The Sharp Science of Animal Strikes
Chance may favor the prepared, but nature favors the zippy. A group of scientists have studied how animals great and small manage to strike and puncture their often well-protected prey, and they reported their findings in the journal Interface Focus.
The action of striking and piercing an object or another creature is more complex than it looks, and each pouncing animal has its own technique. Snakes lunge and bite to inject venom, while zebra mantis shrimp (which are not zebras, mantises, or shrimp) spear their prey with a harpoon-like claw. For trapjaw ants, the action is all in the mandibles, which can slam shut at up to 145 miles per hour. Jellyfish and the Portuguese man-of-war strike at a microscopic level using itsy-bitsy stinging missile-launchers called nematocysts.
These attack styles may look very different, but study co-author Phillip Anderson of the University of Illinois suspected that the underlying mechanics had a lot in common. "What's really cool from the evolutionary point of view is that it's not often that you have the ability to look at biomechanical systems across such a wide range of animals that are all trying to achieve a similar performance," he said in a press statement. But instead of studying the animals themselves, Anderson picked up a crossbow and aimed it at ballistic gelatin.
Forensic experts generally use ballistic gelatin to test the action of various guns. The squishy, resilient gelatin is a decent stand-in for human and other animal tissue. But Anderson and his colleagues decided it would be equally useful to test punctures made by a bolt. They fired a single bolt into a 4-inch cube of gelatin again and again, adding weight to the bolt between each test.
Video: Philip Anderson
At certain weights, the bolt pierced with no trouble. At others, it made a partial puncture before the gelatin spit it back out. "The target material builds up elastic energy as it deforms,” Anderson said. “At a certain point the elastic energy in the material causes it to push back against the arrow. If the elastic energy is large enough, it can eject the arrow.”
Because the researchers knew the velocity and mass of each test run, they were able to calculate the effects of varying amounts of kinetic energy on the gelatin. They found that the more kinetic energy the bolt had, the more successful it was at puncturing the gelatin. But heavier bolts weren’t better off: It was velocity, not mass, that increased the bolt’s kinetic energy.
"This means that one potential way for small animals to puncture and get through tough materials, even with a low mass, is to increase their speed," Anderson said. "And if you look across animals that puncture, it appears that the smaller ones tend to be faster."
Check out this cool infographic about their findings for more details:
Image credit: Julie McMahon