What are stable flies?

The stable fly (Stomoxys calcitrans), is also sometimes called the “biting fly” or “dog fly,” is a common fly which mainly bites horses and catlle , but also humans, dogs and pigs. Stable flies are difficult to distinguish from house flies, except that stable flies have a bayonetlike mouthpart (proboscis) protruding from the front of the head. See the picture opposite which shows the stable fly (top) and house/bush fly (bottom).

Adult stable flies (of both sexes) feed during the day, generally in the early morning and late afternoon. The female fly requires blood before she is able to lay eggs.

Click the image above to download the brochure "Fly Breeding Associated with Horticulture and Livestock". A joint publication by Agriculture WA, Entomology Section (Dr David Cook and Dr Ian Dadour) and the Health Department of WA, Environmental Health Service (Dave Peckitt and Owen Ashby).

The life cycle of a stable fly

Stable flies typically appear during midspring, they become severe during summer, and numbers tend to decrease in late summer. In prime breeding times stable flies can develop from egg to adult in just 2 weeks. Females lay over 100 eggs per batch and she may lay five batches in her lifetime, so there is the potential for rapid increases in fly numbers in a short period of time.

Where do stable flies breed?

The following information is kindly provided by Dr David Cook, a forensic entomologist from the University of Western Australia.  He has extensive experience with pests of humans and livestock and specialist knowledge on stable flies and many other nuisance fly species.

Stable fly larvae can develop in a range of animal manures, spilled feed and rotting organic material.  Pure manure rarely supports larval development, while rotting organic matter, either alone or in combination with various animal manures, is an ideal medium.  For example, poultry litter that has aged after exposure to soil and moisture is heavily exploited by stable flies.

Vegetative sources of stable fly breeding include rotting organic material, hay stacks/ bales, lawn clippings, vine litter, freshwater bay grasses, weeds and green chop silage.

Stable flies represent >90% of flies developing from rotting crop residues of either cauliflower, celery, broccoli, carrots, onions, potatoes and corn.  This residue comprises: i) stalks, leaves and fruit (either left in or on the ground after harvesting) and ii) harvested crop waste (i.e., damaged and rejected produce, processing scraps) dumped into open pits or fed out to livestock.  Other nuisance flies developing from rotting vegetable matter include the lesser house fly, false stable fly, blowflies, black carrion fly and flesh flies. 

Ways to reduce breeding numbers.

Stable fly development is reduced up to 95% when crop residues are treated prior to or immediately after incorporation into the soil with either diazinon or chlorpyrifos, which are commonly used insecticides in horticulture.  Crop residues left to rot in the field and untreated with pesticides can produce as many as 1,000 stable flies/m2.  If insecticides were applied several weeks after the crop residues were incorporated there was only an 11% reduction in stable flies.

Usage of poultry litter (poultry manure plus an organic sawdust base) as a fertiliser and soil conditioner in horticultural crop production is a contributor to both stable fly and house fly (Musca domestica L.) populations in south-western Australia.  From every hectare of broiler poultry litter (poultry manure plus an sawdust base) applied as a preplant fertilizer for vegetable production, an average of 1.5 million house flies and 0.2 million stable flies are produced (i.e. 150m2 and 20/m2 respectively). 

How can I stop stable flies breeding on my property?

The most effective for reducing stable fly numbers is to eliminate their breeding sources.

• Moist grass clippings should be spread thinly to dry.
• Maintain compost piles to promote rapid decomposition of organic matter, this generates heat and makes the pile unsuitable to fly larvae.
• Pest/Fly proof the outside of a structure eg: compost to prevent flies from entering. This technique includes caulking cracks, weatherstripping doors, and installing screens.

What should I do if I have stable flies?

Contact your local shire. Click here for more details on what to do.

Acknowledgements

Dr David Cook and Environmental Health Guide, EHS57, “Stable Fly”, Health Department of Western Australia. Click here to download the full brochure.