Scientists find leaf-cutter ant grows body armour

An Atta cephalote soldier (R), the largest worker caste within the leaf-cutter ant colonies, extending her mandibles over an Acromyrmex echinatior worker. AFP/Caitlin M. Carlson/University of Wisconsin-Madison

PARIS - A well-known leaf-cutting ant grows its own body armour using biominerals, a protective power previously unknown in the insect world, scientists have discovered.

Biomineral armour is seen 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 not previously been found in insects. 

Researchers stumbled across the discovery while investigating the relationship between the fungus-growing ant species Acromyrmex echinatior and antibiotic-producing bacteria that helps them protect their crops. 

They noticed that the larger worker ants, known as majors, have a "whitish, granular coating" over the surface of their bodies, according to co-author Cameron Currie, professor of Bacteriology at the University of Wisconsin-Madison.   

While researchers do not know for certain why the ants have this unusual armour, Currie told AFP they suspect it has a lot to do with the soldier ants of another species of fungus-growing ants, Atta cephalotes. 

The two species will often engage in territorial "ant wars", which the researchers simulated in lab-based battles.   

"When the Acro majors are without their armour the Atta soldiers quickly cut them into pieces, literally," Currie said.  

"When they have their armour, they actually go from almost always losing the battles to almost always winning."

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

Their studies suggest it also helps protect them against infection from the disease-causing fungus Metarhizium anisopliae, which might otherwise spread quickly through their dense colonies.

The Acromyrmex echinatior armour is made from a high-magnesium calcite, researchers found. 

This is a rarer form of biomineralisation where the increased hardness from the magnesium is thought to help them grind up limestone.

Given that the armour has only just been found on a relatively well-studied ant species, the researchers said this type of biomineral protection could be more widespread in the insect world. 

But Currie said this was likely to be the calcite biominerals found more commonly in marine animals like lobsters, rather than the high-magnesium calcite of the ants' armour and sea urchin teeth.

"These ants are pretty special in many regards," he added.


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