How do trap-jaw ants prevent blowing their heads off? •


Trap-jawed ants (Odontomachus brunneus) are predatory insects with exceptional jaws. They open their jaws 180oh and lock them until they need to close them. A snap, when it occurs, takes only a few microseconds and involves considerable force. In fact, this ant’s jaws are among the fastest appendages in the animal kingdom.

Ants use these jaws to stun or kill their prey primarily, but may also release the snap near the surface of the ground. This action ends up propelling the ant into the air, either as a kind of “leap” to facilitate locomotion, or to get the ant out of a delicate situation.

When not being used to kill prey or jump to safety, the ant’s jaws can be used with extreme delicacy to greet other ants or to manipulate small pieces of food. Impressed by the way trap-jaw ants use their jaws for delicate maneuvers and savage thrusts, a team led by Duke University’s Sheila Patek 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 United States, Central America and the West Indies. Patek and his colleagues collected specimens from a colony they found in scrubland near Lake Placid, Florida. They dissected some of the ants and took detailed measurements and micro-scans of the head and jaws. The experts used these measurements to model the ant’s movements and understand what allows it to release its jaws so forcefully and quickly.

Study co-author Chi-Yun Kuo gently stared the ants in front of a high-speed camera and filmed their jaw movements at 300,000 frames per second to capture the lightning-fast maneuver as the insects crushed their mandibles together.

After release, each mandible swung in a perfect arc through the first 65oh before decelerating and coming to a stop. “When we played the videos in slow motion, their strikes were spectacularly accurate,” Patek said.

The researchers found that the ants used two distinct spring mechanisms to accomplish their powerful jaw snaps. First, the muscles spread the jaws so that there is a 180oh angle between them. In doing so, they distort the sides of the ant’s head somewhat, making it slightly shorter (3.2%) and narrower (6%) in the middle. As the exoskeleton flexes inward, it stores elastic potential energy that can be used when the jaws are released.

Secondly, huge muscles attach to each jaw by means of elastic elastic tendons. Thus, torque is developed by having stored elastic energy in two different sites on each mandible. When the jaws are released, the head capsule returns to its normal shape and this pushes part of the mandible forward, away from the body. At the same time, the elastic tendons pull the inner edge of each jaw towards the body. This causes the jaws to swing in a perfect arc and reach a top speed of around 120 mph (195 km/h). The movement is equivalent to spinning at 470,000 rpm. The researchers call this system a “dual spring-force torque,” ​​because two springs deliver energy to two different places at the same time, on each mandible.

By calculating the amount of energy released when the insects released their smashing mandibles, the team found that the energy stored during the deformation of the head’s exoskeleton was enough to drive the mandibles through 33oh of perfect rotation. Energy stored in the elastic tendon connecting the mandible to the huge adductor muscle inside the head (comprising 14% of the ant’s body mass) powered the remaining 32 masses.oh of the bow.

Researchers wondered how this spring system could work without generating excessive friction, which would slow jaw movement and cause joint wear. Using dynamic modeling, they found that the double-spring torques reduce the need for joint stresses and that the ants had a much less rigid joint structure than expected. This system reduces friction, which is essential if the ant has to close its jaws repeatedly.

Trap-jawed ants thus use a mechanism that allows them to coordinate opposing forces resulting in the perfect rotation of the mandible. Since no stress is exerted on the fragile joint around which the mandible pivots, there is no harm to the ant itself, no matter 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 adopted by engineers.

“The principles can be integrated with microrobotics to improve the multifunctionality, precision and longevity of ultrafast systems,” they state.

More details on the study can be found at:

By Alison Bosman, Personal editor


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