It also helps protect them against infection by the disease-causing fungus Metarhizium anisopliae, which might otherwise spread rapidly through their dense colonies.

A well-known leaf-cutter ant grows its own armor using biominerals, a protective power previously unknown in the insect world, scientists have discovered in research published Tuesday showing this makes the ants almost invincible in battle.

Biomineral armor is seen in the natural world in crustaceans such as lobsters, as well as other marine animals (sea urchins’ spines contain calcium carbonate, for example), but has not previously been found in insects.

Researchers stumbled upon the discovery while investigating the relationship between ant species that grow fungi Acromyrmex echinatior and antibiotic-producing bacteria that help protect their crops.

They noted that the largest worker ants, known as majors, have a “whitish granular coating” on the surface of their bodies, according to co-author Cameron Currie, a professor of bacteriology at the University of Wisconsin-Madison.

This brochure image released on November 23, 2020 by the Smithsonian Institution shows a white-coated Acromyrmex echiniator ant. | Author of the photo:
AFP

He said that Hongjie Li, the lead author of the report published in Communications from nature, “He was fascinated with crystals” and discovered that it was a biomineral layer that develops as ants mature, increasing the hardness of their exoskeleton and covering almost the entire body.

While researchers are not sure why ants have this unusual armor, Currie said AFP they suspect that it has a lot to do with the soldier ants of another species of ants that grow mushrooms, Atta cephalotes. The two species will often participate in territorial “ant wars,” which the researchers simulated in laboratory battles. “When Major League Acro is without their armor, Atta’s soldiers quickly cut them to pieces, literally,” Currie said. “When they have their armor, they actually go from almost always losing battles to almost always winning.”

The authors found that the benefits of a biomineralized exoskeleton go beyond giving workers an advantage in ant wars.

Their studies suggest that it also helps protect them against infection from the fungus that causes the disease. Metarhizium anisopliae, which could otherwise spread rapidly through its dense colonies.

Rare like sea urchin teeth

Ants are believed to have started mushroom subsistence farming around 60 million years ago in South America.

About 20 million years ago the practice became more “industrialized”, with the appearance of species of leaf-cutter ants such as Acromyrmex echinatior Y Atta cephalotes They live in large, complex colonies and harvest fresh vegetation that they use to grow their mushrooms.

Acromyrmex echinatior Colonies can form with hundreds of thousands of large and small worker ants. “The big ones cut and transport leaves, in addition to participating in wars and battles with other ants,” Currie said. “The little ones do the gardening.”

Atta’s colonies are larger, made up of perhaps millions of ants, with up to seven different sizes of workers, including soldiers for “ant defense and warfare,” Currie said.

the Acromyrmex echinatior The armor is made of calcite with a high magnesium content, the researchers found. This is a rarer form of biomineralization in which increasing magnesium hardness is believed to help them grind up limestone.

Since the armor was just found in a relatively well-studied ant species, the researchers said this type of biomineral protection might be more widespread in the insect world.

But Currie said it’s likely the calcite biominerals most commonly found in marine animals like lobsters, rather than the high-magnesium calcite from the armor of ants and sea urchin teeth. “These ants are quite special in many ways,” he added.

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