Crocodiles are armour-plated torpedoes. Their gnarly heads are all bone with no protruding ears or chubby cheeks. They are so strong that when one five-foot chap, whose mouth was safely shut with tape prior to being transported, slammed my ankle with his head, it felt like being hit with a heavy wooden mallet. I was in excruciating pain, and hobbled for a week nursing a swollen and painful ankle.
Crocodile rivals bludgeon with their heads. They turn their heads away from each other, and whack sideways with force. There’s nothing delicate about these head-banging brawls.
For years at the Croc Bank, we knocked on crocs’ snouts to make them back off. If large ones were intent on chasing us, especially when we were collecting eggs from nests, it took more than mere rapping to stop fiercely protective mother crocs in their tracks.
Then, in November 2012, I read a report by Duncan Leitch and Kenneth Catania of Vanderbilt University, Tennessee, that said bone-plated croc heads were 10 times more sensitive than our fingertips. My eyes widened in amazement.
Every scale of a croc’s body is dotted with tiny pores. For decades, scientists questioned whether they were sensors for detecting changes in water pressure and salinity, underwater prey, magnetic fields, or electricity. Or, did they serve a more prosaic function like secreting oils?
They were formerly called follicle pores, but now they have an impressive name, Integumentary Sense Organs, ISOs for short. Leitch and Catania discovered ISOs were supremely sensitive touch sensors. Just below these pores are quivering raw nerve endings. A vast network of such nerves carries sensations from the face to the brain. To test the sensitivity of the ISOs, the neuroscientists used von Frey filaments, fine hair-like nylon strands.
“We closed our eyes and tried to tickle each other with [the filaments] on our fingertips, and neither of us could even feel it,” Leitch said in an interview to National Geographic News. But crocs could feel it. “My professor [Catania] and I didn't believe at first that they could be that reactive.”
Why do crocs need to be so responsive? When the animals are in the water, ISOs detect the direction of water ripples caused by swimming prey even in total darkness. Additionally, ISOs inside crocs’ mouths are also taste sensors, determining if that bobbing thing in the water was a rubber duck or a real one. Scientists haven’t figured out what functions the numerous pores in different parts of the body serve. Their most amazing purpose is sensing bite pressure.
A full-grown salt water crocodile can slam its mouth shut with a bite force of 3,700 pounds per square inch, the most powerful in the animal kingdom. Come hatching time, those same jaws tenderly squeeze eggs to help babies emerge.
What prevents crocs from using their maximum bite force on an egg? For decades, Rom speculated every tooth socket must have pressure sensors. Now, we know those pressure sensors are ISOs, densely packed around the teeth and inside the mouth. ISOs provide delicate sensitivity to crocs’ bony toughness.
In the wake of these findings, the Croc Bank faces a challenge: How to control crocs with a soft, yet firm, hand? Rapping their sensitive snouts seems horrendous, and touching their chins is just as bad. The staff tried rectangular shields of stiff netting, but crocs’ teeth snagged on them. Lightweight plywood guards are set to be the next experiment, but it already looks unwieldy. Ideally, it would take a futuristic invention like force fields to deter crocs without touching them.
But how do crocs tolerate pain caused by head-bashing contests? Did the croc that whacked its ISO-rich snout against my ankle suffer more than I?
Or, are crocs’ heads like our palms that are capable of tenderly stroking a baby to sleep and delivering a stinging slap?