When the ice and snow have thawed and the sun makes its long-awaited reappearance, it’s time to pull out the shorts and tank tops and get ready for the first barbecue or picnic of the season. But your anticipation soon turns to dread as you remember what last year’s barbecue season was like: constantly battling the war against mosquitoes. Will this year be the same?
A lucky proportion of the population – around 15% – are naturally immune to mosquito bites. But for the rest of us, mosquitoes and the high likelihood of suffering multiple mosquito bites at an outdoor event can be enough to ruin the thought of the upcoming barbecue and picnic season.
This begs the question: why is it that some people are more likely to be bitten by mosquitoes than others? Luckily, we no longer need to wonder. Dr Jonathan Day from the University of Florida is a renowned entomologist and has been asking the same questions. As it turns out, a person’s likelihood of featuring heavily on a mosquito’s summer menu comes down to a unique combination of skin chemicals, body temperature, and natural body odours.
1. Natural Mosquito Repellents
By looking at the lucky 15% of people who seem to be naturally immune to mosquitoes and other biting insects, scientists have been hard at work trying to develop a mosquito repellent that actually works. Researchers at Rothamsted Research Lab in the UK have used chromatography to identify the chemicals produced by these naturally mosquito-repellent people to work out why mosquitoes steer clear. With this information, these researchers have been able to identify natural repellents that excrete just the right mixture of substances that mosquitoes can’t stand.
As it turns out, resistance to mosquitoes is highly hereditary. Many of the factors that determine how attractive a person is to mosquitoes are ones that are inherited from our ancestors, including blood type and metabolic rate. Since science has not progressed to the point of allowing people to modify their DNA, the genetic relationship between a person and the local mosquito population unfortunately cannot be changed.
Is it really true that pregnant women are more likely to be bitten by mosquitoes? As it turns out, this is more than an urban legend. Pregnancy causes a woman’s body temperature to increase by around 1.26 degrees Fahrenheit and to omit around 21% more CO2 than a woman who is not pregnant, making them around twice as likely to be bitten by mosquitoes. Luckily, this strange effect returns to normal following the end of the pregnancy.
4. Skin Bacteria
As strange as it is to think that we have various bacteria constantly living on our skin, it’s even stranger to realise that the types and levels of bacteria can change how attractive a person is to mosquitoes and other insects.
As it turns out, the fewer different species of bacteria on your skin, the more attractive you will be to mosquitoes. On the other hand, if you have a wide variety of different types of bacteria on your skin, mosquitoes are more likely to steer clear. This phenomenon explains why mosquitoes often target a person’s ankles and feet, as these areas of the body are more likely to host strong levels of only a few types of bacteria.
5. The Battle of the Sexes
It is a widely held belief that women are more likely to be bitten by mosquitoes because of their higher levels of oestrogen. However, this is largely untrue. In fact, the opposite holds to be true. Men are more likely to be attacked by mosquitoes simply because men, in general, are larger than women. The larger the person, the greater the levels of CO2 emitted, the greater the body temperature, and the greater the amount of lactic acid produced.
As much as you might enjoy a relaxing alcoholic drink on a balmy summer day, so too do mosquitoes enjoy the taste of alcohol. In fact, consuming three bottles of beer can line you up for around 30% more mosquito bites than if you hadn’t had anything to drink.
Mosquitoes’ preference for alcohol has little to do with the taste or feel of the drink, but everything to do with the way a person’s body temperature increases after they’ve consumed alcohol.
In fact, mosquitoes have been documented to eat fermented fruit, which is yet another indicator that there is something about alcohol that pleases them. To further complicate matters, mosquitoes are lucky enough – unlike humans – to have a naturally occurring enzyme to break down alcohol before it reaches their nervous system. This means that mosquitoes can happily consume alcohol, either through fermented fruit or through the blood of a human that has been drinking, without it having any typical alcohol-related effects on them.
7. Blood Type
Did you know that it’s actually only female mosquitoes that bite humans? Male mosquitoes are more interested in the nectar from plants and flowers, while females bite humans to access the protein in human blood, which they use to produce their eggs.
While scientists haven’t figured out exactly why, they do know that people with the O blood type are around twice as likely to be bitten by a mosquito than people with the A blood type, with B blood types coming somewhere in-between. As it turns out, the 15% of the population who are generally ignored by mosquitoes are people who – for reasons unknown – do not broadcast their blood type to the insect world. For this reason, mosquitoes don’t consider them to be a good source of blood and will leave them alone.
Mosquitoes are sensitive to colour, which is good news to humans as we can use this information to our advantage. It might sound counterintuitive, but wearing clothes in black and other dark shades can make you stand out more to mosquitoes than if you were wearing white or other light colours.
The reason comes down to a mosquito’s inability to fly in even a light breeze. To protect themselves from strong winds, mosquitoes have learned to compare the silhouettes of their prey against the horizon, enabling them to stay closer to the floor. Since the horizon is typically a light, bright colour, darker colours are more easily detected by a mosquito than light colours, which can blend in with the surroundings.
Similarly, a lot of movement can make it easier for mosquitoes to spot you as prey. The more you move around, the more likely it is that mosquitoes will recognise that you are easy prey and launch their attack.
9. Carbon Dioxide (CO2)
Think back to high school biology and you’ll remember that humans, as living vertebrates, are able to process oxygen and convert it into carbon dioxide. Mosquitoes have evolved to recognise carbon dioxide emissions as a way of distinguishing potential prey from other objects.
Of course, there is no way of completely eliminating carbon dioxide emissions, short of holding your breath indefinitely; however, there are ways of reducing the amount of CO2 you emit. People engaged in high levels of activity naturally emit greater levels of carbon dioxide due to their increased rate of breath. While this is something that you can control, your metabolic rate – the amount of energy your body uses in a set amount of time – is slightly harder to change. People with a higher metabolic rate emit greater levels of carbon dioxide than those with a relatively lower metabolic rate.
While your metabolism is largely part of who you are, it can vary somewhat due to your current circumstances. For example, exercising, consuming alcohol, or being pregnant or overweight can all have a negative effect on your metabolism and make you more attractive to mosquitoes and other biting insects.
When we sweat, we produce a mix of chemicals from our skin. Unfortunately, some of these chemicals – lactic acid in particular – are highly attractive to mosquitoes. While it is not possible to completely prevent your body from producing lactic acid, it is possible to minimise its production. Lactic acid is a type of metabolic waste produced as a result of the body’s ability to convert sugar into fuel.
Rather than inhibiting the production of lactic acid to ward off mosquitoes, it is more helpful to consider ways of reducing the amount of sweat your body produces. The easiest way to do this, of course, is to keep your body temperature at a reasonable level. Similarly, avoiding exercise while there are mosquitoes around will stabilise your body temperature and your body’s production of lactic acid, making you less likely to be bitten by mosquitoes and other biting insects.