Subtitles section Play video Print subtitles What's the worst bug on the planet? You might vote for the horsefly or perhaps the wasp, but for many people, the worst offender is by far the mosquito. The buzzing, the biting, the itching, the mosquito is one of the most commonly detested pests in the world. In Alaska, swarms of mosquitoes can get so thick that they actually asphyxiate caribou. And mosquito-borne diseases kill millions of people every year. The scourge that is the mosquito isn't new. Mosquitoes have been around for over a hundred million years and over that time have coevolved with all sorts of species, including our own. There are actually thousands of species of mosquitoes in the world, but they all share one insidious quality: They suck blood, and they're really, really good at sucking blood. Here's how they do it. After landing, a mosquito will slather some saliva onto the victim's skin, which works like an antiseptic, numbing the spot so we don't notice their attack. This is what causes the itchy, red bumps, by the way. Then the bug will use its serrated mandibles to carve a little hole in your skin, allowing it to probe around with its proboscis, searching for a blood vessel. When it hits one, the lucky parasite can suck two to three times its weight in blood. Turns out, we don't really like that too much. In fact, humans hate mosquitoes so much that we spend billions of dollars worldwide to keep them away from us. From citronella candles to bug sprays to heavy-duty agricultural pesticides. But it's not just that mosquitoes are annoying, they're also deadly. Mosquitoes can transmit everything from malaria to yellow fever to West Nile virus to dengue. Over a million people worldwide die every year from mosquito-borne diseases, and that's just people. Horses, dogs, cats, they can all get diseases from mosquitoes too. So, if these bugs are so dastardly, why don't we just get rid of them? We are humans after all, and we're pretty good at getting rid of species. Well, it's not quite so simple. Getting rid of the mosquito removes a food source for lots of organisms like frogs and fish and birds. Without them, plants would lose a pollinator. But some scientists say that mosquitoes aren't actually all that important. If we got rid of them, they argue, another species would simply take their place and we'd probably have far fewer deaths from malaria. The problem is that nobody knows what would happen if we killed off all the mosquitoes. Something better might take their spot or perhaps something even worse. The question is, are we willing to take that risk?