These flying insects are all too familiar to most people. What’s little known, however, is that only the female mosquito drinks human blood, which is needed in order to make eggs. While mosquitoes are usually just annoying—the itchy bump left from a mosquito encounter is a reaction to its saliva—some unfortunate people find out that mosquitoes can transmit a number of serious diseases, including yellow fever, malaria, filariasis, and dengue. Which is why mosquitoes are considered one of the world’s deadliest animals.
This is another pesky but seemingly benign insect that is actually extremely deadly—as in Black Death deadly. These bloodsuckers are believed to have helped cause the bubonic plague that killed a quarter of Europe’s population during the Middle Ages. As infected rats began to die off, fleas turned to humans for blood, thereby transmitting the disease. And you probably thought fleas were just a problem for Fido.