Ant jaws snap shut 700 times quicker than a blink of an eye
The engineering of trap-jaw ant mandibles demonstrates a fascinating example of convergent evolution.
“In ways that become wholly apparent only when one’s line of sight is dropped to a millimetre off the ground,” wrote myrmecologists Edward O. Wilson and Bert Holldobler in their 1994 book Journey to the Ants, “ants lie heavily upon the rest of the fauna and flora.”
In research published this week in the Journal of Experimental Biology, the way in which one particular species of ant dominates its own little patch of flora and fauna has finally been made plain. All it required was a microscope, a machine capable of micro-computed tomography (micro-CT), and movie camera equipped with a macro lens able to shoot 50,000 frames per second.
Researchers led by Fredrick Larabee from the Smithsonian National Museum of Natural History set out to determine just how fast one genus of trap-jaw ants can slam shut their jaws. The answer: 80 km/h.
This means that if you happen to be the ant’s natural prey – tiny arthropods known as springtails – you have virtually no chance of getting out of the way in time.
The trap-jaw genus, known as Myrmoteras, is found primarily in Southeast Asia. To achieve the high-speed jaw snap, the ants’ mandibles latch into place at a 280-degree angle – tensed, possessing considerable stored elastic energy.
Slipping the latch releases that energy, causing the jaws to snap shut in half a millisecond – about 700 times faster than it takes a human eye to blink.
The speed of the mandible action is far faster than could be achieved if the ants relied solely on their musculature. The scientists detected notches on the jaws that allowed them to wedge open. A lobe on the back of the ant’s head acting as a trigger; its compression releases the latch.
For Larabee and his colleagues, just having enough Myrmoteras to work with was a significant triumph of expert ant husbandry. The species are difficult to find in the wild and have proven challenging to keep alive in the lab.
Having successfully recorded the speed at which the ants are able to snap, it was perhaps a bittersweet moment to concede they are not, in the end, the fastest-moving insects in nature.
Trap-jaw ants of the Odontomachus genus have jaws that, using a similar mechanism, snap shut at twice the speed. This ability is used for hunting and also to propel the ants backwards as a maneouvre to avoid predators.
The Myrmoteras ants do not seem to use their jaws for similar evasive purposes. "They just need to be faster than the critters they're trying to eat,” Larabee says, “and their jaws are plenty fast for capturing springtails."
Another Smithsonian team discovered in 2016 that a family of South American and New Zealand spiders known as the Mecysmaucheniidae also hunt using a latch-based trap-jaw system to hunt.
Similar systems have been found for other functions in the arthropod world – propelling grasshopper and flea jumps, for instance. Though there are differences in biomechanics – Myrmoteras represents “a completely unique evolution,” Larabee says – the latch-and-release system represents an interesting example of convergent evolution.