Trap jaw ants (Odontomachus brunneus) are predatory insects with exceptional jaws. They open their jaws 180o and close them there until they have to close them. An instant, when it happens, takes only microseconds and involves considerable force. In fact, this ant’s jaws are among the fastest moving appendages in the animal kingdom.
Ants use these jaws to stun or kill prey mostly, but they can also release the button near the soil surface. This action ends up propelling the ant into the air, either as a sort of “jump” to aid locomotion or to get the ant out of a sticky situation.
When not being used to kill prey or jump to safety, the ant’s jaws can be used very delicately to greet other ants or to handle small pieces of food. Impressed by the way trapjaw ants use their jaws for both delicate maneuvers and savage strikes, a team led by Sheila Patek at Duke University set out to investigate how these jaws work. The fascinating results of the study are published in the Journal of Experimental Biology.
The species is native to the southern parts of the US, Central America and the West Indies. Patek and his colleagues collected specimens from a colony they found in thickets near Lake Placid, Florida. They dissected some of the ants and took detailed measurements and micro-CT scans of the heads and jaws. The experts used these measurements to model the ants’ movements and understand what allows them to release their jaws with such force and speed.
Study co-author Chi-Yun Kuo gently secured the ants in front of a high-speed camera and filmed their jaw movements at 300,000 frames per second to capture the lightning-quick maneuver as the insects their jaws clashed.
After release, each jaw rotated in a perfect arc for the first 65o before decelerating and coming to rest. “When we played back the videos in slow motion, his shots were spectacularly accurate,” Patek said.
The researchers found that the ants used two separate spring mechanisms to achieve their powerful jaw sockets. First, the muscles pull the jaws so that there is an angle of 180o between them. In doing so, they slightly deform the sides of the ant’s head, making it slightly shorter (3.2 percent) and narrower (6 percent) in the middle. As the exoskeleton deforms inward, it stores elastic potential energy that can be used when the jaws are released.
Second, the huge muscles are attached to each jaw by elastic elastic tendons. Thus, the torque is developed by having stored elastic energy in two different places in each jaw. When the jaws are released, the head capsule returns to its normal shape and this pushes part of the jaw forward, away from the body. At the same time, elastic tendons pull the inner edge of each jaw toward the body. This causes the jaws to swing outwards in a perfect arc and achieve a top speed of about 120 mph (195 km/h). The movement is equivalent to spinning at 470,000 rpm. The researchers call this system a “dual spring force couple,” because two springs provide energy in two different places at once, in each jaw.
By calculating the amount of energy released as the insects released their crushing jaws, the team discovered that the energy stored when the head exoskeleton was deformed was enough to drive the jaws into a perfect 33o rotation. Energy stored in the elastic tendon that connects the jaw to the huge adductor muscle inside the head (which make up 14 percent of the ant’s body mass) powered the remaining 32o of the bow.
The researchers were puzzled as to how this spring system could work without generating excessive friction, which would delay jaw movements and cause joint wear. Using dynamic modeling, they found that dual spring force pairs reduce the need for joint constraints and that the ants had a much less rigid joint structure than they expected. This system reduces friction, which is essential if the ant wants to close its jaws repeatedly.
In this way, trap ants use a mechanism that allows them to coordinate the opposing forces that drive the perfect rotation of the jaw. Because no stress is placed on the fragile joint on which the jaw pivots, there is no damage to the ant, regardless of how often it closes its jaws.
Patek suspects that other spring-loaded creatures also use the strategy, and she, Sarah Bergbreiter (Carnegie Mellon University, USA) and Suzanne Cox (Duke University) suggest that the revolutionary design could be embraced by engineers.
“The principles can be incorporated into microrobotics to improve the multifunctionality, accuracy and longevity of ultrafast systems,” they say.
More details of the study can be found at:
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By Alison Bosman, Earth.com Staff Writer