Biting Midge (sand flies)

Distribution

Biting midges occur in many coastal and inland areas of Western Australia (WA). They are most commonly found in tropical and sub-tropical parts of the state near sandy estuarine and foreshore areas and mangrove swamps. They are very common in some coastal areas of north-west WA.

Many species will only travel a few hundred metres from their breeding sites, while others may travel several kilometres.

Activity

Biting midges are most active under calm conditions. They are most prevalent around dawn and dusk, but may continue to bite through the night and during overcast days.

Breeding

Biting midge commonly breed around the edge of water bodies, with the adult female laying her eggs in places like damp soil, moist decaying leaf material and muddy, sandy or vegetated substrates.

The biting midge lifecycle includes a worm-like (larval) and cocoon-like (pupal) stage before the adult emerges. This can take between 3 and 22 weeks, depending on the environmental conditions and the type (species) of biting midge.

Emergence of adult biting midge is associated with the new and full moon phases, especially for midge species breeding in (intertidal) coastal areas. The adults can live for several days to months depending on the species.

Feeding

As with most biting flies (including mosquitoes), only the females bite, using the blood they obtain as a protein source to develop their eggs. The males feed on plant nectar only.

Biting midges are not known to transmit any human diseases in Australia, however, bites often cause a severe local (allergic) reaction and can be painful and/or irritating for some people.

The severity of the reaction varies from person to person. People who are regularly exposed to biting midges may become desensitised over time, eventually experiencing only a very mild reaction or no reaction at all. Others, including tourists, may experience a severe reaction with red, swollen bites measuring several centimetres in diameter. Some people may not be aware that they have been bitten as the itching may not commence for several hours after the bites.

The bites are usually painful and itchy. They may also form blisters, become weepy and persist for days or weeks. Scratching the bites can result in a secondary bacterial infection.

Treatment

Symptomatic treatment, including application of an ice pack and use of an antihistamine, may offer relief from painful bites. Secondary bacterial infection may require the application of antiseptic cream or the use of antibiotics.

In severe cases medical advice may be required.

The simplest way to prevent being bitten by biting midges is to cover up with appropriate clothing and/or apply an effective repellent product.

The following information may assist in reducing bites:

Cover up and use repellents

• Avoid being outside around dawn and dusk and at other times if biting midges are active. 
• Cover up with long, loose-fitting and preferably light-coloured clothing. 
• When outdoors, carry an effective insect repellent, containing either diethyl toluamide (DEET) or picaridin, for use if biting midges are active. 
• Repellent reapplication may be required after swimming, as the product may wash off.
• Natural or organic repellents are generally not as effective as DEET or picaridin and may need to be applied more frequently.
• The best protection for babies and young children is to dress them in protective clothing, socks and shoes, use fine mesh bed nets and other forms of insect screening. 
• Repellent application is not recommended in children under the age of 12 months of age. Repellents containing up to 10% DEET or picaridin can be used on children from 12 months. 
• Correct application of insect repellent (Healthy WA) is critical in ensuring the product remains effective.

Houses

• Ceiling fans or other air circulation devices may discourage midges from biting.
• Screen all doors and windows with a fine mesh. Biting midges are very small and can fit through standard fly screens.

Travelling and camping

• When planning holidays or outdoor activities choose locations well away from midge breeding sites/wetlands. 
• Be aware of the phases of the moon. Adult biting midges often emerge during new and full moon phases.
• Screen caravans, tents and other camping gear with a fine mesh. 
• Increase the effectiveness of insect screens and other biting midge ’resting areas’ by using residual surface spray insecticides. 

Biting midges are one of the most difficult groups of insects to control as no chemicals are currently registered in Australia to control them in their breeding sites. The sheer size of their breeding sites also makes chemical control unrealistic.

Adult midges can be temporarily reduced using insecticides (fogging) but once the chemical droplets have settled, midges can re-infest treated areas. Fogging must be undertaken with caution and in strict accordance with label directions as it is not target specific.

Residual chemical sprays can be applied to places where biting midges may rest such as the walls of a building, shade-cloth awnings, insect screens and vegetation to help reduce adult numbers. Some residual spray products can control biting midges for up to six weeks, depending on environmental conditions.

It is important to remember that repeated use of residual sprays can have a negative impact on other insect and spider populations. Always read the label and apply residual sprays in accordance with the manufacturer’s instructions. It may be appropriate to enlist the services of a registered pest management technician.