When the full Moon rises, strange things can happen here on Earth. Oysters snap close. Corals spawn. Zooplankton dive deeper. Seabirds stick to the shore. And lions hunt less.
Several of these behaviors are tied to moonlight; others, to tides. But some have no clear explanation at all.
More than 50 years' worth of shark attack data, for instance, has now found that sharks bite humans more when the Moon is fuller.
"It's not a matter of more light at night for sharks to see. Most shark attacks occur in the daylight," explains ecologist Steve Midway from Louisiana State University.
So what is it? We don't know. The relationship could simply be random – a fluke in the data – or it could be a result of the 'lunar effect'.
The lunar effect is an unproven correlation between the phases of the Moon and the activity of plants and animals here on Earth.
That might sound supernatural at first, but there's good reason to suspect an invisible string from our nearest neighbor is puppeteering life on our planet.
A recent meta-analysis, for example, found compelling evidence that gravitational tides can change the way animals and plants sleep, move, and grow. Although, the exact way in which this happens is still a mystery.
Marine life seems to be particularly influenced by the Moon, and sharks are no exception. Their movements and natural feeding patterns have been tied to lunar rhythms in the past.
Yet sharks aren't the only big animals changing their behavior with the Moon. Surfers are some of the most impacted by shark attacks, and the best conditions for surfing tend to occur more around the full moon.
Perhaps it's our activity around full moons leading to more shark attacks, and if that's the case, it would be good to know how we are triggering such aggression.
"Although this is not firm evidence of shark attacks preferentially occurring during periods of greater lunar illumination (i.e., a full moon), these results are the first global evaluation to report any evidence of shark attacks correlated to moon phase, and as such warrant further investigation," the authors write.
It's also important to note that while terrifying, shark bites are relatively rare. These fish play a vital role in ocean ecosystems as apex predators. Many species are experiencing huge population declines or shifts in their habitats, pushing them closer to more populated areas.
While shark attack incidents are increasing with increasing numbers of people in the waters with them, humans have swum with sharks without incident a lot more often than we realize. Sharks are not known to target humans as prey, but instead, sometimes mistake us for it.
More research is needed to figure out what is going on here because any possibility of reducing such harmful interactions is worth looking into.
In the meantime, swimming in groups and avoiding the water at dawn and dusk can reduce the risk of unfriendly encounters.
The study was published in Frontiers in Marine Science.