Biting midges are often associated with estuarine wetlands
Biting midges are a group of biting flies that belong to the family Ceratopogonidae. The most significant pest species in Australia are Culicoides
ornatus and C. molestus, although other species can become pests when environmental conditions are favourable. Adult biting midges are typically
very small (usually less than 4 mm long) and a dark colour. They are characteristically stocky and the pest species often have a distinctive
pattern on their wings. Many species are not pests of humans, but some can transmit infectious diseases to cattle and sheep, and are of veterinary
Biting midges are commonly called 'sand flies' but, strictly speaking, sand flies are a group of biting insects in the subfamily Phlebotominae.
Sand flies are significant pests and vectors of human disease in other countries, but not in Australia.
Biology and ecology
Immature midges develop in moist conditions, including wet soil or organic detritus (e.g. leaf litter), feeding on organic material. Their life
cycle takes up to 10 weeks, depending on the climate, and the adults of some species can fly far from their larval habitats. Adult females
require a blood meal for egg development.
As a group, biting midges can live in a range of aquatic and semi-aquatic habitats, from estuarine environments to freshwater conditions. The major
pest species typically live within the tidal zone and sandy foreshores of rivers and estuaries, and generations of midges are often associated
with tide cycles. Coastal developments, such as canal estates, provide favourable conditions for biting midges, but they can sometimes reach
pest levels in other coastal and inland environments as well.
Public health importance
Biting midges do not transmit disease-causing microorganisms to humans. However, the nuisance biting of these tiny insects can be severe, especially
in areas near coastal lagoons, estuaries and wetlands. Anecdotally, biting midges cause more severe skin irritation than other common biting
pests, such as mosquitoes. Reactions to midge bites vary in severity, but there is usually swelling at the bite site, with redness extending
a centimetre or more around a central blister. The bites can be extremely itchy and may persist for some days. People living in areas where
biting midges are common may become desensitised, so the severity of reactions to bites can decrease over time.
A common myth associated with biting midges is that their urine causes the skin irritation. However, like other bloodsucking insects, midges inject
their saliva into the host during blood feeding and this causes an allergic reaction in humans.
There is no specific treatment for biting midge bites. As for other insect bites, a cold compress and soothing lotions or creams will reduce mild
reactions. Antihistamines may be required for severe reactions. Take care to avoid secondary infection after scratching the bites.
Personal insect repellents can offer some protection against biting midges. However, in areas with high midge populations, long-sleeved shirts,
long pants and head nets provide the most effective protection, especially if they are impregnated with insecticides (e.g. permethrin). Biting
midges are most active at dawn and dusk, so avoiding known midge habitats at these times will minimise exposure. In areas where estuarine biting
midge species are present, biting is likely to be greatest close to mangroves and in sheltered areas within 2 km of mangroves.
To reduce the number of midges in homes, ensure that buildings have adequate screens on doors and windows. The mesh of the screens must be small
enough to exclude these tiny insects (normal fly or mosquito mesh may not be small enough) or the screen should be treated with a long-lasting
residual insecticide. Properties with dense vegetation, especially shrubs, are more likely to be affected by biting midges, as the plants provide
some refuge and shelter for the midges. Generally, biting midge effects are greatest at ground level and the severity of nuisance biting decreases
at higher levels of a building.
Managing the pest and its impacts
Unfortunately, there are very few cost-effective and environmentally friendly options to control biting midges. As the main larval habitats of
the most common pest species are in environmentally sensitive estuarine habitats, local authorities cannot apply insecticide or modify the
habitat to carry out large-scale control. In most areas of Australia, larvicides are used in canal estates or other habitats close to houses
that may not have a high environmental conservation value.
Barrier treatments that protect residential properties close to biting midge habitats are common. These treatments involve applying a residual
insecticide to the outside of houses or surrounding vegetation. While this does reduce local biting midge populations, the nontarget impacts
should also be considered, such as effects on bees, moths, butterflies and other insects that may contact treated surfaces, as well as on aquatic
vertebrates and invertebrates, should the insecticides run into waterways.
Source: Australian Government Department of Health