Moving at speeds thousands of times faster than the blink of an eye, the spring-loaded jaws of a trapjaw ant surprisingly capture the insect’s prey and can also launch the ant into the air if it aims its chompers at the ground. Now scientists have revealed how the ant’s jaws can be closed with blisters without being crushed by the force.
In a new study, published Thursday (July 21) in the Journal of Experimental Biology (opens in a new tab)a team of biologists and engineers studied a species of jawed ant called Odontomachus brunneus, native to parts of the United States, Central America and the West Indies. To build up power for their lightning-quick bites, the ants first spread their jaws apart, forming a 180-degree angle, and “buckle” them against locks inside their heads. Enormous muscles, attached to each jaw by a tendon-like cord, pull the jaws into place and flex to build up a store of elastic energy; this bending is so extreme that it distorts the sides of the ant’s head, causing them to bend inward, the team found. When the ant strikes, the jaws lock and the stored energy is released at once, crushing the jaws together.
The researchers examined this spring-loaded mechanism in fine detail, but the project’s engineers wondered how the system could work without generating too much friction. Friction would not only slow the jaws down, but would also generate destructive wear at each jaw’s point of rotation. Using mathematical modelling, they finally found an answer to how trapjaw ants avoid this problem.
“This is the part that engineers are incredibly excited about,” in part because the discovery could pave the way for the construction of tiny robots whose parts can rotate with unmatched speed and precision, says Sheila Patek, the Hehmeyer Professor of Biology at Duke University in Durham, North Carolina. and the study’s senior author, told LiveScience.
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An almost frictionless, spring-loaded system
To study the incredible jaws of O. brunneus, Patek and her colleagues collected ants from a colony found in the scrub forest near Lake Placid, Florida. Back in the lab, the team dissected some of the ants and took detailed measurements and micro-CT scans of their body parts, especially the jaws and muscles and the exoskeleton of the head. They later plugged these measurements into their mathematical models of the ants’ movements.
In addition, the team placed some ants in front of a high-speed camera that took footage at a whopping 300,000 frames per second. (Video is typically shot at 24 to 30 frames per second, for comparison.) These videos revealed that as the ants prepared to strike, the exoskeleton covering their heads underwent significant compression, shortening by about 3%, longitudinally, and growing about 6 % thinner around the middle. This compression took place over several seconds, which feels slow compared to the ant’s quick bite, Patek said.
When the ants were released from the locks, the jaws swung through a perfect arc, reaching top speed around the 65 degree mark before slowing down. At its fastest, the tip of the ant’s jaws traveled about 120 mph (195 km/h) through the air.
This ultrafast movement unfolded smoothly and precisely thanks to multiple forces acting on the jaws simultaneously, the team determined.
First, when the ant’s head bounced back to its normal shape, it threw the tip of each jaw into space. Meanwhile, the large muscles inside the ant’s head relaxed and stopped stretching the tendon-like cords to which they were attached. As each string returned to its normal length—think of a stretched rubber band that suddenly came undone—it jerked at the end of the jaw that sits inside the ant’s head. It is this simultaneous push and pull that sent the ant’s jaws flying towards each other.
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A similar principle applies when you spin a bottle on a flat surface; the twisting motion required to spin the bottle involves pushing one end of the bottle forward while pulling the other end backward. Similarly, when ballerinas perform pirouettes with the support of a partner, the partner will push one of her hips forward and pull the other back to initiate the swing. However, the best analogy for the trap jaw ant’s lower jaw movement may be stick juggling, a circus art in which performers use two sticks to twirl a baton in the air.
The baton encounters little friction as it spins through the air, and based on their mathematical models, the study authors believe that the mandibles of a jaw ant are similarly unrestricted. At first, the researchers thought that each jaw could rotate around a pin joint, similar to a door on a hinge, but they decided that such a structure would introduce too much resistance. Instead, they found that the jaws rotate around a far less rigid joint structure that requires little reinforcement in the ant’s head.
“The dual spring mechanism drastically reduces reaction forces and friction at this joint, so the joint does not need much reinforcement to hold the mandible in place,” study co-author Gregory Sutton, a research fellow at the Royal Society University. University of Lincoln in England, told Live Science in an email. The lack of friction in this system may explain how trapjaw ants can strike again and again without ever harming themselves, the authors concluded.
The authors believe that all trapjaw ants i Odontomachus genus uses the same spring-loaded mechanism to bite, but jawed ants in other genera may use a slightly different strategy, Patek said. That said, Patek suspects that the mechanism they discovered may well be used by other arthropods, meaning insects, spiders and crustaceans.
For example, mantis shrimpknown to throw 50 mph (80 km/h) punches, likely deform their exoskeletons and use superstretchy tendons to build up force with each punch—although such a mechanism has yet to be identified in the shrimp.
“We’re starting to realize that this is going to be the rule of thumb for these super-fast arthropods,” Patek said.
Originally published on Live Science.