Description and life cycle
The adult stable fly is slightly smaller than a house fly and slightly larger than a bushfly but has a checkerboard of dark spots on the back of the abdomen.
Stable flies have a prominent black proboscis that is used to pierce the skin and draw blood.
The life cycle from egg to adult is about 13–18 days in temperatures ranging from 24 to 30°C. At lower temperatures (10–20°C), such as those likely to be experienced over winter, development can take three to five months.
After ingesting a blood meal, the female fly lays around 90 eggs in four or five suitable locations such as rotting vegetable matter or animal manure. She may lay up to 600 eggs over a lifetime and in warmer areas may breed all year-round.
In summer the eggs hatch in as little as 20 hours and the active larval stages, which are extremely heat-tolerant, begin feeding for up to a week before pupating. The red-brown to black pupae are the size of a grain of rice, and can take as little as five days to emerge at high temperatures or up to 30 days at lower temperatures.
After emergence, the adult flies disperse, sometimes covering tens of kilometres in search of a host animal. Both male and female adult flies feed on blood, as soon as six hours after emergence.
The adult flies live for about three to four weeks, with extreme heat (over 35°C) reducing their lifespan to just two weeks.
The flies mostly feed in the morning and again in the late afternoon when they can extract five times as much blood as a mosquito with each meal.
The fly will make several attempts to feed, adding to the distress of its host. Once settled on an animal, it takes 2–5 minutes to complete the blood meal, after which it seeks a shady place to digest it.
This adaptable fly will breed in any rotting or decaying organic matter where there is a high degree of bacterial activity. Key breeding sites include:
- ageing manure mixed with organic material such as straw
- rotting vegetable crop residues left after harvest, including reject produce
- straw bedding mixed with urine and faeces
- reject vegetables fed out to livestock in large piles
- rotting hay, straw or sawdust, fermenting feed and piles of grass clippings.
Stable fly control
The key to stable fly control is managing its larval habitats, ideally by their removal or drying out so they are less attractive.
Treating livestock or pets with insecticides and repellents can aid in control, however the impact is often short-lived (hours to days).
If treating livestock with insecticide, application to the lower legs and underbelly of the animals is critical. Using commercial or home-made fly traps can help to reduce fly numbers in local situations.
Eliminating breeding sites
There are a number of management practices that will remove breeding sites:
- Mulching and burying vegetable crop residues and reject produce soon after harvest, and then compacting the soil above the residues using a land roller.
- If feeding waste vegetables to livestock, do so in long thin lines or in a trough or box to prevent mixing with the soil.
- Regular removal of accumulations of spilled grain feed or other organic material in pens and yards.
- Regular (weekly) removal of animal manure and soiled straw accumulating in pens and yards, around water troughs and under fences and gates.
- Animal manures should only be stockpiled for a short period (less than three days) before covering with plastic to protect them from getting wet.
- Covering animal feed and bedding waste with a fly-proof barrier and keep it completely dry with a tarp or plastic sheet.
- Spreading animal manure and grass clippings into thin layers on the ground to dry out.
- Manure can also be used as a blend for compost or sprayed with insecticide to prevent fly development.
The previously recommended method of slashing the residue, leaving it on the surface, spraying with pesticide and turning water off has been phased out, as compaction is a far more effective method of reducing stable fly development.
Stable fly specific traps
Protein-based traps put out to catch houseflies, blowflies and bushflies will not catch stable flies because they are not attracted to rotting protein.
White boards with a sticky surface will attract them as they are likely to rest on a cool, vertical surface after a blood meal.
The Williams trap is the simplest form and uses a white alsynite panel painted with a non-drying glue such as Stikem® to catch the flies. These traps are specific to stable flies and catch very little else.
To make your own trap, heat the non-drying glue on a hot plate or over hot water so that it thins out and can be used more easily. Cover both sides of the alsynite board with the glue. Secure the white board to a star picket about 1m from the ground to avoid it becoming covered in dirt and dust.
One litre will suffice for up to 15 traps. When the white board is covered with flies, remove the glue with a paint scraper before re-applying.
Visit your local hardware store to enquire about alsynite panels and non-drying glues.
Insecticides and repellents can be used to keep stable flies away from livestock, animal yards and places where the fly rests. Numerous products on the market range from residual sprays to animal backline pour-ons and sprays, to insecticide-impregnated ear tags.
The relative effectiveness of these products has not been tested but it is thought the flies quickly overcome any initial repellent action. The best option may be to use three or four different repellent sprays, in regular rotation.
Residual sprays should be applied where the flies rest (e.g. shady surfaces, fences, walls) so the insecticide residue can be absorbed, thus killing them. These are effective for about one or two weeks, but rain, high temperatures and sunlight all reduce the residual effect.
Check for current information on stable fly products on the APVMA website.
Stable Fly Management Plan
The Biosecurity and Agriculture Management (Stable Fly) Management Plan 2019 was published in the Western Australian Government Gazette No. 127 (3 September 2019). This updated plan replaces the Stable Fly Management Plan 2016, and outlines the measures to be taken to control stable fly in areas where it is a declared pest.
The Stable Fly Management Plan 2019 includes the control measures from the previous plan as approved measures for a period of two years. This will allow for the transitioning from the old plan to the updated plan measures. Please note, this transition phase ends on 03 September 2021. After this date the control measures from the previous plan will no longer be approved measures.
Periodically the Stable Fly Management Plan 2019 may be modified to allow new measures and/or control methods to be adopted. To maintain the integrity of the Stable Fly Management Plan 2019, only new measures and/or control methods that can be proven to result in similar control rates will be adopted.
LGA officers who wish to become authorised under the BAM Act to undertake compliance activities for stable fly should email: firstname.lastname@example.org for information.
Dr David Cook, Senior Entomologist, UWA, is thanked for providing technical information for this web page.