If you get bitten by tiny black flies it is likely that you have been the victim of what New Zealanders call sandflies (namu in Māori). Sandflies, like mosquitoes and other flies, are members of the order Diptera, and belong to the family Simuliidae. Similar species found elsewhere are called blackflies.
There are 13 species in New Zealand, all belonging to the genus Austrosimulium. Only two species bite: the New Zealand blackfly (Austrosimulium australense), and the West Coast blackfly (A. ungulatum). At only 2–3 millimetres in length, they look the same to the naked eye.
Sandflies are found wherever there is flowing water and bush. They are often found at beaches, and at the edges of lakes or swamps. The New Zealand blackfly occurs in the North Island and around the coasts of the South Island. The West Coast blackfly is confined to the South Island, where it is a nuisance.
The West Coast and Fiordland are infamous for their sandflies. The terminus of the Milford Track, where trampers board the ferry to Milford Sound, is called Sandfly Point.
While surveying Doubtful Sound in the summer of 1851, Captain John Lort Stokes of the Acheron was tempted but resisted putting the names Venom Point, Sandfly Bay and Bloodsuckers Sound on the map, after encounters with the biting insects. Road builders on the Milford Road and Haast Pass suffered clouds of them. While surveying road routes near Haast in the 1930s, Alan Dawber played a game with his mates: ‘We used to compete with each other by baring our forearm to the sandflies, then when the first one made its presence felt, we would start killing them off one by one. I think the record was 64 before wiping the stinging mass clear.’ 1
Sandflies breed in fast-flowing streams or rivers. Eggs are laid on rocks or plants around or below water level. Larvae hatch and collect food from the current, using foldable ‘nets’ that surround their mouths. These expand to catch passing organic particles, algae, and bacteria. The larvae pupate and spend around 12 days in this form, before emerging as flies at the water’s surface.
The length of the life cycle varies, depending on the time of year, but averages around six to seven weeks.
The first instance of the word sandfly (rather than blackfly) for the New Zealand species is in the journal of James Cook. He came across the insects at Fiordland’s Dusky Sound, possibly at a sandy beach, in May 1773. His journal reads:
‘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.’ 2
After mating, the female searches for a meal of blood – needed to produce eggs. (Little is known about the male, who is a vegetarian.) Females attack vertebrates such as penguins and other birds, bats, seals, domestic animals and humans. They pierce the skin, creating a drop of blood that they suck up.
Sandflies cannot see at night, so they seldom bite in the dark, and generally remain outdoors. Peaks in biting often occur when light intensity increases in the morning and decreases at dusk. The morning peak comes from young sandflies that have recently emerged from pupae, and the higher evening peak is often the result of sandflies taking blood after laying eggs earlier in the day.
Sandflies are most active in dull, overcast and humid conditions, when they may bite at a similar rate throughout the day.
New Zealand has 16 species of mosquito, known to Māori as waeroa. Twelve are endemic (unique to New Zealand) and four are introduced. They are about 5 millimetres long and, as with sandflies, only the female bites (the males feed on flower nectar). Some areas – especially around swamps – are notorious for their swarms. One site north of Haast, on the West Coast, is called Mosquito Hill.
In her book Through South Westland (1911), traveller Maud Moreland described a desperately uncomfortable night in the Blue River Hut. She and her companion slept little and in the morning their hands and faces were swollen. Today, tramping huts in such blighted areas often have insect mesh over any opening windows.
Very little is known about New Zealand’s mosquitoes, and much of the current knowledge is anecdotal and speculative. Most of the 12 native species of mosquito seem to primarily feed on birds, although some species bit humans, especially Coquillettidia iracunda.
The other biting species are Culiseta tonnoiri and Aedes antipodeus.
The most common native species is the vigilant mosquito (Culex pervigilans). It is commonly found around Auckland city, where it enters houses. A night-time feeder, its high-pitched buzzing and biting can disturb the sleep, although it rarely bites humans. The larvae are likely to be found in any container that collects rainwater, such as old tins or bottles. The larvae are known as ‘wrigglers’, as they often wriggle to the surface to breathe.
The remaining five endemic species are reasonably widespread throughout New Zealand.
There are four introduced mosquito species. Three of them regularly bite humans.
Named for the white bands on its legs, the silent striped mosquito (Aedes notoscriptus) was first noted in Auckland in 1916 and probably arrived from Australia. It is the mosquito most often seen in the North Island and females may bite during the day and at night. In the South Island the species is thought to occur only in Nelson, Marlborough and Christchurch.
The brown house mosquito (Culex quinquefasciatus) is native to warmer parts of the Americas. It is thought to have arrived via the water supplies of American whaling ships, probably in the 1830s. It is found around North Island ports and occurs as far south as Marlborough. It readily bites people, and lays its eggs in standing water around houses (for example, in guttering, bird baths and septic tanks).
New Zealand only has 13 sandfly and 12 mosquito species that are native. Similar-sized countries with temperate climates have more: Japan has 65 species of blackfly (sandfly), and 67 mosquito species; England has 32 species of mosquito. The reason may be New Zealand’s evolutionary history – there were no land mammals apart from a few bat species. In other lands, there were many large mammals for blood-sucking insects to feed on.
The southern saltmarsh mosquito (Aedes camptorhynchus) arrived around 1998. It was first found in swamp land near Napier, after complaints of its vicious biting. In its native Australia, this species can carry the Ross River virus and other diseases. Despite an eradication campaign, the insects have shown up in other parts of Hawke’s Bay, and in Gisborne, Northland and Marlborough. Eradication seems to have been successful in Napier, and similar schemes are in place in other areas.
The saltwater mosquito (Aedes australis) probably arrived at southern New Zealand ports on timber ships from Australia. It was first recorded in Stewart Island in 1961, and is also found in Southland, Otago and Westland. As this species does not stray far from coastal rock pools, it does not often bite people. Females do not need a meal of blood in order to lay eggs.
Māori used crushed leaves of the ngaio tree (Myoporum laetum) to deter mosquitoes and sandflies. They also doused their bodies with oil, and with kōkōwai (red ochre) when working naked in the fields. To soothe itchy bites, they applied a juice made from crushed ngaio leaves or from fronds of rarauhe or bracken fern (Pteridium esculentum).
The simplest way to avoid bites is to cover up, especially when sitting or standing still – sandflies tend not to bite moving targets. They rarely bite indoors or after dark, and are not found above the bushline.
One of the best ways to reduce mosquito numbers around the house is to remove all standing water from clogged drains and elsewhere, as this is where they breed. When camping, cover up well, and avoid swampy areas. In mosquito-prone places, a fully enclosed tent with mesh screens is essential. Repellents should also be used.
West Coast gold miners rubbed rancid bacon on their skin in the 1860s. When the minister for public works, Richard Seddon, rode the track from Paringa to Haast in 1892 he coated himself with camphorated lard, which he deemed a success. Also effective are home-made concoctions of olive oil mixed with disinfectants such as Jeyes Fluid or Dettol. Citronella oil, used in sprays and candles, or in skin lotions, can help keep insects at bay.
Insect repellents for the skin are effective against sandflies and mosquitoes. The active ingredients in many repellents are known by the abbreviations DEET (diethyl toluamide) and DIMP (dimethyl phthalate). DEET is the most effective repellent. It has been used by millions of people worldwide since 1957, and has a very good safety record. It is recommended that repellents used on children contain less than 10% DEET.
Many people believe you can repel sandflies or mosquitoes by swallowing garlic or vitamin B (for instance in the sandwich spread Vegemite), or drinking beer from a flagon to which a capful of kerosene has been added. But there is no evidence that anything taken orally works against these insects.
All repellents need to be regularly reapplied. DEET-based products are typically effective for one to six hours.
Sandfly and mosquito saliva contains anticoagulants (to keep blood flowing) and agglutinins (to prepare blood for digestion). These cause allergic reactions such as itching, redness and swelling. Reactions vary, and compared to newcomers, local people seem to be less bothered by sandfly bites. As they have been bitten before, their bodies may not react as strongly to the proteins in sandfly saliva.
Sandfly and mosquito bites should not be rubbed or scratched, as this can inflame the bite and break the skin. Itching and swelling can be soothed by antihistamine cream or calamine lotion.
Although overseas species of blackfly can carry and transfer diseases, there are no records of New Zealand’s biting sandflies doing so. Nor have any mosquito-borne human diseases from a local source been recorded. Mosquitoes do transfer the Whataroa virus among birds on the West Coast, but this does not appear to kill or make birds ill.
Three introduced mosquitoes – the brown house mosquito, the saltwater mosquito and the striped mosquito – are able to transmit human and animal pathogens or parasites overseas. Four endemic species – Culex pervigilans, Opifex fuscus, Culiseta tonnoiri, Aedes antipodeus – may also carry and transmit diseases, but this is untested. Since the 1930s at least 30 species of exotic mosquito have been intercepted at New Zealand ports. Most of these can carry and transmit diseases.
Global warming will produce warmer temperatures throughout the country, and wetter conditions in its western regions. As temperatures increase, some mosquito species are likely to spread southwards, and there will be greater potential for exotic species to breed.
Acknowledgements to Paul Leisnham and José Derraik.
Belkin, John. Mosquito studies (Diptera, Culicidae). VII. The Culicidae of New Zealand. Ann Arbor: American Entomological Institute,1968.
Laird, Marshall. New Zealand’s mosquito fauna in 1995: history and status. Wellington: Ministry of Health, 1996.
Orr, Marjorie. Those sandflies. Whatamango Bay: Cape Catley, 1996.