Published May 28, 2009 05:54PM
The most dangerous animal on the planet isn’t a snake, bear, or tiger. In fact, it’s scarcely the size of a thumbtack. It’s the mosquito–the very same buzzing nuisance that ruined your last hiking trip also kills up to three million people every year by infecting them with malaria. Here’s how the uniquely equipped mosquito zones in its warm-blooded victims, leaving welts, itchy skin, and sometimes, devastating diseases in its wake.
Detection
It’s tough to evade a thirsty skeeter, and no wonder. Mosquitoes use ultra-sensitive antennae on their foreheads to track clouds of carbon dioxide released in their prey’s breath. Meanwhile, their palps—akin to the human nose—sniff out body odor, soap, and perfumes. Uniquely shaped eyes also discern changes in contrast and motion (experts think they work best in low light). To top it off, mosquitoes can also sense infrared radiation (i.e., body heat), which might explain how efficiently they can hone in on the tiniest section of exposed skin, notes Don Barnard, an entomologist in the U.S. Department of Agriculture’s Mosquito and Fly Research Unit. This could also be why the bugs seem more attracted to dark clothing than light—dark colors retain more heat.
Life Cycle
It’s true: Only female mosquitoes bite. “The sole purpose of a blood meal is to lay eggs,” says Joseph Conlon, an entomologist and technical advisor for the American Mosquito Control Association. During their three-week lifespan, mosquitoes will typically bite and lay eggs two to three times. This high rate of reproduction—and in turn, genetic adaptability—is the main reason for mosquitoes’ success. Each of the 176 different species of mosquito found in the United States requires an area that floods periodically for their eggs to hatch. As a result, mosquitoes are most active in the spring and early summer. Once exposed to water, hatchling larvae emerge in one to two days. It takes another five to 12 days for larvae to morph into pupae and adult mosquitoes.
Experts think climate change might have a significant effect on the bugs’ life cycle. Increased precipitation could give mosquitoes more territory in which to bite and breed, says Conlon. What’s more, species in temperate climes will be less subject to the challenges of winter, and therefore, active when they used to have to hole up to wait out the cold.
Infection
Blood-borne human pathogens like malaria and West Nile Virus have co-evolved with mosquitoes. “Mosquitoes find infected host animals [birds , in the case of West Nile], extract blood that contains the pathogens, and provide a place for the pathogen to develop and increase in number,” explains Barnard. “Then they retransmit the pathogen by feeding on other organisms.” Mosquitoes and host animals are unaffected; they simply act as transmission corridors and storehouses for the pathogen.