In ancient times, sailors on the ocean and far from land were in trouble if they could not see the sun, stars, or any landmark. The method they used was called “dead reckoning.” Today scientists call it “path integration.” The sailors determined how far they had traveled and in what direction to figure out where they were. The farther they traveled, and the more turns made, the less accurate the locating method was.
One of the most common animals along the shore of the ocean is the fiddler crab. The name comes from having one claw vastly oversized reminding you of someone carrying a fiddle. Being about an inch long, they are defenseless against birds and other predators. They survive by ducking into their burrows when they feel threatened.
To locate their burrows, fiddler crabs use “path integration” very successfully. Their burrows are on mud flats, and these small crustaceans feed on organic matter they sift from sediment. Their vision is poor, so once they are three or four body lengths from their burrow they cannot see it. At low tide they come out of the burrow to forage, and they will go as far as 25 body lengths or more away from their burrow. When they are frightened, they make a beeline straight for the burrow. There are no landmarks, no odor trails, and no evidence that they are using magnetism or light to survive in this flat and bland topography. Recent studies have shown they use path integration.
Researchers have found that the crabs measure how far their eight tiny legs have propelled them. The crabs keep a running measurement at all times of where they are in relation to their holes. The crabs avoid error-inducing turns as they forage by holding their bodies in a fixed orientation. Researchers rubbed baby oil on acetate sheets and placed them near the burrows. They filmed the fiddler crabs slipping and skating across the slippery plastic. When they were startled, the crabs ran the number of steps it should have taken to get to their burrows and stopped, but the burrow was not there.
Measuring their step length, counting the steps, and keeping the error-inducing movement to zero is the key to survival for these fascinating creatures. God’s design gives them the ability to survive in a featureless environment by building into their DNA a survival plan that fits the place where they live.
Source: National Wildlife, February/March 2014, page 33.
Picture credits:
Top: http://commons.wikimedia.org/wiki/File:Fiddler_crab.jpg
bottom: http://commons.wikimedia.org/wiki/File:Fiddler_crab_anatomy-en.svg