at some stage in their lives.

In the North Island, the main offender is the Australian black fly - Austrosimulium australense - but the insect that really gives the species its reputation is the West Coast blackfly, A. ungulatum.

​"The females of A.ungulatum will fly long distances to obtain a blood meal and their ferocity has generated many horror stories from early settlers and more recently the annual million or so overseas tourists. Few of the latter leave New Zealand unscathed if they visit Fiordland."

They get through clothes, in your hair, inside your tent.

Stop for a sandwich break at the side of a road and they divebomb you.

They need running water to breed but they go away at night because they can't see in the dark so after a tramp or a visit to the beach battling clouds of the toothsome little biters, you can at last get some rest.

Captain Cook, by the way, did not take long to notice them at Dusky Sound in 1773.

"The most mischievous animal here is the small black sandfly which are exceeding numerous...wherever they light they cause a swelling and such intolerable itching that it is not possible to refrain from scratching and at last ends in ulcers like the small Pox," wrote Cook, according to the Encyclopedia of New Zealand.

Do you have a horror story involving sandflies? Share your misery in the comments.

 - Stuff

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