March fly warning for Pilbara and Gascoyne regions

The Department of Health is warning residents and travellers across the Pilbara and Gascoyne regions to take extra care to avoid March flies, as a number of people have reported severe allergic reactions after being bitten by the insects.

WA Health’s Acting Medical Entomologist Dr Jay Nicholson said recent rainfall combined with warm temperatures has led to an increase in March fly breeding in some areas.

“This has been particularly evident around Roebourne, where several people have experienced severe reactions after being bitten,” he said.

“Although March flies are not known to transmit diseases to people in WA, bites can cause adverse allergic reactions, including skin redness and swelling.

“In rare cases, people may experience serious symptoms including hives, fever, wheezing, difficulty breathing and anaphylaxis.”

Dr Nicholson said painful bites could be treated with ice packs and mild anti-histamines. If bites become infected due to scratching, an antiseptic cream or antibiotic may be required.

“Individuals experiencing severe allergic reaction, such as widespread swelling or rash, or difficulty breathing should seek urgent medical attention”, he said.

March flies (also known as horse flies) are stout-bodied flies measuring 6-25mm in length, with large eyes and piercing mouthparts. There are more than 200 species and they can occur anywhere in WA, in a range of habitats. They are most active during daylight hours. The bite of one species in particular, found in northern WA, appears to produce more serious symptoms in some people.

Dr Nicholson said people living or travelling throughout the Pilbara and Gascoyne regions should take extra precautions to avoid March fly bites, including:

  • wearing long, loose-fitting, light coloured clothing when outdoors
  • avoiding dark blue coloured clothing (there is some evidence that March flies are attracted to blue and other dark colours)
  • applying a personal repellent containing diethyl toluamide (DEET) or picaridin evenly to exposed skin (always follow the label instructions)
  • ensuring insect screens at home or on caravans are installed and in good condition
  • ensuring infants and children are adequately protected against biting insects, preferably with suitable clothing, including socks, and pram nets.

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