You're familiar with the human circadian clock: the twenty‑four hour cycle of light and dark, we sleep, we wake, we release hormones, our body temperature changes.

But did you know there's a type of marine worm that, along with following a circadian clock, follows a lunar clock? Its spawning is influenced by the thirty‑day moon cycle. And bees also have unusual biological clocks. They change their clocks depending on their job in the hive.

Nurse bees forgo the circadian cycle when they care for larvae night and day, while foragers follow regular circadian cycles. If the bees switch roles, the nurse‑turned‑forager will start following a circadian clock again, and the forager‑turned‑nurse will stop.

Cavefish and Reindeer

It's not just bugs who have different circadian cycles. Arctic reindeer, since they live in perpetual daylight in summer and perpetual darkness in winter, have lost their circadian rhythm.

There's also the forty‑seven hour cycle of the Somalian cavefish. They haven't seen light in over a million years, so their clocks no longer respond to a twenty‑four hour cycle. Scientists think they may be responding to cyclical changes in the caves.

It seems like there might be an easy to predict relationship between location and circadian rhythm, but there are Mexican cavefish whose circadian clocks are unusual. Their circadian clocks seem jammed in perpetual daylight.

Imagine how much your life would change if your circadian clock was different.