There are more than 110 trillion mosquitoes on Earth. That’s almost 16,000 for every person! They live on every continent except Antarctica.

Mosquitoes are famous bloodsuckers. So you might be surprised that the insects’ main food source is nectar, a sweet liquid from plants. There are more than 3,500 mosquito species. Different species feed on blood from different animals. Only a small portion of species feed on human blood.

Male mosquitoes don’t bite at all. That’s the job of female mosquitoes—just before they lay eggs. When temperatures rise above 50°F (10°C), female mosquitoes lay eggs in watery areas, like ponds, puddles, or rain-filled flowerpots. But before they do, the insects need a blood meal. They search for an animal, like a human, and use their tube-shaped mouth like a straw to suck up blood.

This is where the problem begins.

When a mosquito bites, it injects saliva into its victim. If the mosquito has recently bitten a person infected with a disease like malaria, that spit can contain a tiny germ that causes the disease. When this germ enters a person’s blood, they become infected too.

That’s how, bite by itchy bite, millions of people come down with malaria each year. Millions more are infected with other deadly diseases, such as dengue (DENG-gee) and West Nile virus.

More than 110 trillion mosquitoes live on Earth. That’s almost 16,000 per person! They live on every continent except Antarctica.

Mosquitoes are famous for sucking blood. So this next fact might surprise you. That’s not the insects’ main food source. It’s nectar. This sweet liquid comes from plants. There are more than 3,500 mosquito species. Different species feed on blood from different animals. Only a small number feed on human blood.

Male mosquitoes don’t bite at all. That’s the job of female mosquitoes. They bite only before they lay eggs. Temperatures must rise above 50°F (10°C). Then female mosquitoes lay eggs in watery areas. These include ponds, puddles, or rain-filled flowerpots. But the insects need a blood meal first. They search for an animal, like a human. Each mosquito’s mouth is shaped like a tube. They use it like a straw to suck up blood.

This is where the problem begins.

A mosquito bites a person. The person may be infected with a disease like malaria. Then the mosquito bites someone else. It injects its saliva. The spit contains a tiny germ from the person who was infected. It causes the disease. This germ enters the second person’s blood. And they get infected too.

That’s how millions of people catch malaria each year. It happens one bite by itchy bite. Millions more are infected with other deadly diseases. They include dengue (DENG-gee) and West Nile virus.

Humans’ battle with mosquitoes isn’t new (see Malaria-Stopping Strategies, below). As long as we have walked on Earth, mosquitoes have been biting us—and infecting us with diseases. For most of that time, people thought the illnesses were caused by warm, moist air. That made sense because the diseases were most common near swamps, where mosquitoes like to breed.

In the late 1800s, scientists discovered the tiny parasite that causes malaria and learned it was spread by mosquitoes. Researchers went on to develop drugs to help treat the disease. They also created insecticides, chemicals that can kill mosquitoes. Thanks to these innovations, malaria was mostly gone from the U.S. by the 1950s.   

But the fight against malaria has continued in much of Africa and other places with tropical climates, where mosquitoes lay eggs year-round. In these areas, people spray their homes with insecticides. They sleep under mosquito nets to prevent the insects from biting them at night.

Over time, the efforts helped. Malaria remained a major killer in Africa, but by 2019, deaths from the disease dropped to the lowest number in history.

Humans’ battle with mosquitoes isn’t new (see Malaria-Stopping Strategies, below). The insects have been biting as long as we’ve walked on Earth. But people didn’t think mosquitoes caused illnesses long ago. They thought warm, moist air caused diseases. That made sense. That’s because diseases were most common near swamps. The air there is warm and moist. And that’s where mosquitoes breed.

Then scientists found something in the late 1800s. It was a tiny parasite. It causes malaria. They learned it was spread by mosquitoes. Scientists went on to develop drugs. They helped treat the disease. They also created insecticides. These chemicals can kill mosquitoes. These tools helped. And malaria was mostly wiped out from the U.S. by the 1950s.

But the fight against malaria continued in places like Africa. Mosquitoes lay eggs year-round in tropical climates. People there spray their homes with insecticides. They sleep under mosquito nets. The nets keep the insects from biting them at night.

The efforts helped over time. Malaria was a major killer in Africa. But deaths from the disease dropped. They reached their lowest number in 2019.

Unfortunately, in recent years, malaria deaths have gone up again. Why? Scientists are finding some mosquito-fighting strategies are no longer working very well. The reason: Mosquitoes have adapted.

Here’s how that happened: Over time, the chemicals in insecticides have killed many mosquitoes—but not all of them. Some survived, passing down their insecticide-beating traits to their young. Over time, more and more mosquitoes carried traits that protected them from insecticides. As a result, these chemicals are no longer as effective against mosquitoes.

In Africa, mosquito nets have long protected people from the insects at night. But scientists suspect that some mosquitoes there have adapted to bite in the daytime. “It’s a constant cycle,” says Low. “We have a solution, then they adapt to it.”

There’s another problem. Dangerous mosquitoes are moving around the world. Since 2012, a type of mosquito from South Asia has been spreading malaria in African cities. And for the first time in many years, mosquitoes have infected people in parts of Europe with dengue.

In the U.S., several dangerous mosquito species are thriving. They are originally from other areas of the world and are more aggressive than native species. The insects feed more often and bite quickly, making them hard to shoo away in time. These mosquitoes can spread diseases like malaria.

Scientists expect these problems to get worse because of climate change. As temperatures warm, mosquitoes can survive year-round in places that were once too cold for them. That means more parasites and germs that cause diseases.

But malaria deaths have gone up again recently. Why? Some methods to fight mosquitoes no longer work as well. That’s because mosquitoes have adapted.

Here’s what happened: Insecticides killed many mosquitoes. But not all of them. Some survived the chemicals. They passed down this trait to their young. So more and more mosquitoes had this ability. It protected them from insecticides. Now these chemicals aren’t as good at killing mosquitoes.

Mosquito nets have long been used in Africa. They protected people from the insects at night. But scientists suspect mosquitoes have adapted. They now bite in the daytime. “It’s a constant cycle,” says Low. “We have a solution, then they adapt to it.”

There’s another problem. Dangerous mosquitoes are moving around the world. A mosquito from South Asia has been in Africa since 2012. It’s been spreading malaria in cities there. And mosquitoes have infected people in Europe with dengue. This had not happened for many years. 

Several dangerous mosquito species are thriving in the U.S. They are from other areas of the world. They’re more aggressive than native species. The insects feed more often and bite quickly. That makes them hard to shoo away in time. These mosquitoes can spread diseases like malaria.

Scientists think these problems will get worse. That’s because of climate change. Some places were once too cold for mosquitoes. But temperatures are warming. So the insects can now survive in many places year-round. That means there are more parasites and germs that cause diseases. 

Luckily, scientists are hard at work developing solutions. Eric Ochomo is an entomologist, or insect scientist, in the East African country of Kenya. Malaria is a constant threat there. He’s testing out new and improved tools to fight mosquitoes.

One tool is an indoor device that sends out a chemical into the air. The chemical confuses mosquitoes so they don’t bite. Ochomo is also testing an outdoor device that lures the insects with sweet liquid, then kills them with poison. Using several strategies is important, Ochomo says. That makes it less likely that mosquitoes will adapt.

Other researchers are breeding male mosquitoes that can’t reproduce. In the wild, these mosquitoes could help lower the mosquito population since they can’t reproduce. And in late 2023, a new malaria vaccine was introduced in parts of Africa. Scientists expect the shot to reduce malaria deaths, especially in kids.

There are ways people like you can help (see How You Can Help, below). Ochomo hopes more kids become scientists when they grow up, so they can help protect humans from mosquitoes.

“There are a lot of problems we still don’t know how to solve,” he says. “We need all the brains we can get!”

Luckily, scientists are working on solutions. Eric Ochomo is an entomologist. That’s an insect scientist. He works in the East African country of Kenya. Malaria is always a threat there. He’s testing new and better tools to fight mosquitoes.

One tool is an indoor device. It sends out a chemical into the air. The chemical confuses mosquitoes. Then they don’t bite. Ochomo is also testing an outdoor device. It lures the insects with a sweet liquid. Then it kills them with poison. People must use many methods, says Ochomo. That makes it less likely that mosquitoes will adapt.

Other scientists are raising special mosquitoes. The males can’t reproduce. They could be set free into the wild. They’d help lower the mosquito population. And there’s a new malaria vaccine. It was first used in Africa in late 2023. Scientists think the shot will reduce malaria deaths, especially in kids.

There are ways people like you can help (see How You Can Help, below). Ochomo hopes more kids become scientists when they grow up. Then they can help protect humans from mosquitoes.

“There are a lot of problems we still don’t know how to solve,” he says. “We need all the brains we can get!”