Spider, ant, scorpion: firm bite and strong sting thanks to heavy metal

A new study has shown that a mixture of proteins and heavy metals such as zinc and copper makes invertebrate tools particularly hard and robust.

A weaving spider (Phidippus regius) shows her dazzling biting claws.

When they suck blood from a deer, ticks bite hard into the animal’s furry skin. Leaf-cutter ants effortlessly gnaw their way through the thick leaves of tropical plants. With their sting, scorpions inject their venom even into animals many times larger than themselves.

The question of where these sometimes tiny animals get such great power has long fascinated Robert Schofield, a physicist at the University of Oregon in Eugene. He published his answer in a new study published in the journal Scientific Report.

The secret lies in the anatomical structure of the material from which the animals’ tools are made. Scientists discovered some time ago that the biting claws, jaws and spines of some invertebrate species consist largely of heavy metals such as zinc, copper and manganese – in some cases accounting for up to 20 percent of a species’ body weight. So far, however, it has not been possible to clarify how the metals are related to the long-lived proteins that have also been found in these body parts of invertebrates.

Gallery: Early macro images of insects& Spiders

In a molecular analysis of heavy metals and proteins, Robert Schofield and his colleagues found that individual metal atoms are interwoven with proteins. The result is strong, resilient composites that scientists have christened heavy-element biomaterials.

"It’s really cool how durable adding these metals makes the tools," says Stephanie Crofts, a biologist at the College of the Holy Cross in Worcester, Massachusetts, who was not involved in the study. "Research has shown that this buildup of material occurs in a whole range of organisms – far more than we had thought."

Heavy element biomaterials: Better than biominerals

A process in the animal kingdom that naturally creates insensitive materials is biomineralization, in which larger mineral crystals are enclosed by the proteins in an animal’s body. This is the case, for example, with bones and with some mussel shells. Bone mass is a powerful mix of minerals – primarily calcium carbonate – and proteins that provide the skeleton’s necessary flexibility. Thanks to this mixture, bones can be stretched or crushed to an extent that would not be possible if they were made of only one of the two materials.

But biomineralization has its limitations, as evidenced, for example, by how easily mussel shells shatter. "Just imagine how hard it would be to make a knife out of a brick – it’s the same if you want to make something sharp out of a biomineral," explains Robert Schofield.

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