Australia has always been a land of the strange and bizarre. It is home to some of the world's most unique animals, from the kangaroo, to the wombat, to the lovable Tasmanian devil. So the fact that it's raining spiders should come as no surprise.
"The whole place was covered in these little black spiderlings and when I looked up at the sun it was like this tunnel of webs going up for a couple of hundred meters into the sky," says Goulburn resident, Ian Watson. Naturally, he took to Facebook to report the event.
"Anyone else experiencing ... millions of spiders falling from the sky right now?" he wrote on the town's community Facebook page. "I'm 10 minutes out of town and you can clearly see hundreds of little spiders floating along with their webs and my home is covered in them. Someone call a scientist!"
Naturalist Martyn Robinson, from the Australian Museum, had some answers.
According to Robinson, the technique known as "ballooning" is commonly employed by spiders, whose migratory options are limited by their small size. The spiders perch atop vegetation and release a stream of silk that is taken up by the wind, thereby casting them aloft. Robinson says they have been known to fly as high as three kilometers above the ground.
"They can literally travel for kilometers ... which is why every continent has spiders. Even in Antarctica they regularly turn up but just die," Robinson says. "That's also why the first land animals to arrive on new islands formed by volcanic activity are usually spiders."
Apparently, the spiders need just the right weather conditions before taking flight.
"It tends to happen a couple of times per year, usually on clear days with slight winds," Australian resident, Keith Basterfield says. "I was on the Bureau of Meteorology last week and watching the weather for Goulburn and the conditions were just right."
But raining spiders are not restricted to Australia. They have been reported around the world, and scientists have even devised experiments to determine just how the spiders optimize the ballooning technique.
Researchers at Rothamsted Research in the UK conducted experiments a few years back to gauge how the spider's silk stood up to turbulent air. Previous models were based on assumptions that the spider's silk was rigid and straight, and that spiders simply hung at the bottom of the silk during ballooning. But this model didn't work in turbulent air.
The new model allowed for elasticity and flexibility in the spider's dragline. And what they found was that the silk performed like an open parachute, enabling the spider to travel long distances when the winds were right. Researchers hope a better understanding of ballooning might aid scientists in exploring the role of spider dispersals in controlling farmland pests.
"Spiders are key predators of insects and can alleviate the need for farmers to spray large quantities of pesticide," says Andy Reynolds, a Rothamsted Research scientist. "But they can only perform this function in the ecosystem if they arrive at the right time. With our mathematical model we can start to examine how human activity, such as farming, affects the dispersal of spider populations."
