Are mosquitoes necessary?

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Sounds of a Minnesota summer: the echo of loons, a sizzling grill, a crackling bonfire — and the smacking noise of friends fending off determined mosquitoes.

I doubt there is a creature more loathed the world over than mosquitoes. Understandably, the most common question asked of an insect scientist (like me) is: "What are mosquitoes good for, anyway?" Let's take a moment to address that question and learn how these fearsome creatures live.

Mosquitoes begin life as eggs. A pregnant female will visit standing water in wetlands, puddles or used tires, where she gently lays a raft of eggs — sometimes hundreds per batch. If all goes well, the eggs hatch a few days later. If the puddle they were laid in dries up, mosquito eggs have the remarkable ability of remaining viable in the soil for years until conditions are right for hatching. Similarly, eggs laid in the fall are programmed to wait out winter.

Newly hatched mosquitoes, known as larvae, begin an active and perilous existence under water. These small, wriggling insects frantically swim between rocks, logs and other surfaces colonized by bacteria and algae, a mosquito larvae's favorite foods. At all times, larvae are at risk from lurking predators. Many species of small fish, and countless aquatic insects, like baby dragon- and damselflies, see mosquito larvae as food. These soft, defenseless larvae are like gummy bears in a classroom of kindergartners.

After a couple of weeks, surviving larvae transform into a nonfeeding stage called a pupa, which lasts only a few days. During this period, the insides of mosquitoes melt into seemingly disorganized goo, but amazingly reorganize into the six-legged, winged, flying adult that we are too familiar with — creatures that look and behave nothing like their former selves. This dramatic transformation is called complete metamorphosis.

Female mosquitoes, with simple, threadlike antennae, also visit flowers to drink nectar. However, females have a special objective which requires a more powerful diet. Her eggs cannot develop without her taking a meal of one of Earth's most nutritious substances, blood. Finding this all-important meal will be the most dangerous mission of her monthlong adult life.

To secure a future for their offspring, female mosquitoes smell the air with their antennae, searching for a telltale sign of an animal nearby — carbon dioxide (CO2), a molecule that you and all animals exhale with every breath. Flying toward a cloud of CO2 gets her close enough to search for other scents which reveal specifics, like, is this a bird, a mammal, a reptile? If the animal is what she is looking for, the female will stealthily approach and attempt to nab a few drops of precious blood, the only recipe to grow her offspring and begin the cycle once more.

Of the 51 mosquito species in Minnesota, 24 take blood from humans. When your backyard barbecue is interrupted by a buzzing battalion, it is one of these maternal animals trying to make you a part of her birth story!

The necessary meal of blood is how mosquitoes have gained their reputation. While the female's ultrathin mouthparts enter your skin, probing for a vessel, she injects a small amount of saliva to encourage blood flow. The saliva can do more than make you itch.

Several parasites and microbes have evolved to depend on mosquitoes for transport between host animals. As difficult as it is for humans to accept, the spread of disease between organisms is one of mosquitoes' most important contributions to the environment.

Have you ever wondered what controls the number of top predators, since nothing eats them? Of course, the supply of their food plays an important role, but so does the spread of disease. Mosquitoes are experts in this category. Their activity balances nature by ensuring that certain species, including many top predators, do not become overly abundant.

Humans haven't escaped the influence of these Earth-shaping insects and their pathogenic hitchhikers. Anthropologists have evidence that historically, mosquito-vectored diseases have led to more human deaths than all other premature causes combined. More than cancer, heart disease, war, famine. So effective are these little creatures at controlling top predators that, until recently, important ecosystems such as the Amazon rainforest were protected from human development by the only thing that could stop us, mosquitoes!

Mosquito-borne illnesses are not common in Minnesota today. We have the advantage of cool weather, modern repellents and clothing that offers protection. Some places on Earth are less fortunate. Tropical environments with year-round mosquito pressure and impoverished peoples are especially susceptible to mosquito-transmitted ailments. The World Health Organization estimates that mosquito-borne diseases are responsible for about 750,000 deaths annually, 600,000 from malaria alone.

It is remarkable how minuscule animals play an outsized role in our lives. One adult female mosquito weighs 2.5 milligrams. I weigh 180 pounds. You would need to amass 32,658,624 mosquitoes to balance the scale against me. Yet this creature 30 million times smaller than me has altered human history, changes our behavior and, in partnership with pathogens, works to balance natural ecosystems.

Just like every other organism on Earth, mosquitoes are important, but for reasons we may have difficulty reckoning with.