Biologists Think They Know How Mosquitoes First Got Their Thirst For Human Blood

It’s a warm summer’s evening, and you’re relaxing in your garden after a long day. That tranquility is soon disrupted, though, when you realize you’ve been bitten by a mosquito. Maybe you felt it pierce the skin and swatted it away; more likely, you never noticed it at all, and now your bite is starting to itch. Prior to that, you might not have thought about why these pesky insects crave human blood, but a research paper finally answered the question in July 2020.

Due to the hot conditions, mosquitoes are particularly bothersome during the summer months, buzzing around yards across the country. As reported by the Mosquito Reviews website, the heat cuts down their life expectancy, which causes them to produce extra offspring. And on top of that, a greater number of eggs start to crack open too.

In total, the Inverse website claimed that you can find roughly 3,500 different types of mosquito across the globe. To break things down even further, the American Mosquito Control Association also stated that 176 of those are situated in the U.S. But if you’re bitten by the bug, the sting could be the least of your concerns.

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Indeed, certain mosquitoes are known to harbor dangerous diseases that subsequently get passed on when they bite people.Incredibly, the World Health Organization (WHO) reported that millions of individuals lose their lives to these ailments annually. Malaria is one of the biggest killers, with the agency unveiling another shocking figure via its website.

Back in 2015 some 438,000 people died from malaria alone, with the WHO noting that Anopheles mosquitoes were capable of spreading the disease. Meanwhile, the Aedes aegypti species carries a range of different illnesses as well. For instance, they can pass on dengue fever, the Zika virus, yellow fever and chikungunya.

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To explain more, a doctor named Amesh Adalja sat down to talk with Time magazine in January 2016. He worked for the Center for Health Security at the the University of Pittsburgh Medical Center, focusing on infectious ailments. During his chat with the publication, Dr. Adalja detailed what happens when mosquitoes feed on humans.

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Dr. Adalja said, “Mosquitoes literally drink blood, and by doing so ingest microbes directly and can pass them directly into the bloodstream of others. They are very mobile and can move over distances [of] a few miles. [That allows] them to have some trajectory in finding their blood meals and spreading disease in the process.”

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But another individual made an equally troubling point while speaking with Time. Janet McAllister plied her trade at the U.S. Centers for Disease Control and Prevention (CDC) as an insect expert, and she touched upon the mosquitoes’ feeding habits. In her opinion, the timing of the sting could determine whether you get sick or not.

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McAllister revealed, “Some [mosquitoes] prefer to bite at night when we’re sleeping. Others, those that bite during the day or early evening, have chemicals in their saliva that allow them to bite without us noticing it right away. That way, they can get their meal and leave more disease-causing organisms before the itching starts.”

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So that brings us back to the question of why mosquitoes have developed a taste for our blood. How did it all start? As we suggested earlier, a report published by the Current Biology journal in July 2020 looked to answer those queries. And the researchers’ findings were quite fascinating.

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It’s also worth bearing in mind your own personal level of vulnerability in all this. If you’re a person who seems to suffer more mosquito bites than those around you, it might not just be a case of bad luck. In fact, there could be several explanations as to why the bugs are drawn to you.

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As explained by the Healthline website, mosquitoes have the ability to notice carbon dioxide alterations outside. Given that we release the chemical compound whenever we exhale, that can perk the interest of the bugs. If there’s more of it in the air, they’ll realize that a meal could be just ahead.

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Alongside that, the medical website claimed that your choice of clothing might be significant too. Indeed, mosquitoes are drawn to darker shades when they’re active. So should you have a taste for black shirts or dresses, you could be putting a big target on your back for the blood-sucking bugs.

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In addition, Healthline reported that “body odor” also plays a large role in gaining a mosquito’s attention. When we sweat, we release substances like ammonia and lactic acid through our skin. The Aedes aegypti has a particular interest in those scents, picking them up via a cell known as “Ionotropic Receptor 8a.”

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But down the years, different projects have noted that mosquitoes aren’t drawn towards every type of body odor. For example, the PLOS One journal published an intriguing paper on the subject back in 2011. It stated that a mixture of certain “microbes” on a person’s skin could put the insects off biting them.

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However, some four years later, the journal shared another report that revealed mosquitoes were interested in scents coming from identical twins’ hands. For you see, Healthline noted that our genetic structure is responsible for the smell of our sweat. So if a relative is consistently nibbled thanks to those odors, we could be in danger of suffering the same fate.

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Meanwhile, Healthline brought up a couple of other suggestions as to why mosquitoes might be more attracted to certain people. The website reported that an individual’s “water vapor” measurements and body temperature could be factors to consider. Incredibly, the bugs have the ability to sense those readings when they approach us.

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Should our bodies give off the right amount of heat for the mosquito, it could make its move. From there, the website intimated that the blood-sucking pests were capable of remembering what kind of person they’d fed on. With that in mind, you might be at risk of more bites in the future.

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And if that wasn’t enough, an old report from 2002 had some concerning results for fans of alcoholic beverages. The paper was published in the Journal of the American Mosquito Control Association. It revealed that the bugs took more of a liking to beer drinkers than those who steered clear of alcohol.

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Yet a certain group of individuals could be at a higher risk than most. Healthline stated that expectant mothers have been known to draw the interest of mosquitoes. This potentially ties back to the points about carbon dioxide output and body heat. After all, the baby bump adds some extra strain to daily activities.

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As for how all our woes with mosquitoes started in the first place, let’s redirect our focus back to the report in the Current Biology journal from July 2020. The study was conducted by 19 researchers, with Noah Rose helming proceedings. He held a position at Princeton University, where he analyzed “mosquito population hosts.” To begin with, the team assembled eggs of mosquitoes from 27 different areas throughout Africa.

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Specifically, they targeted regions to the south of the Sahara Desert. A few of the areas were far away from populated communities, while others could be found close to towns that boasted “over 2,000 people per square kilometer.” As for the type of mosquito that was chosen for the study, Rose and company opted for the Aedes aegypti.

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Once everything was in place, Rose and his fellow researchers then got to work on the project, closely studying their subjects. They discovered that there were a couple of explanations as to why the mosquitoes had a fondness for human blood over other animals. The reasons were “population density” and “dry season intensity.”

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To explain more, Rose sat down to talk with Inverse in July 2020 following the publication of the paper. During their conversation, he revealed that the mosquitoes would only show an interest in local communities if numbers in that settlement reached a certain point. And the researcher opened up about some of the expectations that his team had beforehand as well.

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Rose told the website, “We thought that mosquitoes that live in the forest with lots of different available animal hosts would be less attracted to humans. And mosquitoes living around people would be more attracted to humans. [But] human population density effects only kicked in when population densities got very high.”

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Yet it could be argued that the weather was the deciding factor in driving the mosquitoes on to bite people. As stated in the report, the Aedes aegypti go through a certain process when birthing their offspring. Water plays a crucial role in that, so once the moisture dries up, they look to other sources.

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The paper explained, “Aedes aegypti lay their eggs on wet substrate just above the water line in tree holes, rock pools, or artificial containers. If the eggs remain wet, they can hatch immediately. However, eggs laid in wild areas at the end of the rains must pause development and survive the duration of the dry season until rain returns.”

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“[That’s] a particularly difficult challenge when the dry season is long and hot,” the paper continued. “[But] human water storage helps Aedes aegypti in harsh environments by providing a year-round aquatic niche for larval development.” As a result of that, Rose and company claimed that the aforementioned “dependence” encouraged them to target people.

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But over the course of the research, Rose and his team uncovered an additional piece of information. While taking a closer look at the genetic structure of 375 mosquitoes, they noted an alteration “in a few chromosomal regions.” As it turned out, this tied into their attraction for human blood.

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For you see, all of those mosquitoes came from areas across the world where the human population was high and dry seasons were prevalent. With that in mind, the group made a concerning forecast at the end of the paper. As African communities continue to get bigger, they claim that the bugs might zone in on them within the next three decades.

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And if that wasn’t worrying enough, Rose brought up another point. He told Inverse, “We don’t know if this will look like more willingness to bite humans, or the evolution of strong preference for humans to the exclusion of other animals.” Regardless of the answer, the researcher believes that plans must be put in place for the years ahead.

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The biggest concern arguably relates to the storage of outside water in those towns. As we’ve already seen in the study, that could cause a host of problems going forward if it isn’t rectified. In Rose’s mind, though, there are positives to take from his team’s prediction about the future.

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“If we make sure that people in these rapidly growing cities have access to safe, clean water,” Rose said. “And we try to make sure there isn’t lots of open standing water in containers, then we can disrupt the ecology of this disease-spreading mosquito. [Our paper] can inspire us to act in anticipation of these possible challenges.”

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Meanwhile, you and your family can take similar precautions at home if mosquitoes are loitering in the area. Indeed, Healthline suggests that any outside objects that collect water must be emptied or removed. As for ornamental external furniture such as bird baths, the website advises you to keep them as clean as possible.

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Alongside that, a change of clothes might be a good idea too. As we mentioned earlier, mosquitoes are drawn to dark shades, so you should consider adopting a lighter look. And by sporting longer garments that cover up your arms and legs, it’ll be much harder for the insect to feed on you.

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Healthline also recommends that you should remain indoors during “peak mosquito times.” Over the course of the day, the bugs are said to be more energetic in the morning and evening, with a lull in the afternoon. It might not be the easiest precaution to take, but it could save you from a painful bite.

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However, if the mosquitoes are somehow working their way into your home, you might have to take more serious action. For instance, the installation of a screen could be required to block their access. Once that’s done, it’s always a good idea to keep bug spray handy as well, so long as it contains oil of lemon eucalyptus, DEET or picaridin.

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Unfortunately, though, it’s not always possible to swerve a mosquito bite. If it happens to you, Healthline suggests that you should run the affected area under a hot tap, applying some soap as you go. But the CDC website highlighted an alternative method of treatment.

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The agency claimed that a homemade “paste” could ease the itching from the bite. To make up a batch, you just need some water and a single tablespoon of baking soda. After stirring them together, you’re advised to leave the mix on the irritated bit of skin for roughly ten minutes, before clearing it away.

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Yet as we’ve already discussed, mosquito stings can cause serious issues beyond a simple itch. Indeed, Healthline reported that you might experience symptoms such as headaches and signs of a fever if something’s wrong. In those instances, you must seek out medical assistance to identify the problem before it gets worse.

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