As far as we know, humans are the only living things that wear watches.

But we aren’t the only ones that can tell time.

Earth’s movement sets the rhythms of countless biological clocks.

The 24 hour solar period winds cellular gears controlling sleep, hunger, and metabolism

in creatures ranging from jellyfish to elephants.

And our 365-and-a-quarter-day journey around the sun regulates cycles of seasons, harvests,

and migrations.

But the phases of our planet’s nearest neighbor also have a surprising pull on biological

rhythms.

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For many species the moon’s glow is a cue that’s crucial to their survival.

Vampires and emo teenagers aren’t the only ones who find moonlight romantic.

Lots of animals use the 29-and-a-half day lunar cycle to sync up when it comes to finding

a mate.

Triggered by the full moon, impalas roar, which in turn triggers all their female mates

to begin ovulation.

Using a common signal like this ensures every member of a species goes looking for a partner

at the same time.

Lunar cycles are especially important in the sea.

Marine bristle worms live on rocky shorelines, where they rise to the water’s surface under

the dim light of the new moon.

The worms mass together, swirling around one another and release their gametes in sync.

This big mating party increases the chances that any one worm will contribute to the next

generation.

Some eels also reproduce all at once, and rely on the dim light of the new moon to avoid

predators.

The moon also controls the tides, and that pull can help some animals’ eggs and larvae

develop and survive.

Fish called grunion lay their eggs high up on beaches during high tides, where the sand

protects the eggs as they develop.

They hatch when the next cycle of high tides washes them out to sea.

But what *controls* these living lunar cycles?

These species must have an inner moon clock.

When scientists raised marine worms in constant light or darkness, they didn’t try to reproduce.

But when they gave them artificial light on a lunar schedule, the worms did their mesmerizing

mating dance.

The scientists found special neurons in the worms’ brains that respond to light, linked

to timing genes that control these lunar behaviors.

The moon seems to act like a signal that supercharges the worms’ desire to mate when the light

at night is just right.

But the moon is more than just a clock.

It transforms ecosystems.

The full moon is 100 times brighter than the new moon.

This lets animals see their prey, forage, and navigate better.

But all that light can be risky.

Many species of frogs avoid calling to their friends during the full moon, since the extra

light makes it more vulnerable to predators.

And all the manmade light sources now flooding the night could provide a fake, full-time

full moon that might throw ecosystems out of whack.

So what about us?

Women’s reproductive cycles are about the same length as the lunar cycle, but scientists

think that’s probably just a coincidence.

If human menstrual cycles were, in fact, linked to the moon, why not our great ape sisters?

Now that millions of women are using apps to track menstrual periods, it’s become

pretty clear there’s likely no connection.

So for antelopes, coral, fish, and even wildebeest on the Serengeti, the phases of life are set

by phases up above.

Next time you take a look at that fancy clock in your pocket, remember that you aren’t

the only creature on Earth who relies on a satellite to know what time it is.

Stay curious.

Yes.

Technically speaking, moonlight is just sunlight.

So you can stop typing that comment.

And no, there’s no such thing as werewol