Leaf cutter ant jaws have the durability of stainless steel knives

“Small but terrible” is what aptly describes leaf cutter ants. Their metal teeth can pierce hard materials like wood or even skin. What causes these arthropods to acquire their edge has been explained by a new study published in the review Scientific reports.

Leaf cutter ants (Atta cephalotes) Usually consists of foraging columns made up of hundreds or thousands of ants carrying small pieces of leaves. They cut pieces of leaves with their jaws and carry the fragments to an underground nest.

Scientists discovered under a microscope a web of zinc atoms woven into the biological structure of ants’ jaws, which explains why they have sharp teeth with “the durability of a set of stainless steel knives,” said authors.

Zinc laced in their teeth allows the edge to form a fine point, keeping them sharp for a long time.

“The little animals that had this material, their muscles are microscopic compared to ours,†said lead author Robert Schofield, also a biophysicist at the University of Oregon.

The biting trick of arthropods

Compared to a human jawbone, arthropods such as the ant bite trick are a “remarkable feat.” Schofield noted that “metal-mouthed arthropods take advantage of their sharp choppers to precisely apply the right amount of cutting force to slice leaves or hide.”

Although the team of researchers know that ants’ teeth contain a lot of zinc, how the metal atoms have been arranged and how it helps ants bite remains unknown. Using an ion beam microscope, the team examined the material makeup of leaf-cutting ants’ teeth before and after biting to calculate their hardness, sharpness, and durability.

“Ants don’t rely much on the mandibles to process food,” said Cristian Klunk, an environmentalist at the Federal University of Parana, Brazil, who was not involved in the study. “But they use them for just about every other job, from defense to home improvement, so they have to keep them in top shape.”

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How an ant’s jaw differs from ours

Human teeth are covered with a layer of enamel, a material rich in calcium which is the hardest substance in the human body. Looking at an enamel under an electron microscope would show you calcium and phosphate molecules forming a large crystalline matrix around the carbon, hydrogen, and oxygen atoms. These crystals are what make teeth strong, but keep them from being razor sharp at the same time.

This material is not far from what ants have. The ant’s mandible is covered with a smooth mixture of crisscrossed proteins of zinc which is the equivalent of human tooth enamel for resistance, also known as “heavy element biomaterial†(HEB). However, zinc does not form polyhedral crystals; instead, it remains evenly distributed throughout the protein mixture, allowing teeth to have sharp edges.

Metal reinforcements aren’t limited to ant teeth either. Other invertebrates also weave zinc or a similar metal, manganese, in their jaws. In fact, adding zinc or manganese to their exoskeleton reduces the force required to pierce or cut hard materials by 60%.

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