(Photo: City of Aira)
According to legend, a Japanese general developed spider fighting in the Sixteenth Century as a way to entertain his soldiers. It's still popular in Aira, a city in southern Japan. On the third Sunday of June ever year, 200 kogane spiders (Argiope amoena) fight on wood rods. Altas Obscura describes the rules:
One spider (kamae) stands on the end of a horizontal, wooden pole. A judge places her opponent (shikake) a bit farther down the pole, and places his hand between them, ensuring they are both ready to rumble before allowing the fight to begin. He pulls his hand away and it’s on.
A spider can win a fight in three ways: she can bite her opponent on the abdomen; she can wrap her opponent’s abdomen in thread; or, if her opponent tries to bungee away, she can cut the rival’s thread, causing the loser to tumble to the padded platform below.
The judge has to keep a keen eye on the battle, both to declare a winner and to ensure the spiders don’t seriously damage each other. The majority of the fights are over within 10 seconds, as the judge reaches quickly into the fray to separate them and returns the loser to its disheartened-looking owner. The winner advances to the next round.
Here's a video of a bout between two spiders.