New Zealand Sandflies

If you have ever spent more than two minutes outside in the summer sun while vacationing in the south island of New Zealand, you probably have become well acquainted with the sandfly. Having spent almost three months living in Milford Sound, I can say without any doubt that these little fellas have become a close part of my daily life. That is to say, they are the reason why I try to minimize my time outside during the day, and why, when I am outside, I am constantly speed-walking in circles while flailing my arms spastically. Here is some general information about the sandfly:


Introduction
The sandfly (“namu” in Māori) is the regional common name New Zealanders refer to two species of black fly: the New Zealand blackfly (Austrosimulium australense), and the West Coast blackfly (Austrosimulium ungulatum). At only 2–3mm in length, they look the same to the naked eye. The common name, “sandfly,” originates back to the voyages of Captain Cook between 1769 and 1775. The earliest known written reference of the name dates back to March, 1773 at which time, Captain Cook’s ship, Resolution, was anchored in Dusky Bay on the south-western tip of New Zealand. During their six-week stay, Cook and his men suffered miserably. The common name, “black fly” is thought to have North American origin.


Life-cycle
Sandflies, like mosquitoes and other flies, are members of the order Diptera, and belong to the family Simuliidae. Like mosquitoes, sandfly females bite because they need blood to get sufficient nutrition to produce eggs. Males are vegetarians. Also like mosquitoes, sandflies reproduce in water, which is why their numbers are worse near beaches, and at the edges of lakes, rivers, or swamps. There is one main difference between sandflies and mosquitoes, though: sandfly larvae require swift flowing water to survive because of how they eat. Sandfly eggs are laid on rocks or plants near or below the water surface. When they hatch, the larvae form masses fixed to the surfaces of submerged stones. They feed by catching morsels of organic particles, algae, and bacteria as it flows by. Generally, the duration of development from egg to fly averages six to seven weeks, of which 12 days are spent as the pupa.



Sandfly Behavior
Light intensity is the most important factor for sandflies to detect their hosts. Consequently, their numbers diminish as the sun goes down, and they nearly vanish at night. They seldom go indoors unless the room is lit well enough. Sandflies bite from dawn to dusk, but seldom at the same frequency throughout the day. During the day, morning peak numbers come from young sandflies that have recently emerged from pupae, and the higher evening numbers are often the result of sandflies taking blood after laying eggs earlier in the day. Higher activity can be conjured after a heavy rainstorm has depressed biting. Sandflies mostly thrive during overcast, calm, humid days. On these types of days, sandfly numbers are consistently high all day long. Their activity is high before rain, but is suppressed by strong wind. A sudden change in atmospheric pressure, like that seen before a thunderstorm, provokes increased biting activity.


Biting
Sandflies don’t suck blood like mosquitoes do. Instead, they use teeth to cut into the skin and feed from the bleeding well they create. The saliva of sandflies contains anticoagulants which are injected into the wound to keep the blood flowing. It also contains agglutinins that help prepare the blood for digestion in the fly’s stomach. It is these contents of the saliva that cause an allergic reaction in the skin characterized by itching, redness, pain, and swelling. This reaction is made worse by rubbing and scratching, but can be somewhat relieved with antihisamine cream or calamine lotion. Although the bites are quite annoying (and far more irritating than mosquito bites), they don’t do any long lasting damage or transmit disease in humans.


Detecting their Hosts
Sandflies find their hosts by detecting their profile, breath, odor, movement, size, shape, shininess, and temperature. The color and shininess of skin and clothing attract sandflies. Black, blue, and red seem to be the most attractive followed by brown, purple, maroon, and dark green. White, yellow, mid-grey, and green are not as attractive. Matt surfaces are more attractive than glossy ones. The fact that sandflies appeal to shaded parts of a host is a response to their attraction to dark colors. Smell is secondary to sight in detecting a potential host’s location. Carbon dioxide, octenol and other compounds that make up sweat and body odor appeal to sandflies.

I’ve noticed that sandflies love to bite you on your hands, arms, ankles, and feet. They particularly focus on the worse areas to be bitten: knuckles, wrists, elbows, and on the underside of your forearms. Bites in such areas are constantly irritated as you move throughout your day. These areas work out well for them because there is minimal hair to climb on, which gives away their presence (swat!). It is also possible that you give off more chemical indicators in these areas.


Preventing Bites
The best way to prevent bites is to cover up. Insect repellent works as well, but don’t stop biting completely. I find that DEET works over botanical repellents.

A sign in a shop window in Karamea on the West Coast of New Zealand explains another great sandfly remedy:

Purchase a bottle of good quality whisky.
Rub liberally on arms and legs.
Dust sand on skin whilst still wet with whisky.
The sandflies come along, get drunk, and throw rocks at each other.

It’s worth a shot!