Mosquitoes and black flies


Mosquito numbers can increase after floods, storms and cyclones as standing water from heavy rainfalls and flooding are ideal conditions for mosquito breeding. Higher numbers of mosquitoes lead to a higher risk of being bitten and contracting mosquito-borne diseases.

Symptoms of mosquito-borne diseases vary but 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.

In rare cases, infection may cause brain inflammation (encephalitis). Seek prompt medical assistance if you experience any of these symptoms.

Learn more about mosquito-borne diseases found in Queensland.

Protecting you and your family

Your best defence against mosquito-borne diseases is to avoid being bitten. Different mosquitoes prefer to bite at different times of the day and night. It's important to avoid being bitten. Always use personal protection methods and remove potential breeding sites around your home.

Avoid being bitten

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

  • Avoid mosquitoes when they are most active, particularly at dusk and dawn. Some mosquitoes, including those that transmit dengue, bite during the day.
  • Apply insect repellent on exposed skin and reapply every few hours (follow the instructions on the repellent), especially when outside at dawn or dusk.
  • Wear long, loose, light-coloured clothing and closed-in footwear.
  • Use flying insect spray, mosquito coils (outside) or plug-in insecticide devices to kill mosquitoes indoors.
  • Check that the flyscreens in your home are in good condition so mosquitoes can't get in.
  • Use mosquito nets when sleeping if your windows or doors don't have flyscreens.


The Australian Pesticides and Veterinary Medicines Authority (APVMA) has approved and recommends the use of personal repellents that contain DEET (Diethyl Toluamide), picaridin or oil of lemon eucalyptus (also known as PMD; p-methane-3,8 diol).

Products approved by the APVMA have been assessed as safe and effective when used following the directions provided on the label. Avoid using unregistered repellents and those sold from unknown, overseas suppliers, as their effectiveness and safety may be unknown.

You can search to make sure your repellent is registered with APVMA using the Public Chemical Registration Information System Search.

Repellents and children

Repellents containing less than 10% DEET or picaridin are considered safe for children.

Topical repellents are not recommended for infants under 3 months of age. Instead, use physical barriers such as nets on prams and cots.

Young children should not apply repellent on themselves, they need to be applied by a parent or carer.

Clearing your home

You should remove potential mosquito breeding sites from around your home regularly. After flooding or heavy rain, you should also:

  • Clean up around your house and yard following a cyclone or flood once it's safe to do so.
  • Wherever possible, remove any pools of standing water, including clearing debris from ditches, cutting small channels to drain pooling water, or filling in holes or vehicle treads.
  • Clean up debris deposited on your property by flood waters or cyclones. Debris and rubbish often pool 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 water out of containers, store them in a dry place or dispose of them responsibly. Containers that commonly become mosquito breeding sites include:

  • pot plant bases (inside and out)
  • tyres
  • tarpaulins and plastic sheeting
  • plants, e.g. bromeliads, palm fronds, coconut shells
  • buckets
  • tin cans and plastic containers
  • boats
  • roof gutters, especially if blocked by debris
  • any rubbish that may hold water.

Rainwater tanks can also be a potential breeding site:

  • check the mosquito screens and flap valves on rainwater tanks to ensure they are in place
  • make any necessary repairs.

Read other steps you can take to control mosquitoes around your home.

Black flies

Black flies (Austrosimulium) can also increase after a flood or heavy rain, particularly in inland areas. While black flies don't transmit disease, their bites may cause allergic reactions and bacterial skin infections can occur from bites and scratching the bite sites.

Black flies are aggressive biters and are found in locations around streams and rivers. They breed in running water, and once flood water recedes, black fly numbers rapidly decrease.

They are only active during the day; their peak activity typically occurs from sunrise to mid-morning (10am) and late in the afternoon (4pm) to sunset. They don't bite at night.

Female black flies are blood feeders. Their bites can itch and cause discomfort for several days. Anticoagulants, blood thinners that stop the blood from clotting, injected by black flies into the bite site can cause allergic reactions.

Signs, symptoms and treatment

Signs and symptoms associated with black fly bites can include:

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

You should manage black fly bites to prevent secondary skin infections. You can do this by:

  • applying calamine lotion or another anti-pruritic preparation to bite areas to stop itching
  • cleaning inflamed bites with soap and water at least once a day, applying antiseptic lotion and keeping the bite covered with a dry dressing
  • keeping affected limbs elevated
  • washing your hands before and after touching open wounds
  • monitoring skin sores—if they become hot, red, swollen and painful, seek medical attention as soon as possible.

Preventing black fly bites

Protecting yourself and your home after a flood or heavy rain is the best way to avoid black fly bites:

  • apply an effective insect repellent on exposed skin, following manufacturer's instructions
  • where possible, avoid outdoor activity during the morning and afternoon
  • wear light-coloured, loose-fitting clothing when contact with black flies is likely
  • keep shirt and sleeves closely fastened (shirts with zippered fronts keep flies out better than buttoned shirts), and tuck trousers inside socks or high boots
  • make sure fly screens on doors and windows are intact
  • if needed, use a knock-down insect spray following manufacturer's instructions.

Further information