Leaf cutter ant, first insect found with biomineral body armor

A well-known leaf-cutter ant cultivates its own body armor using biominerals, a protective power hitherto unknown to the insect world, scientists found in research published Tuesday showing that it makes ants almost unbeatable in the world. fight.

Biomineral armor is found in the natural world in crustaceans like lobsters as well as in other marine animals – sea urchin spines contain calcium carbonate, for example – but it has never been found in insects.

The researchers stumbled upon this discovery while studying the relationship between the fungal-growing ant species Acromyrmex echinatior and the antibiotic-producing bacteria that help them protect their crops.

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

He said Hongjie Li, the lead author of the report published in Nature’s communications, “became fascinated with crystals” and discovered that it was a biomineral layer that developed 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 told AFP they suspected it had a lot to do with the soldier ants of another species of mushroom ants, Atta cephalotes. .

The two species will often engage in territorial “ant wars”, which the researchers simulated in laboratory battles.

“When the Acro majors are unarmoured, the Atta soldiers quickly cut them to pieces, literally,” Currie said.

“When they have their armor on, 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 edge in ant wars.

Their studies suggest that it also helps them protect them from infection with the disease-causing fungus Metarhizium anisopliae, which could otherwise spread rapidly through their dense colonies.

Rare like sea urchin teeth

It is believed that ants began subsistence farming of mushrooms around 60 million years ago in South America.

About 20 million years ago, the practice became more ‘industrialized’, with the emergence of leaf-cutter ant species such as Acromyrmex echinatior and Atta cephalotes living in large, complex colonies and harvesting fresh vegetation that ‘they use to grow their mushroom.

Colonies of Acromyrmex echinatior can be formed with hundreds of thousands of large and small worker ants.

“The bigger ones do the cutting and hauling of the leaves, as well as engaging in wars and battles with other ants,” Currie said.

“The little ones are gardening.”

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

Acromyrmex echinatior armor is made from high-magnesium calcite, the researchers found.

This is a rarer form of biomineralization where it is believed that increasing the hardness of magnesium helps them crush lime.

Since the armor was only just found on a relatively well-studied species of ants, the researchers said this type of biomineral protection may be more prevalent in the insect world.

But Currie said it was likely the calcite biomaterials more commonly found in marine animals like lobsters, rather than the high-magnesium calcite from ant armor and sea urchin teeth.

“These ants are quite special in a lot of ways,” he added.

© 2020 AFP