Biomineral Body Armor Shields Leaf-Cutter Ants in Deathmatches, Says Study

Leaf-cutter ants 'grow' biomineral armor, a distinct edge in ant wars and resisting disease.
Brad Bergan

A popular leaf-cutting ant grows organic body armor with biominerals — a shield-like power previously unknown to students of the insect world, according to a recent study published in the journal Nature Communications.

This previously undiscovered advantage makes leaf-cutting ants practically invincible against other rival ant species.


Leaf-cutting ants use biomineral body armor to shield themselves

In nature, biomineral armor is typically found on crustaceans like lobsters and other marine animals — for example, sea-urchin spines possess calcium carbonate — but no one had seen it in or on insects before.

Researchers collided with this discovery while looking into the relationship between the fungus-growing ant species Acromyrmex echinatior and antibiotic-producing bacteria capable of shielding their crops.

Until they noticed the larger worker ants — called majors — had a "whitish, granular coating" over their body surfaces, according to one study co-author named Cameron Currie — who's a professor of bacteriology at the University of Wisconsin-Madison.

Biomineralized exoskeletons also protect ants from disease

Lead author of the new study Hongjie Li "became fascinated with the crystals" and found a biomineral layer that grows as ants mature, said Currie. This biomineral layer makes ant exoskeletons hard, and covers their whole body.

Researchers still don't know why the leaf-cutting ants have this strange armor, said Currie to AFP. But the team thinks it might be linked to soldier ants of another species of fungus-growing ants, called Atta cephalotes.

These two ants often fight in territorial "ant wars" — which researchers simulated in lab-based deathmatches. "When the Acro majors are without their armor the Atta soldiers quickly cut them into pieces, literally," said Currie. "When they have their armor, they actually go from almost always losing the battles to almost always winning."

The study authors discovered how the benefits of a biomineralized exoskeleton add a substantial advantage in the ant wars. Their studies also show the shield helps insulate the ants from infection via a fungus called Metarhizium anisopliae — a disease-causing organism — which would otherwise spread rapidly through dense ant colonies.

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Biomineral armor could be more widespread in nature

Ants are thought to have begun farming fungus roughly 60 million years ago, in South America. Roughly 20 billion years ago, this process went industrial when ants like the leaf-cutting Acromyrmex echinatior and Atta cephalotes started living in massive, complex colonies — and harvesting fresh vegetation with which they grow their precious fungus.

Hundreds of thousands of large and small worker ants live in leaf-cutter colonies. "The large ones do the cutting and carrying of leaves, as well as engaging in wars and battles with other ants," Currie noted. "The small ones do the gardening."

In light of the sheer volume of this biomineral armor on the leaf-cutter ants, the researchers think it could be more common in the insect world than previously thought. While we probably can't adapt this armor for humans — against the coronavirus crisis or one another — it's still interesting to know why some ants win fights they typically would have poor chances of surviving.

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