One of the smallest creatures on earth is also the world’s deadliest animal: the mosquito. Through their bites, mosquitoes spread dangerous diseases that claim the lives of millions of people every year. Understanding how these tiny predators target humans is the key to finding ways to protect us against mosquito-borne illnesses.

The Deadliest Insect on Earth

Of the 3,500 known mosquito species, about 100 species feed on human blood. Female mosquitoes are the ones that bite, and they do so in order to produce their eggs. This biological instinct makes mosquitoes a threat wherever they are on earth.

While mosquito bites are not inherently lethal, they can transfer deadly diseases to or from the host. Because mosquitoes also bite a wide range of animals, they can transfer diseases from other animals to humans, putting us at greater risk of developing illnesses to which we would not normally be exposed.

What is especially concerning is that mosquitoes are highly adaptable. In fact, mosquitoes have only evolved to target humans in the last 5,000 years. Especially due to climate change, mosquitoes are reproducing more quickly and in less friendly environments. They can thrive in a wide range of habitats, and some have even developed resistance to certain insecticides.

Major Diseases Spread by Mosquitoes

Mosquitoes kill nearly 2.7 million people per year by spreading disease. More than 1 million of these global deaths are caused by infected Anopheles mosquitoes (“malaria mosquitoes”), which transfer the Plasmodium parasite that causes malaria directly into the bloodstream. Mosquitoes are also known for spreading the Zika virus, dengue fever, West Nile virus, yellow fever, and other diseases that threaten human health and claim human lives. While some of these diseases are spread by select species of mosquito, others have been linked to as many as 60 mosquito species.

Mosquitoes Can Smell Humans

Female mosquitoes seek out blood to produce their eggs, and humans and animals are prime sources. Complex research of the neural activity in mosquitoes has determined that mosquitoes choose their bite victims based on odor. Mosquitoes identify blood sources by detecting the unique mixture of chemical compounds that make up a person’s smell. Certain compounds are more common in humans or isolated to humans, and it is likely that these compounds are what lead mosquitoes to intentionally target us.

If scientists can learn to control their sense of smell, or to change the way that we smell to mosquitoes, it will completely change our relationship with these tiny predators. Understanding and learning to control how mosquitoes smell us could save thousands of human lives every year.