This footage, filmed in 2008 at Legian Beach in Bali, has re-emerged the past week, and has been going nuts on Reddit and Digg. It's not hard to see why - the video shows what looks to be a harmless handful of sand… until you get closer and realise that the sand is actually thousands of tiny baby crabs, all wriggling to get back to the beach. We can't really decide whether to be disturbed, fascinated, or kinda impressed by the spawning abilities of these minute arthropods.

It's not clear what species of crab this is, but many crabs are well known for their impressive breeding rituals, and this baby crab frenzy is more common than you might think on beaches around the world.

Take the famous red crabs on Christmas Island, which live inland most of the year but migrate to the coast to breed, resulting in a spectacular procession that literally takes over the island.

Once they get to the beach, males and females breed on the sand. And a couple of weeks later, the new mothers head into the water to release thousands of eggs into the ocean, in a crazy moonlit dance. Those eggs will spend the next three to four weeks developing into juveniles.

Most years, very few of them make it back to shore, as a result of being carried away by strong ocean currents or being eaten by predatory fish. But once or twice a decade, when conditions are just right, the baby crabs will arrive back to the beach en masse, forming a living tide that moves across the sand and back to the Island's inland jungles. This is something similar to what you see happening in the video above in Bali.

But even though that footage is impressive, the baby crabs on Christmas Island actually look slightly cooler/more disturbing when they come home, as their colouring makes it look like some kind of foamy pink liquid is taking over the beach. You need to see it to believe it:

So next time you see that crab video appear in your Facebook feed or pop up on Reddit, remember that it took a very special set of circumstances for that squirming mass of spiders with shells to end up in that guy's hand. Nature, you're… awesome?