JERUSALEM • Swimmers wanting to avoid being stung by jellyfish may want to watch the sky as much as the sea after Israeli researchers found a link between the creatures' arrival and the phase of the moon.
The study found the lunar calendar is a key determinant of when jellyfish arrive on the Mediterranean country's shores.
In the middle of the lunar months - the days before and during the full moon - jellyfish are far more likely to swarm the beach, potentially stinging humans, the research found.
"We were surprised by our findings," said researcher Avi Algazi.
"We knew the moon has a big influence on a lot of things, but we didn't have statistical data on the correlation between jellyfish and the moon."
The research was conducted by the Israel Electric Corporation, in conjunction with the University of Haifa in northern Israel.
Jellyfish are a threat to Israel's power supply as they get sucked into the country's main power station, which uses sea water for cooling.
The researchers looked at when the power station was most badly affected by jellyfish, and correlated it with the moon and water temperatures.
In total, 94 per cent of jellyfish swarms arrived after the middle of the year when the seas are warmer and during the second and third weeks of the lunar month.
The ideal water temperature for jellyfish is between 28.2 deg C and 30 deg C, the research found.
Dr Algazi stressed that the research so far applied only to local conditions, but said he hoped "the results could be checked in other parts of the world".