March flies (also commonly known as deerflies or horseflies) are a diverse group of large blood sucking flies that cause painful bites, severe irritation and blood loss (Figure 1 and Figure 2). Heavy attacks can lead to significant production losses such as reduced weight gain.
Figure 1: Tabanid March fly. Image courtesy of Jess Morgan, Queensland Department of Agriculture and Fisheries
March flies are vectors of important livestock production diseases exotic to Australia such as surra. Control of March flies could become extremely important if some of these exotic diseases were to enter Australia.
March flies are often large agile flies. Only the females bite animals including humans to obtain a blood meal for producing eggs.
Figure 2: Close up of a March fly, Tabanus latipes, showing the solid, piercing mouthparts used for feeding on blood. Image courtesy of Mukund Madhav
March flies occur throughout Australia. There are over two hundred species, with each adapted to fulfil a different ecological niche. This means that March flies are usually present all year round in most locations but have strong seasonal spikes in abundance such as during the wet season in northern Australia.
March fly bites are painful and can lead to behaviours of extreme annoyance, dermal nodules, secondary myiasis from other flies, anaemia and loss of weight and milk production.
Regular checking of stock will detect signs of irritation from March flies, such as defensive reactions, interruption of grazing, bunching up and seeking shelter. Fly traps can be used for surveillance of fly activity, but trap catches do not indicate the severity of attack on livestock.
Most farmers are more concerned about other flies such as buffalo flies and other ectoparasites such as ticks and lice and design control strategies around them. Because March flies generally have short feeding durations compared with these other pests, pesticide levels typically used may have limited effect against them.
As March flies are not livestock dependent, they are difficult to control. Fortunately, they appear to prefer to feed on native wildlife and do not generally cause severe problems in cattle in Australia. March flies prefer woodland and therefore exposure of livestock can be reduced by grazing animals in open pastures at times of peak March fly activity.