Mosquitoes and black flies


Mosquito numbers can increase after floods, storms and cyclones as standing water from heavy rainfall and flooding provides optimal conditions for mosquito breeding. Increased numbers of mosquitoes lead to an increased risk of being bitten and mosquito-borne diseases.

The most common mosquito-borne diseases in Queensland are caused by Ross River and Barmah Forest viruses. Outbreaks of dengue have been reported annually in north and central Queensland. Zika virus, Murray Valley encephalitis (MVE) virus, and a strain of West Nile virus called Kunjin virus have also rarely been reported.


The incubation period for mosquito-borne diseases varies. Symptoms are usually present 3–15 days after being bitten by an infected mosquito. Common signs and symptoms are:

  • headache
  • fever
  • joint or muscle pain
  • skin rash
  • fatigue
  • nausea.

Most people infected with Kunjin virus, Zika virus and MVE viruses do not develop symptoms. However, those with symptoms typically experience:

  • fever
  • muscle pains
  • headaches
  • tiredness
  • joint pain/swelling.

In rare cases, infection may result in brain inflammation (encephalitis). It is important to seek prompt medical assistance if symptoms are experienced.


Mosquito-borne viruses are transmitted via bites by infective mosquitoes and cannot be transmitted directly from person-to-person. Different mosquitoes prefer to bite at different times of the day and night. It is important to be vigilant at all times and use the personal protection measures listed to prevent being bitten.


If diagnosed with a mosquito-borne disease it is important to prevent being bitten again by mosquitoes to ensure the disease transmission cycle does not continue. Contact your doctor or healthcare professional for advice on the most appropriate course of action.


The best way to prevent mosquito-borne diseases is to prevent mosquitoes from breeding. You can reduce the number of potential breeding sites around your home by:

  • cleaning up around your house and yard following a cyclone or flood
  • removing any pools of standing water around your house and yard—this may involve clearing debris from ditches, cutting small channels to help pooling water drain, or filling in holes and vehicle wheel ruts
  • cleaning up debris deposited on your property by flood waters or cyclone. While a lot of this debris may be half-buried, it often contains enough water to produce large numbers of mosquitoes.

Rain or floodwater may have also collected in containers around your yard, so make sure you tip the water out of the containers and store them in a dry place or dispose of them responsibly. Common mosquito breeding sites include:

  • pot plant bases (inside and outside)
  • tyres
  • tarpaulins
  • plants e.g. bromeliads, palm fronds, coconut shells
  • buckets
  • tin cans and plastic containers
  • boats
  • roof gutters (if blocked by leaf debris).

Rainwater tanks can also be a potential breeding site for mosquitoes. You can reduce risk by

  • checking the mosquito screens and flap valves on rainwater tanks—particularly in-ground tanks— to ensure that the screens and flap valves are still in place
  • making any necessary repairs.

Avoid being bitten

There are several simple steps you can take to reduce your risk of being bitten by mosquitoes including:

  • applying insect repellent (in accordance with manufacturer’s instructions), especially when outside at dawn or dusk. Personal repellents containing DEET or picaridin are more effective than other repellents. Repellents containing less than 10% DEET or picaridin are considered safe for children, however the use of topical repellents is not recommended for infants under 3 months of age. It is best to use physical barriers—such as nets on prams and cots—to protect infants less than 3 months of age. Young children should not apply repellents themselves. Repellents should be applied to the hands of a carer first, and then applied evenly to the child’s exposed skin.
  • protecting against mosquito bites during the day in dengue receptive areas (North and Central Queensland) as dengue mosquitoes bite during the day and like to rest indoors
  • wearing long, loose, light-coloured clothing
  • using flying insect spray or plug-in insecticide devices to kill mosquitoes indoors
  • using bed nets, if available
  • repairing defective insect screens.

See a doctor immediately if you become unwell with fever, headache, skin rash, joint or muscle pain.

Black flies

The number of black flies (genus Austrosimulium) can increase following a flood or heavy rain, particularly in inland areas. While black flies do not transmit disease, allergic reactions and bacterial skin infections may occur from bites and scratching the bites.

Black flies are aggressive biters that are found in areas around streams and rivers. They breed in running water—but once flood water recedes the number of black flies rapidly decrease. Black flies are active only during the day and do not bite at night. Their peak activity period tends to occur from sunrise to mid-morning (10 am) and late afternoon (4 pm) to sunset.

Female black flies are blood feeders—their bites can itch and persist for several days. Anticoagulants—a blood thinner that stops the blood from clotting—injected into the bite site by black flies can cause allergic reactions in sensitive individuals.

Signs and symptoms

The range of signs and symptoms associated with bites can include:

  • painful, itchy bite lesions
  • urticaria (itchy raised skin rash)
  • cellulitis (hot, red, swollen and painful skin and underlying tissue infection).


Black fly bites should be managed to prevent secondary skin infections by:

  • applying calamine lotion or another anti-pruritic preparation to bite areas to prevent itching
  • cleaning inflamed bites with soap and water at least once daily, applying an antiseptic lotion and keeping the bite covered with a dry dressing
  • keeping affected limbs elevated
  • washing hands before and after touching open wounds
  • observing skin sores. If skin sores become hot, red, swollen and painful, seek medical attention immediately.


Black fly bites can be avoided by:

  • applying insect repellent in accordance with manufacturers recommendations.
  • using physical barriers, such as nets on prams and cots, to protect infants less than three months of age
  • where possible, avoiding outdoor activity during the morning and afternoon
  • wearing light coloured loose fitting clothing when contact with black flies is likely
  • keeping shirt sleeves and your shirt front closely fastened (shirts with zippered fronts keep flies out better than buttoned shirts), and tucking trousers inside socks or high boots
  • ensuring insect screens on doors and windows are intact
  • using a knock-down insect spray in living areas.

Personal repellents containing DEET or picaridin tend to last longer than other repellents depending on the concentration. Repellents containing less than 10% DEET or picaridin are considered safe for children, however the use of topical repellents is not recommended for infants under 3 months of age. Young children should not apply repellents themselves. Repellents should be applied to the hands of a carer first, and then applied evenly to the child’s exposed skin.

Further information