There are about 400 species of March fly in Australia. Some of these feed on flower nectar and pollen but the majority prefer a helping of blood.

Anyone who’s come into contact with a March fly, also known as a horse fly, is not likely to be very welcoming to the next one they come across.

March flies, common across southern Australia during summer, are known for their short, sharp and stinging bite. Many a time have we felt the shock of a bite on your leg and then been surprised when you look down to find the culprit is a fly—and still sitting there by the way.

Just when you thought the incessant buzzing of the flies in summer was bad enough, now they’re biting us as well.

Black fly with large green eyes

The March fly’s bite can deliver quite a sting. dracophylla/Flickr

Dr David Yeates, the director of our Australian National Insect Collection and an expert on flies (Diptera), says that the March flies are after our blood. Just like a mosquito, the female March fly bites us to get at our blood. It then uses the protein in the blood to develop eggs, which give rise to the next generation of March flies.

So that explains why they are so insistent.

Dr Yeates says that the painful and itchy reaction that can follow a bite is caused by the anticoagulants the fly injects us with when feeding on our blood. The anticoagulants are chemicals in the fly’s saliva that prevent our blood from clotting and ensure a steady flow for them to feed on—again, this is similar to a mosquito.

There are about 400 species of March fly in Australia. Some of these feed on flower nectar and pollen but the majority prefer a helping of blood.

March flies are not too picky about where the blood comes from either; if you’re warm blooded then you’re a target. Horses come in for quite a bit of attention, hence why the flies are also known as horse flies. Dr Yeates says that in North Queensland the flies have even been seen feeding on Crocodiles!

Dr Yeates was recently interviewed by the ABC about March flies, read the interview.


  1. Have huge swollen bites on my leg and back and feverish and sick. I hate how I react to thesr bites. They thought the rwpellant was tasty.

  2. Camping in the Bundaberg Region next to the Isis River last week, we had the worst attack of Marchies I’ve ever experienced. I had aerogard on but made the mistake of walking around in shorts and a singlet at late dusk. I didn’t even see or feel them at the time, but woke up in the morning with about 80 to 90 bites all over my legs, arms and shoulders, itching like crazy. The flies I saw were a light green colour but otherwise identical to the brown ones that have harassed me in Victoria and NSW. I thought putting repellent on would work…but alas, no. Any opinion from the CSIRO on what works?

  3. Pilbara match flies are bad! Last year my mate had an anaphylactic reaction and had to be taken by RFDS to Hedland Emergency.
    This week he got another bite and then got hives all over his body.
    I got about 30 bites while running outdoors after work. Should’ve put insect repellent on! They have remained incredibly itchy 4 days later!

  4. Feb 2021 and they are out on Macrae beach, Mornington Peninsula. I have over 16 bites, of which a few have become larger red lumps. The itching sensation is incredible and has persisted for over 24hrs even with oral antihistamine and topical hydrocortisone cream. I didn’t even know they could do this to a person. I’m miserable.

  5. They are a nuisance for sure. I live on the south coast of WA where I encounter a large sized fly. At least I often feel it land and can swat it before it gets its proboscis into me. Currently though, I’m working in the Pilbara and the ones that are biting me here are smaller in size, they but man, they have a bigger bite! To add to that, they itch days afterwards. Most annoying.

    1. In Walpole area of WA I was told that they emerge when the Yellow Tingle flowers (a white flower) and the flies are drunk on the pollen. We have had success wearing hi-vis yellow shirts (long sleeves, collar up). They seem to NOT like this bright colour. I’ve found Aerogard and RID the best for me, and use old-fashioned Calamine lotion on the bites.

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