Most animals, humans included, have bodily rhythms governed by the sun. But for nocturnal critters it's the moon that matters, affecting everything from lovemaking to lion attacks.
Tungara frogs (Engystomops pustulosus), which live throughout Central and South America, call and mate at night. They usually prefer to be out and about when it's really dark, since illumination increases their risk of getting eaten.
But sometimes the mood strikes while the moon is bright. So what's a lovesick frog to do?
Female Tungara frogs have learned to lower their standards. If it's pitch black she'll choose the most attractive male call, no matter the distance. But if the moon is out, and she can't be bothered with a long hike for love, she'll go for the loudest call, indicating a ready male who's right at hand.
Folklore says that coyotes howl at the full moon, but it turns out they're more particular than that.
Coyotes (Canis latrans) use three different types of howls: lone, group and group-yip howling. For the iconic lone howl, the phase of the moon makes no difference.
But, contrary to mythology, the other kinds of howls are more frequent when there's no moonlight all.
The group and group-yip howls are used to lay claim to territory, and so it could be that the reduced visibility of the new moon means coyotes have increased need for territorial defense.
Another explanation could be that under low visibility coyotes prefer to hunt larger prey. Such a strategy would require group hunting and thus increased communication.
Hundreds of species of coral spawn once a year in a mass synchronized event, releasing millions of eggs and countless numbers of sperm into the water a few nights after a full moon.
The timing of spawning varies from species to species and by location. For instance, in Australia’s Great Barrier Reef, more than 100 of the 400-plus species of corals spawn simultaneously over the course of a few nights during spring or early summer.
But how do they coordinate sex on such a massive scale? It turns out that local weather cycles determine the month in which spawning will take place, but the precise night is set by the lunar cycle—which means scientists (and curious tourists) can predict the date of spawning based on the moon.
Shown here is a star coral (Montastraea franksi) releasing egg and sperm bundles. A hungry ruby red brittle star (Ophioderma rubicundum) gathers up the gametes with its arms and creeps back under the coral ledge to consume them in private.
Darwin suggested that humans' innate fear of darkness is an adaptation for avoiding predation by nocturnal predators. And, at least in the case of lions, it seems he was on to something.
Studies of African lions have found that the darker the evening, the more hunting success lions had and the more food they consumed.
But, contrary to what might be expected, that doesn't mean that dark, new-moon nights are when you should avoid going on safari. Humans are actually most likely to be attacked during the first week after full moon, when it's still more than half-full.
That's probably because the first hours of the night are darkest during the week following full moon—the moon rises at least an hour after sunset. That happens to correlate with the part of the evening that humans are usually outdoors and vulnerable. And the lions are hungriest at that time because of their low predation success during full moon nights.
As that study dramatically concludes, then, "The full moon is not dangerous in itself but is instead a portent of the darkness to come."
Larvae of the antlion group of insects (Myrmeleontidae) are sometimes called doodlebugs—a cute little name that belies their bloodthirsty nature.
You may have seen their lairs: small funnel-shaped pits in dry, fine soil. Hidden under the soil at the bottom of each divot, an immature antlion waits for unsuspecting ants and other small insects to fall in. The unfortunate victim usually is impaled on the antlion's sharp mandibles.
Between weather and failed attacks, the larvae have to rebuild their funnels often. And their structure shows a distinct lunar cycle: around full moon the pits are large, while during new moon they are small.
This may be because there's a higher probability for the antlions to catch prey during moonlit nights, which makes building a bigger pit worth the investment.
But interestingly, these construction rhythms are pre-wired regardless of whether the insects can see the moon: Anlion larvae kept in complete darkness in the lab will still stay in sync with the lunar calendar.
They aren't the most famous nocturnal animal for nothing.
Mature Eurasian eagle owls (Bubo bubo) are most active at the moon's two extremes. During full moon nights, this could be because they have to exert more effort to find rodents, which tend to spend more time hidden from view.
Full moons also drive the owls to show off more for potential mates, which as anyone knows is quite exhausting in itself. On full moon nights the owls make more breeding calls, maybe because that's when their sexy white throat feathers can be seen at the greatest distance.
But that doesn't mean the owls get to be slothful for the rest of the lunar cycle. Hunting effort peaks again near new moon, possibly because, even with their sharp owl eyes, the birds have to work harder to spot prey in the dark.
Moonlight increases visibility for nocturnal hunters such as Belize's jaguars—and it also increases the vulnerability of their prey.
In coastal Belize, armadillos (Dasypus novemcinctus) are the cats' primary prey. Though they may look tough, these little guys know they're no match for a hungry jaguar. So the brighter the moon, the less time armadillos spend out of their burrows.
And jaguars have taken note. On dark nights they're most active at locations with lots of armadillo burrows. But when the full moon is out, the jaguars leave: they're seen only two-thirds as often in these areas.