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Most mosquito-eating birds would probably switch to other insects that, post-mosquitoes, might emerge in large numbers to take their place. Other insectivores might not miss them at all: bats feed mostly on moths, and less than 2% of their gut content is mosquitoes. "If you're expending energy," says medical entomologist Janet McAllister of the Centers for Disease Control and Prevention in Fort Collins, Colorado, "are you going to eat the 22-ounce filet-mignon moth or the 6-ounce hamburger mosquito?"
With many options on the menu, it seems that most insect-eaters would not go hungry in a mosquito-free world. There is not enough evidence of ecosystem disruption here to give the eradicators pause for thought.
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As larvae, mosquitoes make up substantial biomass in aquatic ecosystems globally. They abound in bodies of water ranging from ephemeral ponds to tree holes2 to old tyres, and the density of larvae on flooded plains can be so high that their writhing sends out ripples across the surface. They feed on decaying leaves, organic detritus and microorganisms. The question is whether, without mosquitoes, other filter feeders would step in. "Lots of organisms process detritus. Mosquitoes aren't the only ones involved or the most important," says Juliano. "If you pop one rivet out of an airplane's wing, it's unlikely that the plane will cease to fly."
The effects might depend on the body of water in question. Mosquito larvae are important members of the tight-knit communities in the 25–100-millilitre pools inside pitcher plants3,4 (Sarracenia purpurea) on the east coast of North America. Species of mosquito (Wyeomyia smithii) and midge (Metriocnemus knabi) are the only insects that live there, along with microorganisms such as rotifers, bacteria and protozoa. When other insects drown in the water, the midges chew up their carcasses and the mosquito larvae feed on the waste products, making nutrients such as nitrogen available for the plant. In this case, eliminating mosquitoes might affect plant growth.
In 1974, ecologist John Addicott, now at the University of Calgary in Alberta, Canada, published findings on the predator and prey structure within pitcher plants, noting more protozoan diversity in the presence of mosquito larvae5. He proposed that as the larvae feed, they keep down the numbers of the dominant species of protozoa, letting others persist. The broader consequences for the plant are not known.
A stronger argument for keeping mosquitoes might be found if they provide 'ecosystem services' — the benefits that humans derive from nature. Evolutionary ecologist Dina Fonseca at Rutgers University in New Brunswick, New Jersey, points as a comparison to the biting midges of the family Ceratopogonidae, sometimes known as no-see-ums. "People being bitten by no-see-ums or being infected through them with viruses, protozoa and filarial worms would love to eradicate them," she says. But because some ceratopogonids are pollinators of tropical crops such as cacao, "that would result in a world without chocolate".