Are they Blackflies or Sandflies? (Simuliidae)
In New Zealand they are called Sandflies or Te namu, however worldwide the Simuliidae are known as Blackflies. Simuliids of New Zealand belong to the genus Austrosimulium known only from New Zealand, Tasmania, and mainland Australia. In Australia there is an additional subgenus Novaustrosimulium. The nearest relative is the genus Paraustrosimulium in South America.
There are 19 simuliid species resident in New Zealand, three of these bite humans: the New Zealand Blackfly (Austrosimulium australense) found in the North Island and coastal areas of the South Island, the West Coast Blackfly (A. ungulatum) found in the South Island and abundant in Westland and Fiordland, and A. tillyardianum which can be found on both islands, although not in great numbers and generally only south of Auckland, mainly in the north and south through Canterbury.
A. ungulatum is the most abundant species, the females of A. ungulatum will fly long distances to obtain a blood meal. Indeed, searching along beaches for a blood meal from either birds or seals is probably the reason for their name “sandflies”.
These three species are very similar in size (approximately 2-3mm in length) and it is difficult to distuinguish them without a microscope. The ungulatum species-group has a basal tooth on the tarsal claws of the female while it is absent in the australense species-group. Elsewhere in the world those possessing the tooth are normally known as bird feeders, whereas those lacking the tooth are normally more mammophilic.
Blackflies occur in areas near water and humid bush, for example at beaches, lakes, rivers and swamps as they breed in running water. Only the females bite, as they require blood to produce eggs. Females that do not take a blood meal can still lay a smaller number of eggs, whereas blood fed they can lay up to three hundred eggs two to three times in their life cycle. The blackflies copulate only once in a lifetime storing the male sperm that re-fertilizes each new batch of eggs. The eggs are laid in running water clinging to mud, rocks or vegetation and take about ten days to hatch into small larva. The larvae attach themselves to vegetation or rocks in calm flowing water. They extend a set of fans that filter the flowing water which they feed upon. They form a cocoon of silk where the larvae develop into adult flies.
The blackfly density typically has a slight reduction in numbers during July and August and tend to be the most vicious on cool, windless days just before dusk and after dawn.They thrive in humidity above 60% commonly before it rains.
Worldwide, simuliids are notorious for their disease transmission, in particular onchocerciasis or river blindness, in Africa and South America, but more widely for the nuisance value of their bites, especially in the northern Hemisphere.
New Zealand simuliids are opportunistic and females will generally take blood meals from whatever is available. However the Fiordland crested penguins are heavily attacked by A. dumbletoni, a toothed-clawed member of the ungulatum species-group, as the females studiously avoid biting humans. The simuliids that attack penguins are a known vector for a bird “malaria”, Leucocytozoon, but are not known to be a vector for any human diseases.
The bites cause a subsequent itchiness, redness and swelling, caused by piercing the skin with a mouth shaped like a bread knife. The females drool while they lick up the blood pool. This drool contains a powerful anti coagulant called histamine that prevents the blood from clotting. Agglutinins that prepare the pooled blood for digestion are also deposited on the skin. It is this histamine and agglutinins mix that causes the red bumpy reaction in the victim's skin. The reactions will vary between people. The effects of the bites can be present for any period ranging from a few days to several weeks depending on the severity of the reaction and secondary infection may occur.
It is most common to apply an antihistamine cream or calamine lotion to soothe the affected areas, or for a severe reaction an antihistamine pill may be required. It is highly recommended to wear long clothes and apply repellent if exposed to a blackfly breeding area to avoid being bitten.
Austrosimulium sp. Photo by P. Bendle