Many people have seen crabs scurrying along the sand and taking cover in their well-kept burrows, but these animals are still largely a mystery to even the most dedicated beach bums. Marine biologists who study crabs are working to shed light on the fascinating lives of these crafty crustaceans. Here is just a sampling of their latest findings:

• Crabs are capable of learning and remembering information, just like other animals. A recent article in the Journal of Neuroscience concluded, “Experiments with … crabs demonstrate their remarkable capacity to learn and memorize visual features.”¹ Crabs learn to avoid food that makes them ill—this discovery is groundbreaking because it demonstrates that crabs are capable of learning from their mistakes and retaining that information so that they don’t make the same mistake again in the future.²

• Crabs adapt to changing cues in their environment. In one experiment, researchers moved a screen over the water above the crabs to mimick the cues of a seagull or other predator passing overhead. At first, the crabs ran into to their burrows, but after they were “tricked” a few times, the crabs learned that the darkness didn’t correspond with danger, and they no longer fled. This research proved that crabs’ reactions are not merely rigid, unconscious reflexes—they react to different stimuli based on what they have learned and remembered from their past experiences.³

• Crabs have sensitive hairs on their bodies that register vibrations caused by sound waves much like the hairs in our ears sense sound vibrations. Crabs use the drumming of their claws to make sounds to attract mates and warn other crabs about predators—according to a study published in the Journal of Comparative Physiology, “[Crabs] detect acoustic stimuli …, socially interact in acoustic ‘choruses,’ and probably use ‘calls’ to attract mates.”⁴

• Bromeliad crabs, who live in small pools of water in bromeliad flowers, provide loving care for their young, according to research conducted by marine biologists. The mother crabs continue to feed and tend to their babies for several months after they are born. They work hard to keep their homes clean and comfortable for their young. S. Blair Hedges, a biologist who has researched the manner in which crabs care for their offspring, says, “The mother crab manipulates water quality by removing debris, by circulating the water to add oxygen to it, and by carrying empty snail shells into the water to buffer the pH levels and add calcium.”⁵

• Crabs are good neighbors who look out for one another: Scientists found that if a male Australian fiddler crab’s burrow is being invaded by a male intruder looking to take over the burrow, his male neighbor will leave his own burrow to help fight off the intruder. Scientists also found that the two neighboring crabs will never fight each other. This study indicates that crabs recognize the benefits of having a good neighbor. The study also found that crabs appear to use “judicious decision making” to decide when they should risk their own safety to help their neighbor.⁶

Read more.

¹D. Tomsic, M. Beron de Astrada, and J. Sztarker, “Identification of Individual Neurons Reflecting Short- and Long-Term Visual Memory in an Arthropodo,” Journal of Neuroscience 17 Sep. 2003.
²K. Wight, L. Francis and D. Eldridge, “Food Aversion Learning by the Hermit Crab Pagurus granosimanus,” The Biological Bulletin.
³Valerie Depraetere, “Water on the Brain,” Nature 3 Nov. 2000.
⁴Arthur Popper, Michael Salmon, and Kenneth Horch, “Acoustic Detection and Communication by Decapod Crustaceans,” Journal of Comparative Physiology 187 (2001): 83-9.
⁵“Tiny Jamaican Tree Crab Made Big and Fast Evolutionary Leap, Scientists Discover,” Penn State University, 27 May 1998.
⁶“Crabs Cooperate to Defend Their Territories,” Compassion in World Farming Trust, 15 Aug. 2004.

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