Stealth and beauty

Taking a closer look at the (slightly) misunderstood world of horseflies...

Okay, I know that horseflies aren't everyone's cup of tea. But just look at those eyes in the photo above. Aren't they beautiful. If I'm honest, horseflies aren't entirely my cup of tea either - when out and about with friends, I'm the one that horseflies and other bitey creatures are attracted to. One infamous day, I came home with 35 horsefly bites - I'd been swatting them away from me for hours and I itched for days afterwards. I don't really blame them, though, they were just doing what they needed to in order to ensure a bright future for their offspring.

I warn readers now - this is not a blog for the light-hearted. It is, however, a blog for those who want to know more about these beautiful, stealthy and trickier to love insects.

Large marsh horsefly on grass by Wendy Carter — Large marsh horsefly by Wendy Carter

Technically. horseflies don't bite. They have serrated mandibles that essentially saw into the skin until blood starts to flow; they then suck the blood. Unlike mosquitoes, they don't inject a mild anaesthetic, which is why their bites hurt more than those of other insects. This is probably because their more usual prey - cattle, horses and the like - have a much thicker hide than our human skin. It's only females that do this and it's only because they need protein for their eggs to develop. Surprisingly, perhaps, it takes six days to fully digest a blood meal so even if you spot a female, she may not be interested in you as a potential meal.

How do you know whether you're looking at a male or female? Pause for just enough time to see whether the eyes meet in the middle of the head - if they do (photo to the left), it's a male and if they don't (photo at the top of the page), it's a female.

Most horseflies are associated with watery habitats, the larvae usually living in muddy, damp soils or in the water itself. This is why you'll often find them around pools, marshy streams, woodland ponds and in damp meadows. The adults don't only hang around in these places, though, and a hot, calm sunny day they can appear almost anywhere in their hunt for a mate and food. I should point out that they also feed on nectar and pollen so they're not always just after a blood meal.

Kite-tailed robberfly (fly with large, hunched thorax and long body) eating notch-horned cleg (fly with brown body) — Kite-tailed robberfly eating notch-horned cleg by Wendy Carter

Don't worry. Just like everything in the natural world, horseflies have their part to play...and often get what we'd consider to be their comeuppance. Both adults and larvae are a really important part of the foodchain. Larvae are predatory but are also eaten by larger predators, such as wading birds. I once watched a wasp attack a horsefly, quickly and masterfully biting off its abdomen to take back to the nest to feed to the young. Adults are prey for birds, bats and even spiders as well as other flies - like this kite-tailed robberfly munching a notch-horned cleg. All of this as well as being great pollinators.

As far as I know, we've yet to work out why one person is more attractive to horsefly bites than another. I've read that eating garlic or bananas can help to deter them but I've no scientific proof to back up this theory. I was once told that allowing them to finish feeding would negate any reaction - one test later and I spent a day without itching...but it sadly didn't last into the next day. Covering bare skin with light-coloured loose clothing certainly helps as they're unable to get a purchase on your skin. There's a growing body of research that's looking into whether patterns (and zebra stripes) confuse and/or deter horseflies from settling and feeding. For some people, a bite means more than a small swelling and a bit itch - allergic reactions can occur and bites can become infected. If this happens to you, we'd recommend that you seek medical advice as soon as possible.

When you're next out and about and encounter a horsefly, perhaps you'll be brave enough to pause long enough to admire its beautiful eyes.