Sometimes, when it rains or when they feel the urge to migrate, spiders get out their little silk knapsacks, and balloon away. This ballooning behaviour is well understood by spider scientists, but researchers have recently discovered that electric fields can not only trigger the behaviour, but also provide lift – even without the slightest breeze.
"When one thinks of airborne organisms, spiders do not usually come to mind," explained researchers Erica Morley and Daniel Robert from the University of Bristol, in their paper. "However, these wingless arthropods have been found 4 kilometres [2.5 miles] up in the sky, dispersing hundreds of kilometres." They travel via the atmospheric potential gradient (APG), an electric circuit between Earth and the ionosphere - the part of Earth's upper atmosphere that's ionised by solar radiation.
The researchers explain that the idea of ballooning behaviour being caused by this electric circuit was first floated in the 1800's, but had been dismissed not long after, without being tested.
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