Ants have a sharp bite well above their weight class thanks to the infusion of hard metals such as zinc and manganese into their lower jaws.
New research with an advanced microscope shows that a number of arthropods, such as ants, camel spiders, scorpions and bristle worms, have adapted the use of these hard minerals to give their sharp appendages extra strength when cutting leaves or stinging their prey.
Small creatures with big bites
Usually, small creatures don’t have as much power as larger creatures when it comes to biting, stinging, or cutting. A rough rule of thumb is that a creature 10 times taller than another can exert 100 times as much force if both creatures’ muscles are in equal proportion to their body size,” said Robert Schofield, a physicist at the University of Oregon. .
However, small creatures such as ants, scorpions and spiders still manage to penetrate hard surfaces with stingers or cut through relatively tough leaves. They do this in part thanks to incredibly sharp appendages that can penetrate hard surfaces with considerably less force.
“The trick is that they use sharp tools that focus that much smaller force on a much smaller area and get basically the same pressure,” Schofield says.
But these creatures are not always blessed with a knife sharpener. Schofield and his colleagues wondered how they could maintain a strong level of sharpness, as their canines, stingers or jaws wore out over time with use. For example, in the case of leafcutter ants, the average sharpness of their lower jaws decreases over time, forcing older ants to work twice as hard to cut through the same leaves as younger ants.
“It can be fatal to a small organism that relies on it” [sharpness]’ says Schofield. “The wear and tear, for these tiny organisms, may be enough to determine their longevity.”
New tools to research ant tools
Schofield has always been interested in using physics to better understand biology – he says he could never decide whether to become a biologist or a physicist in his studies. He chose the latter and during his Ph.D. research, he helped invent a microscope that used atomic probe tomography.
In a study recently published in Scientific Reports, Schofield and his colleagues describe how they used this Atomic Force microscope and built miniature testing machines to better understand the mechanics of strong bites and stings. They examined the jaws, stingers, and other tools of leafcutter ants (Atta cephalotes), Nereid worms, (neanthes brandti), scorpions (Hadrurus arizonensis), spiders (Araneus diadematus) and other species.
They found that the tools of many of these creatures contain a lot of zinc and manganese. “It was very bizarre because there was so much,” says Schofield.
For example, the mandibles of ants contain up to 16 percent zinc. The stings of scorpions contained up to 20 percent zinc.
Schofield says these hard materials help the creatures stay sharp enough to cut through leaves or pierce the hard shells of their prey. “These are really strong advantages from an evolutionary standpoint,” he says.
The zinc also stiffens their stingers or jaws – an important factor that helps maintain sharpness under the pressure of cutting and piercing. The researchers calculated the force required to pierce hard materials using stingers containing zinc and manganese and found that it made a huge difference compared to the force a creature would need if its stinger was simply made of other material from the exoskeletons of the creatures. The hardness of ant teeth also increases when zinc is added, their measurements showed. Without zinc, they are about as hard as plastic. Zinc makes their teeth as hard as aluminum.
The researchers also say the canines and stingers they examined represent an entirely new class of structural biomaterials — the other two being the mineralized materials of bones or teeth and the common organic materials like those in fingernails.
Schofield says the team is doing follow-up research to see if some of these creatures can replenish or self-heal the zinc and manganese levels in their mandibles or stings when they break.