They come every year. After the first spring rain, millions of red, black and yellow crabs swarm out of forests across Cuba. The purpose of the march? To spawn in the waters of the country's southern coast.

It's a stunning sight to be sure, seeing an endless stream of crabs navigating the island with nary a concern for the humans and dangers around them. There are so many crabs afoot that some are routinely crushed by automobiles on the road. That sad truth is a boon for hungry birds but it doesn't pose a threat to the crabs' overall survival. There's just so many of them that it barely makes a dent. (The crabs win a few battles, too, puncturing many a tire before the migration is done.)

And the chaos isn't limited to the roads. Human structures aren't immune from a crab infestation, either. "Thirty to 40 can enter without you even realizing it," Edian Villazon, who runs a food hut opposite the sea, told the Telegraph. "We have to always keep the door shut."

There's just no escaping these crabs when they're ready to reproduce.

Crabs clog roads in Cuba for annual invasion
Millions of crabs swarm over Cuba in the early spring to make it to their spawning grounds.