Despite the temperature being hot as blazes, mid-August is still considered the end of the swimming season in Japan. In our area of the Seto Inland Sea, it used to be said that after O-bon (around Aug. 15) the enko (sea nymphs) come out and can grab your legs and pull you down under the water to drown you. But these days the Japanese have abandoned that old-fashioned myth for the new-fashioned one — that the jellyfish come out after O-bon. So no one in their right mind would go swimming now.
But, having lived on a small island in the Seto Inland Sea for 15 years, I can tell you with confidence that the jellyfish have no idea when O-bon is. They do not have specialized jellyfish watches cinched around their slippery bodies that beep on Aug. 15 every year to inform them it is time to come out. The jellyfish are not waiting at the start gate like race horses, waiting to burst forward when the O-bon bell rings. . . . "And they're off! The jellyfish have surged out of the gates and are racing toward the beach where they hope to sneak up on swimmers and sting them!"
Believe me, jellyfish are not Buddhist. They do not know their ancestors, and they could care less about O-bon. They have not passed a math test, let alone taken a physics class nor studied marine biology. The lunar calendar and tidal charts, however, they're probably experts at.