Scientists shaved leaf-cutter ants to uncover how they cut such perfect portions

Leaf-cutter ants need tiny neck hairs to be able to accurately cut leaves, an interesting new German study has shown.

The research involved a laboratory film, a species of American leaf-cutter ant named Atta sexdens and a tiny ‘shaving kit’.

The research has been published in the Journal of Experimental Biology.

Leaf-cutter ants perfectly cut leaves, flowers, and grasses with their mouths to feed to a fungal ‘garden’ which they cultivate year-round.

“Colonies of social insects collect vast quantities of resources. A leaf-cutting ant colony can harvest up to 300kg of fresh plant matter per year, comparable to the yield of a medium-size herbivore,” the researchers write in their new paper.

“At the beginning of a foraging bout, grass-cutting ants cut smaller fragments and return faster to the nest for nestmate recruitment, compared with workers from an established foraging column.

“Although such behaviour leads to an initial suboptimal resource intake for individuals, it was argued that it increases total resource intake at the colony level, because a shortened foraging time enables faster information transfer about discovered food sources.”

But how do these highly-skilled ants know how and when to cut to make the beautiful half heart-shaped cuts (and either big or small) that are then brought back to the nest?

The researchers started by letting the ants start cutting laboratory film rubbed with crushed bramble leaves or rose oil to make them appealing.

Then, once the ants were happily cutting away at the film, the researchers did a bait and switch, and put a piece of paper with a small head-shaped cut out in between the body of the ant and the film they were chewing.

This meant that the ants couldn’t orientate themselves by contact with the leaf’s edge on their hind legs. This might seem like a tricky spot to be in for a little ant, but they could still finish cutting their fragment.

“Ants were able to cut fragments even when contact of all six legs with the edge was prevented, indicating the use of additional sensory information,” the researchers write.

It’s worth noting though that the cut outs made this way were smaller, but the fact they could finish cutting them at all shows that something else was going on.

This is where the shaving (or ablation) came in.

The team carefully shaved the neck hair of about 80 ants by using a broken off glass capillary mounted on a vibrating piezo crystal – basically they made miniature electric razors.

The teeny tiny hairs on the back of the ants neck that were shaved. Credit: Journal of Experimental Biology

The team found that when the shaved ants still had access to the edge of the leaf, they could cut a half heart no problem.

But when the shaved ants didn’t have access to the leaf edge, they were lost completely. They started to produce randomly shaped fragments, completely unlike the heart-shaped pieces the researchers were used to.

“As long as ants have contact with the leaf edge, sensory feedback from the leaf edge is used to control the cutting trajectory, irrespective of the sensory information provided by head movements,” the team write.

“When workers have no contact with the leaf edge, they can continue to keep control over their cutting trajectory by using information provided by the neck’s [hair or] mechanoreceptors. “When information from both feedback mechanisms is completely excluded, workers lose control over the cutting trajectory.”

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