6. One of the most remarkable of nature's living clocks belongs to the fiddler crab, that familiar beach-dweller with the overgrown claw. Biologists have long known that the crab's shell is darkest during the day, grows pale in late afternoon, then begins to darken again at daybreak. This daytime darkening is valuable for protection against enemies and sunlight, and for many years it was thought to be a simple response by the crab to the sun-just as if we were to get a tan during the day and lose it at night.

7. But when an enterprising scientist placed a fiddler crab in darkness, he was amazed to find that the color of the crab's shell kept ticking off the time with the same accuracy.

8. Yet another startling fact was revealed: the crab's shell reached the darkest color about 50 minutes later each day. There was a second clock inside the crab, for the tides also occur 50 minutes later from day to day. Moreover, even when the crabs were taken from the beach and put back in the dark, they continued their tidal rhythm. More research disclosed that a crab from Cape Cod, Massachusetts, reached its darkest color four hours earlier than the one taken from a beach on a neighboring island. The tides on the nearby island were found to be exactly four hours later than the Cape Cod tides.

9. Ants don't carry calendars around with them any more than fiddler crabs possess real wrist watches. But ants show amazing accuracy as to the day of the year. Each year, an ant nest sends out winged, young queens on mating flights. Hundreds of them may fly out of a single nest in the soil. Last summer, at the crest of my mountain, I watched an ant city prepare to send forth its young queens. At the precise moment that they took wing, a colony of the same species that my wife was watching near the bottom of the mountain, also sent its queen on a wedding flight. There was, of course, no way could the two colonies have checked take-off time with each other.

10. Entomologist Albro T.Gaul once jotted down in his notebook that a particular species of ant in northern Massachusetts began its wedding flight at a certain day and time. He later learned that another entomologist in New Jersey, 260 miles away, observed a wedding flight by the same species of ant, on the same day, and at exactly the same time! This split-second timing is not always the rule. However, most flights take place within a definite period of time.