Why Giant Mosquitoes Are Suddenly Swarming Greenland

If you catch a Greenlandic mosquito in your fist, do not relax your fingers. Unless you've clasped your grip so tightly that you fear you've broken skin and then squeezed a bit more, you haven't killed it. When you loosen your grip, the mosquito will simply fly away faster than you can react, a bit battered perhaps, but still able to take a bite out of you.

"They're aggressive because they're desperate," says Lauren Culler an ecologist with Dartmouth's Institute of Arctic Studies who researches Greenland's mosquitoes. "My research here," says Culler, "has found that only 12-15 percent of mosquitoes ever get a blood meal."

Female mosquitoes (only female mosquitoes bite) require a blood meal to lay eggs, and here in Greenland blood meals are limited primarily to caribou (also known as Greenlandic reindeer), musk ox, and sweet blooded visitors from New York City. They're aggressive enough that they can kill caribou calves.

Although we typically associate mosquitoes with warmer climates, the Arctic, except for Iceland which is a bit of an ecological mystery, has fierce, fat, and abundant mosquitoes. Culler and I are in Kangerlussuaq, a dusty inland town of roughly 500 people in Western Greenland, to check out her mosquito ponds, the shallow pools of water where mosquitoes spend three quarter of their lives. Mosquitoes are laid in ponds as eggs, hatch as larva, and pupate or transform from wriggling larva into flying mosquito, at the ponds' drying margins.

Kangerlussuaq means "big ford" in Greenlandic, a reference to the 120 mile fjord, a deep narrow channel of sea between high cliffs that beg to be climbed, that extends all the way to the Davis Straight. Kangerlussuaq is not a traditional settlement—Greenlanders preferred to settle along the coasts—but rather was hewn into existence in the 1940s by the American Air Force as a base of operations during World War II. When the military pulled out in 1992, it sold Kangerlussuaq's airstrip and buildings to the Greenlandic government for a dollar, transforming the town into Greenland's main airport. Apartment houses are still referred to by barrack blocks, and the road to Dr. Culler's mosquito ponds is marked by a section warning visitors not to stray off of the road. The fields that surround it may still contain unexploded ordinance.

Dr. Culler's work focuses on how the arctic's rapidly warming climate, affects mosquitoes and by extension caribou and people. Before climate change, mosquitoes hatched in late May, begin biting in late June, and were all gone by late July. But with climate change there's much more variability.

When mosquitoes emerge is dictated by their incredible sensitivity to temperature. In fact, a Greenlandic mosquito egg won't hatch until it's been frozen and then warmed. Because mosquito ponds are so shallow, they're one of the first things on the landscape to thaw, so in years when spring comes early, the mosquitoes come early.

"In the years when the ponds thaw and they heat up really quickly," says Culler, "the mosquitoes go through their development faster which means there are fewer days to be eaten by a predator. Lab studies, field studies, and population models show that a warming climate means more mosquitoes survive until adulthood."

Culler insists that I came at the right time—at the end of mosquito season—but the prams gracefully sheathed in matching mosquito netting, the mosquitoes that line my tent's rain guard, that swarm around me on a midnight sun hike, and of course the ones that somehow find their way under the mosquito net I wear on my head, make me wish I'd come in December.

More mosquitoes surviving doesn't mean that more will reproduce—they still have to get a blood meal—but it may mean that in a given year there are more mosquitoes on the landscape. That's annoying for me, but life threatening for the region's caribou.

While the biology of a mosquito is driven by temperature, the biology of a caribou is driven by seasonal changes in day length which are unaffected by climate change. Every spring they migrate from the coastal town of Sisimiut, where winters are milder, to Kangerlussuaq to birth their calves. In the past, their cycle was timed so their arrival coincided with when the fields were filled with young, nutritious plants and the mosquitoes were not yet biting. But as the Arctic warms, the plants sprout earlier, leaving the caribou older, tougher, and less nutritious options.

"The animals show up expecting a food bonanza, but they find that the cafeteria already has closed," as Arctic researcher Jeffrey Kerby likes to say.

Meanwhile, the mosquitoes have reached adulthood and are ready to dine. Unlike humans who can swat mosquitoes, wear nets and repellants or retreating indoors, caribou only have one form of defense of mosquitoes: they can run. They'll run to windy locations, and even on top of glaciers to avoid mosquito harassment.

"Every moment that a caribou spends avoiding insects is another minute that they're not doing what caribou need to do so that they feed so that they can successfully raise calves," warns Culler.

In Arctic Canada this asynchronisity between the caribou and their rapidly changing environment has seen population declines of 93 percent: from 472,000 in 1986 to 32,000 in 2010. This isn't just bad for the caribou but also for the humans that depend on them. Caribou are key subsistence resource for communities throughout the arctic—in 2011, the last year for which there is verified data; Greenlanders hunted 12,052 caribou in a country where there are only 56,000 people.

In addition, the one bright spot of Greenlandic mosquitoes'—that they don't carry diseases like malaria or West Nile—may also be challenged by climate change. It's not that Greenlandic mosquitoes will start carrying diseases but rather that as the Arctic warms, the landscape becomes better suited for other types of mosquitoes that do carry diseases.

Globally, mosquitoes and their diseases kill more people than any other animal, and increasingly there's the belief that we'd be better off without them: a 2010 article in Nature reached the consensus that there isn't anything that mosquitoes do, from pollination to providing food for birds and bats, that couldn't be filled by other species. Florida residents are waiting for an FDA decision on whether or not to release a genetically altered mosquito created by the UK based company Oxitec which has altered two genes in male Aedes aegypti mosquitos so that when they breed with wild females the resulting offspring die as larval.

But Culler cautions that in the arctic there are only a handful of species within each niche and it's not really well understood what would happen if the mosquitoes disappeared. For example, beetle larvae feed on mosquito larvae when they're young, and mosquito harassment is a big factor in keeping caribou herds moving and not overgrazing.

As Culler and I drive towards town swatting the handful of mosquitoes that have made it into her pickup truck she remarks that mosquitoes are facing their own pressures. For reasons that remain unclear, surface water in Greenland is beginning to dry up. Of the ten ponds that she keeps track of, at least three have completely disappeared. This hasn't impacted her research—Greenland has plenty of mosquito ponds and mosquitoes left to study—but even knowing the risks it gives me itchy hope that one day the mosquitoes will disappear.

Correction: An earlier version of this story says Kangerlussuaq was founded in the 1930s; it was founded in the 1940s.