Stop the bites! How to survive another summer of mosquitoes, midges and horseflies
It’s a good time to be a mosquito or other blood-sucking insect. In the UK and beyond, they are enjoying the summer heat, and there are lots of humans outdoors, some wearing very little, like an all-you-can-eat walking buffet. Some of the humans are drinking beer, which apparently makes them even more irresistible to mosquitoes. Many of us are warm and sweaty, which is all the better for the blood-suckers seeking us out.
Insect populations are changing because of the warming climate and there are organisations keeping an eye on invasive species, especially mosquitoes, which can be vectors for diseases such as dengue and malaria (globally, more than 600,000 people a year die from malaria). The UK “will have a threat from mosquito-borne diseases as time goes on,” says James Logan, professor of medical entomology at the London School of Hygiene and Tropical Medicine, and CEO of Dot, an “odour intelligence” company. “The biggest threats are arboviruses [viruses transmitted by arthropods, especially insects and ticks], such as dengue. We have mosquitoes throughout [mainland] Europe now that can transmit dengue. We also know that we do get those mosquitoes coming across to the UK, but they don’t seem to be breeding here successfully and surviving over the winter.” But, he warns, with milder winters and warmer summers, it is only a matter of time.
For now, mosquitoes – along with midges, ticks, horseflies and any number of blood-sucking insects – are a nuisance. Here’s how to survive the summer with them.
What is biting me?
It will probably be female. With most blood-sucking flying beasties, such as mosquitoes and midges, the males flit around, feeding on flower nectar for energy. The females, though, need a blood meal (we refer to it as a “bite”, but she essentially drills into you and sucks your blood). “Blood contains a lot of protein, and they use that to produce eggs,” says Logan.
How do they find me?
They are attracted to the carbon dioxide you breathe out, which they catch downwind. “It activates them and they begin to fly upwind,” says Jennifer Mordue, an entomologist and emeritus professor at the University of Aberdeen, of midgesand the other flying blood-sucking insects. “If they lose it, they begin to cast sideways until they hit it again. It’s a conditioned response to find those odours, and then as soon as they are a bit closer, they will be picking up other odours from the source.”
Don’t think you can outwit them by holding your breath – you also release some carbon dioxide through your skin.
Many blood-feeding flies, such as horseflies, are attracted to big shapes, movement and heat. “We’re quite large objects walking around the countryside,” says Erica McAlister, principal curator for diptera and siphonaptera (flies and fleas) at the Natural History Museum in London. “If you think of what they usually go for – large vertebrates – they are attracted to dark large objects.”
Contrasting colour can also catch their attention. A white T-shirt against a pair of black shorts, for example, may pique their interest. “Light-coloured clothing is probably the better option,” says Logan. And, he adds, it means you are more likely to spot a mosquito landing on you.
Ticks – which are not insects, but arachnids, like spiders and scorpions – are also attracted to carbon dioxide, sweat and body smells, as well as heat and movement, but seem to be largely opportunistic, waiting for a human or other animal to come close enough for them to hop on.
Why do I always get bitten?
Much of the research about this has been focused on mosquitoes, and it is mainly to do with the way you smell. “We all smell differently, and mosquitoes can pick up on that,” says Logan. “That tends to be what drives their behaviour,” he says, and it is what makes one person more attractive than another. Our smell can be affected by hygiene and diet, but a lot of it is genetic. “We know that identical twins will be bitten about the same amount as each other, but non-identical twins will be bitten different amounts,” says Logan.
It has been suggested that blood type can make a difference. “Some papers have shown that there may be something to do with blood type, or that mosquitoes can breed better when they feed on certain blood types,” says Logan. “But the evidence is scarce.”
Mordue studied midges and who they are attracted to. They are also lured by smell. “About 300 different chemicals come off our skin all the time, our own individual components. We discovered that there are a few compounds that are attractive to them, and some that are not.”
There is evidence to suggest that larger, taller people (therefore, usually, men) tend to be more of a target. “But, of course, you do get smaller people where the odour is more important,” says Logan. “Odour certainly is the strongest driver.”
Can I change the way I smell?
Not really, says Mordue. “It has nothing to do with eating garlic or these things that you hear. There may be some evidence that your smell changes with menopause, but I don’t think that is very strong. So, really, you are what you are in terms of these compounds.” Logan has heard the myths – taking brewer’s yeast tablets, eating Marmite, drinking gin and tonic – but says: “None of that stuff works well.” There is some evidence that drinking beer can make you more attractive to mosquitoes. Logan says this may be to do with beer altering your smell – the compounds on your breath or skin – but, he adds: “It could just be that when you’re drinking alcohol, your body temperature tends to go up a bit. That might make you sweat more.”
In terms of smell, insect repellant is the only thing that will help, he says. Dousing yourself in perfume won’t mask your underlying scent. “Mosquitoes have evolved for millions of years to be really sure that we are human, and so they know what our smell is.” Insect repellants contain compounds that do affect our attractiveness, but perfume, however strong, is “nothing that a mosquito can’t see through”.
Do wash more, though, Logan adds. “Mosquitoes really like stale sweat, so if you haven’t washed your feet or had a shower, you’re likely to be more attractive to mosquitoes.”
Why does it hurt?
It depends on what has nibbled you. You probably won’t feel a mosquito feeding on you, says Logan. It sinks its needle-like mouthpart into your skin, which it can bend and move around “until it finds a blood vessel, then it sucks the blood. At the same time, it’s injecting saliva into the bloodstream, and that stops the blood from clotting. It’s like an anticoagulant, but also contains an anaesthetic, which means you don’t really feel it when it’s happening.” It’s the saliva, “a foreign substance”, that your body reacts to.
A horsefly bite hurts, says McAlister, because they are more brutal. “They slice your flesh and then lap up the pooling blood. It’s a physical ripping of your skin.” Horseflies are mostly found in the countryside, and – the clue is in the name – humans are not their preferred meal, so they are less sneaky. “These are used to large vertebrates that don’t have mobile limbs in the same way,” says McAlister. “Hence they seem clumsier and they risk more death – we were never their intended target to start with.” Stable flies, which look like houseflies and are usually found around agricultural areas, have “a proper stabbing proboscis”.
How can I avoid being bitten?
Depending on the species, some mosquitoes are commonly active at dawn and dusk, says Logan, “and some will feed throughout the night. But there are species of mosquitoes that feed throughout the day as well.”
Wear long, loose clothing. “If you’re wearing tight jeans, a mosquito will happily bite through them, even though it’s very thick material,” says Logan. “What you want is baggy clothing, which decreases the likelihood they are going to land on a bit of fabric that’s touching the skin. Keep your windows and doors closed. If you have a garden, make sure there’s nothing that’s collecting water there – some mosquitoes will breed in an upturned bottle lid, a very small amount of water.”
Insect repellant works: those containing Deet, picaridin, IR3535 and oil of lemon eucalyptus (or OLE), are all recommended by Logan. But, he says, citronella, which is often used in candles supposedly to repel insects, “doesn’t work particularly well, and it’s therefore not recommended”.
Check the weather forecast to do your best to avoid midges. “They can’t fly in winds that are more than about 4 or 5mph,” says Mordue. “They don’t fly if it’s below 13C, so even in the summer, you’d be fine on a cool day.” They do like low-level cloud and humidity. “They have this diurnal rhythm of flying at dawn and dusk, so perhaps don’t sit outside and have your gin and tonic in the early evening.”
When McAlister does field work, long sleeves and trousers provide a barrier against ticks. “We check each other afterwards,” she says. Some horseflies, she says, “apparently attack at different heights depending on the species”. One type, chrysops, tend to come from behind the head, “whereas the haematopota, which has the amazing dotted wings, go for wrists. Go out with a big floppy hat and wrist cuffs, looking like a dandy from the 1800s.”
You may want to consider clothing with a print. There is “an amazing, very amusing study, in which they dressed horses in stripes, as zebras”. The researchers found horseflies landed less often on horses wearing a zebra-striped coat, suggesting the pattern confused the flies. You can try your own version of disruptive colouring – some jaunty stripes, perhaps. “It’s harder for them to figure out where you are,” says McAlister. She recommends “light colours, disruptive colours, loose clothing – and hanging around with someone who is bitten more than you”.
How should I treat bites?
Try not to scratch a bite, says Logan. “It’s really hard because most people will have an itchy lump. But if you scratch it, you open it up into a larger wound and that can cause an infection. When there are mosquitoes around, it is likely to be quite hot. You tend to be sweaty, you may be outside, there are bacteria around, and there’s a chance that the wound will become infected.” If you tend to react badly to bites, you can take pre-emptive action with oral antihistamines, which your GP can prescribe. You can also buy over-the-counter antihistamine cream. “You need to put it on the bite pretty much immediately because that is when the histamine that causes the itch is produced,” says Logan. Then keep the bite clean while it heals. “If it does become infected, it’s important to seek medical help because you may need antibiotics,” he says.
If you find a tick on your skin, says McAlister: “Most of the time, you can remove the tick and have no problems. But if you do see a telltale circle [often referred to as a bullseye pattern] that surrounds the bite, seek medical help.” The same goes for flu-like symptoms such as fatigue, headache, fever and aches.
Can we change our attitude to blood-feeders?
“You have to learn to live with midges,” says Mordue – and try not to let them put you off a holiday in Scotland. McAlister says all the insects are “important pollinators. I know it’s a nuisance, but they are quite important components of the ecosystem.” Think of the number of eggs and larvae going into the environment. She says it’s important to consider the bigger picture. “What do you think all the birds are feeding on? A huge part of our aerial plankton is suddenly this mass emergence of midges and mosquitoes. So we’ve got to be careful when we start saying we want to eradicate things.”
Reporting from The Guardian contributed to this story.
