Why Do Mosquitoes Bite?

​​Why & How Do Mosquitoes Bite?

Mosquitoes are one of the deadliest insects in the world for humans. They transmit a large number of diseases, as well as creating much irritation and suffering. Recent estimates have put the number of deaths mosquitoes are responsible per year at 725,000.

However, considering the immense problems mosquito bites cause, not many people know why, or how, these bloodsucking insects bite us.

In this article, we are going to investigate all there is to know about what happens before you feel that telltale itch.

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Why Do Mosquitoes Bite

Why Do Mosquitoes Bite Humans?

Fortunately, human blood is not standard mosquito nutrition. Although, after being bitten numerous times, it may certainly seem so. Most of the time, a mosquito’s diet is typically composed of plant juices and nectar.

In fact, there are over 2,700 different types of mosquito and only certain species are bloodthirsty. Surprisingly, it is only the females who bite and feed on our blood. The female mosquito is the only one equipped with the necessary mouth parts needed to suck blood.

Female mosquitoes bite humans and animals, to obtain all of the nutrients that they need to successfully breed. Some types of mosquito do not need a blood meal, while others require it to begin egg production. Then there are those that produce their first eggs without the need for a blood meal, but require one for further batches.

Feeding on blood provides female mosquitoes with more concentrated nutrients than those provided by plants. Furthermore, blood contains important proteins. These proteins enable them to efficiently produce eggs, or lay further batches.

Although this is the long-accepted science behind why mosquitoes bite humans, it has also been recently suggested that blood meals provide restorative qualities to mosquitoes. During a study at the University of Cincinnati, researchers observed that dehydrated female mosquitoes were much more likely to bite humans than those with normal water levels.

Given the trend for global warming, with higher temperatures and lower humidity levels, this could seriously impact biting and disease transmission rates, increasing the number of human deaths.

With such a large number of species, there are many different types of mosquito that will bite humans. For some, people are their preferential host, while for others we are merely a convenience.

Different regions and temperate zones are home to various species of mosquito. However, the most serious vectors of disease for humans can be reduced to just three types. These three most problematic types are: the Aedes mosquito, the Anopheles mosquito and the Culex mosquito.

The Aedes female mosquito relies on human blood for producing eggs. Female mosquitoes live on average for several days, but can survive for up to several weeks. This cycle of mating, biting then laying eggs continues for the duration of their lifespan. This allows plenty of opportunities for older female mosquitoes to become vectors of deadly diseases, spreading the virus from host to host.

The Aedes can be responsible for transmitting yellow fever, Dengue fever and filariasis. Sub-species of Aedes mosquitoes can be found in both tropical and subtropical areas, making it one of the most widespread mosquitoes in the world. In fact, its presence has been registered on every continent, apart from Antarctica.

The Anopheles is the main vector for malaria. Its subspecies, Gambiae, is infamous for transmitting the deadliest form of the disease. Anopheles mosquitoes can be found in most regions of the world. They can disseminate malaria even outside of tropical areas, where it had previously been wiped out. As a result, there is a constant threat of reintroduction of the disease from the Anopheles.

The Culex mosquito is considered the least lethal of this selection. Their main choice of host is birds, making it less likely that they will bite humans in comparison to the other two breeds.

They are, however, opportunists and will bite humans when nearby. This is especially the case when there’s a decline in bird numbers. The Culex is extremely dangerous for people, as it is very often a vector for malaria, West Nile virus and filariasis.

What Other Animals Do Mosquitoes Feed On?

The types of mosquito that bite are in fact, selective feeders. Each breed has its own preferences. Some species prefer monkeys, while others go for birds or humans. It really all depends on the mosquito species and what hosts are available in its area. The majority have a flight range of one to three miles, but some will travel further for a blood meal.

Mosquitoes can, and will, bite almost every animal alive. They have even been known to bite fish if they stay exposed long enough above the surface. Although mosquitoes may bite other animals outside of their normal preferences, this behavior is usually forced.

Such atypical behavior may occur for several reasons, and it can have disastrous ecological outcomes when particular animal populations become new targets. At certain times of the year, when the mosquito population becomes prolific, increased competition can cause mosquitoes to bite other animals or humans.

Defense activity can also push mosquitoes to feed on other types of animals. Hosts such as birds, may respond to greater numbers of mosquitoes in their habitat by picking them off each other. This will cause mosquitoes to seek out other nearby sources of blood that are more easily available. Either way, the more mosquitoes there are vying for blood meals, the more their hosts will be on their guard and likely to respond.

Habitat change is another reason mosquitoes may switch host prey. Deforestation can destroy entire ecosystems, wiping out certain species from whole areas. If mosquitoes can no longer find their preferred animal in their vicinity, they will choose another. This can be dangerous, as whole populations of mosquitoes may target humans or creatures that were previously spared.

The consequences include an increased risk of disease transmission, stress and added discomfort to both humans and livestock. When deforestation is carried out for additional living areas, humans are in line to become replacement hosts.

Aside from deforestation, natural disasters may also produce similar scenarios. Whenever a particular host population is threatened, the mosquitoes that depend on it will search for other nearby hosts.

How Do Mosquitoes Bite?

Female mosquitoes have extremely complex mouthparts that enable them to extract blood from their hosts. All mosquitoes have a palpus mouth part, but only females have a proboscis. The proboscis is a long, pointed mouthpiece, specifically designed for piercing the skin and removing blood.

In order to bite through the skin and extract blood, the female mosquito needs to first locate her host. Several factors are known to attract mosquitoes to humans including heat, carbon dioxide, perspiration and body odor.

Once a target has been selected, the mosquito lands on her host and pierces the skin with her proboscis. The inner mouthparts, known as mandibles and maxillae, puncture the outer layers of the epidermis. The jagged ends of the maxillae give the mosquito grip to push further beneath the skin.

Then she inserts two tubes under the skin into the ruptured blood vessel. These tubes are called the labrum and the hypopharynx. The labrum is used to pump the blood up, while the hypopharynx transfers saliva to the host which serves as a lubricant. The excretion also contains anticoagulants to prevent the blood from clotting and enabling flow up the labrum and into the mosquito’s abdomen.

A mosquito will feed for up to around four minutes or until interrupted. Often the host only realizes they have been bitten once the mosquito removes the proboscis, and prepares for take-off.

The residual saliva can cause itchiness, allergic reactions, and even block the immune system. This is particularly damaging when the mosquito in question is carrying a disease. In blocking the immune system, the saliva gives any disease a head start to getting established within the host.

Summary

Mosquito bites cost the lives of thousands of people every year. These bloodsucking insects will happily bite both humans and animals in order to produce their eggs. While not all types of mosquito need a blood meal to reproduce, those that do aren’t terribly selective about who they choose to bite. 

Female mosquitoes are the only sex which will bite animals and consume blood. As a result, they have complex mouth anatomies that facilitate the extraction of blood. In fact, they are so highly specialized that we often don’t realize we have been bitten until after they have left.

Mosquito bites may be incredibly dangerous, and somewhat irritating, but the method behind them is fascinating, nonetheless.

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