It's been a good month for arachnophiles! After heavy rains flooded part of New Zealand's Bay of Plenty, an onslaught of eight-legged evacuees set off for higher ground. A grassy mound typically used as a tsunami evacuation area has been blanketed in a silky web.

When spiders need to get out of dodge fast – say, during a flood – many of them will use a tactic known as "ballooning". By shooting a silky strand skyward, the spiders can sail to safety on the back of the wind. Exactly where they land depends on which direction the breeze takes them, and occasionally they arrive en masse. 

"There were heaps of little spiders landing on the car, in the car, everywhere – it was like something out of Harry Potter," Tauranga resident Kirsten Green told The New Zealand Herald.

While the resulting giant cobweb might look a little creepy, it's nothing to be concerned about, nor is it a sign of a spider population boom. This is the same phenomenon that turned Wagga Wagga in Australia into a "ghost town" back in 2012:

It also brought "black raindrops" to Brazil the following year:

This reverse-parachuting also helps spiders colonise new territory, but it can be a risky manoeuvre. Many of the individuals that take to the skies will be eaten by birds or killed by rough weather, for example.

Experts urge anyone who encounters a ballooning event to remember that these animals are beneficial to ecosystems, and not inherently dangerous to people. 

"There's no need to disturb the web," added Canterbury Museum curator and spider expert Dr Cor Vink. "It's not there to catch anything. It's just spiders, wandering around."

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