New Zealand “sandflies”, of which less than 10 different species are known at the present time, are true simuliid flies. Without doubt they are one of the greatest nuisances to human beings and warm blooded animals in New Zealand because of their biting habits. They often invade houses provided the rooms are not too dark; they are never found in dense bush but only on the edges, in clearings, and in large open spaces; they prefer banks of lakes, sea beaches, or high tussock grassland areas up to 5,000 ft, which is their uppermost limit. Where the winter is mild, they occur throughout the year. Populations of adults can be very high and in preferred localities they appear in such large numbers as to create visible swarms. The adult female is an aggressive blood-sucker but the male is incapable of drawing blood. Females are only on the wing during the day but in summer they may be active after sunset in the twilight but not during the night. Sandflies have no medical significance as they are not known to carry any disease organism. Adult flies are about 2½ mm in length, dull, velvety black in colour, and characterised by their hunch-backed or buffalo-like appearance. The pre-adult stages are passed under water in streams and rivers.
by Roy Alexander Harrison, D.SC., Senior Lecturer in Agricultural Zoology, Lincoln Agricultural College.