Vines were once just something that Tarzan swung on through the jungle. Then they got ambition. Now they're on the move, threatening to take over the world. 

Tarzan's lianas, those swinging vines, are the freeloaders of the rainforest, twining themselves around trees and shimmying into the sunshine. Their fat green leaves hog the light, while their roots scarf up water and nutrients. Trees burdened with lianas often succumb prematurely, and their collapse drags down their neighbors.

Up to half of all plant species in a typical rainforest are vines. But as rainforests are fragmented by agriculture and logging, vines are proliferating, even in undisturbed forests. Their growth spurt, says William Laurance, a biologist at James Cook University in Cairns, Australia, may be fueled by rising levels of atmospheric carbon dioxide, which allows them to outcompete slower-growing trees.

In the southeastern United States, the invasive kudzu vine swallows more than 100,000 football fields' worth of land each year. Introduced as an ornamental in 1876, kudzu can grow a foot per day and smothers everything in its path. As the planet warms, it's heading north, snaking into Ohio, Illinois, Indiana, New Jersey, and as far as Ontario, Canada.

In fact, kudzu may have a role in creating the warm weather in which it thrives. A paper published in the journal New Phytologist shows that as kudzu invades a pine forest, it increases the amount of carbon released from the soil by 28 percent. That's because the plants' leaves and stems are more easily broken down by soil microbes than is pine litter.

So is global warming all a viny conspiracy? Remember that we warned you when the vines encircle your house.