Exploring the strength of ants and silk

Scientists have discovered two new examples of how strength is a virtue in the world of insects and arachnids.

One team X-rayed ants to better understand how they are able to lift and drag weights many times their own, while the other took an even more in-depth look at a unique Australian spider’s silk.

In the first study, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) in Japan and Sorbonne University in Paris examined the hypothesis that loss of flight in worker ants is directly connected to the evolution of greater strength.

“Worker ants evolved from flying insects,” says OIST’s Evan Economo. “We’ve always assumed that losing flight helped to optimise their bodies for working on the ground, but we have much to learn about how this is achieved.”

In flying insects, wing muscles occupy as much as half of the thorax – the central unit of the body. Once the constraints of flight are removed, the researchers surmised, greater space would allow the remaining muscles to expand and reorganise.

They scanned the anatomy of two distantly related ant species, including the wingless workers and the flying queens, then mapped the different muscles, modelled them in 3D, and compared the findings with those from a range of other ants and wingless insects.

“Within the worker ant’s thorax, everything is integrated beautifully in a tiny space,” said lead researcher Christian Peeters from the Sorbonne, who passed away just before their paper’s publication in the journal Frontiers in Zoology.

“The three muscle groups have all expanded in volume, giving the worker ants more strength and power. There has also been a change in the geometry of the neck muscles, which support and move the head. And the internal attachment of muscles has been modified.”

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The basket-web spider with its unique lobster pot web. Credit: Mark Elgar, the University of Melbourne

In the second study, researchers in Australia and Germany collaborated with the Australian Nuclear Science and Technology Organisation to study the unusual Australian basket-web spider, which weaves a lobster pot web to protect its eggs and trap prey.

Its silk is uniquely rigid and so robust that the web doesn’t need help from surrounding vegetation to maintain its structure.

Analysis using the Australian Synchrotron showed that the silk is in fact similar to that which many species of spider use to wrap around their eggs to protect them from the elements and enemies.

“Our discovery may provide insights into the evolution of foraging webs,” says Mark Elgar, from Australia’s University of Melbourne.

“It is widely thought that silk foraging webs, including the magnificent orb-webs, evolved from the habit of producing silk to protect egg cases. Perhaps the basket-web is an extension of the protective egg case and represents a rare contemporary example of an evolutionary ancestral process.”

Thomas Scheibel from Germany’s University of Bayreuth says the rigidity of the silk appears to come from a synergistic arrangement of microfibres and submicron fibres.

“Nature has created a complex structure that, at first glance, resembles industrially produced composites,” he says. “Further investigations have, however, shown that they are chemically different components and their respective properties together result in the thread’s extreme elasticity and toughness, thus creating a high degree of robustness.”

While more work needs to be done to understand the silk’s molecular details, Scheibel said sees potential interest in a new genetic material that can be produced in a scalable manner.

The findings are published in Scientific Reports.

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