Spider silk may not be quite as magical a substance as we’ve been led to believe, new research suggests. Scientists looked closely at the silk of several different spiders but were unable to find any with antimicrobial properties. The researchers say their findings should throw into question past claims of finding bacteria-fighting spider silk and that antibiotic silk should be considered nothing more than a myth.
Spider silk has long fascinated scientists and the public alike. The sticky substance, a protein-based fibre, is made by all known spiders, though its uses vary widely from species to species. There’s of course the classic web, but some spiders also rely on silk as a net to catch their prey. Some species use it in their mating rituals, while smaller ones float through the air on their strands. Others will just eat the silk that goes unused, as a sort of recycling. Given its versatility, it’s no surprise that humans in the past and present have tried to replicate the advantages of spider silk for ourselves.
One supposed attribute of silk is its antimicrobial activity, which piqued the interest of researchers at Aarhus University in Denmark. Social spiders live in close-knit communities with little genetic diversity — conditions that make them ripe for fast-spreading outbreaks of infectious disease. But if silk acts as an antibiotic barrier of sorts, they theorised, that might help explain why these spiders survive as well as they do. More hopefully, it could mean there are unique compounds that scientists could someday adapt from silk into antibiotics for human use, something we’ve long done with other natural sources.
The researchers kept coming up short, though. No matter the species or the germ that they used it against, the silk just didn’t seem to be antibacterial in the slightest. And once it was clear where things were heading, they started digging deeper.
“We were unable to detect the antimicrobial activity of social spider silk, and this made us curious about why other studies were able to detect antimicrobial activity in spider silk. We then started scrutinizing the papers reporting antimicrobial activity in every detail, and became aware of methodological shortcomings,” senior study author Trine Bilde, an evolutionary biologist at Aarhus, told Gizmodo in an email.
For one, there just hasn’t been much research on the subject in the first place, with many claims amounting to little more than anecdotal evidence. And among the few papers that have found some effect, the team spotted some possible fatal flaws. Some studies, for instance, seemingly didn’t try to account for the bacterial contamination of samples, which could have affected the growth of the other bacteria scientists were actually studying. Many also didn’t appear to try controlling for the effects of the solvents used to extract the spider silk, some of which are known to have their own antibacterial properties, like ethyl acetate.
A crucial part of scientific research is replication. And when Bilde and her team ran experiments with seven different types of spider silk found to have antimicrobial activity in the past, they found no activity at all this time. The results of their paper — titled “The Myth of Antibiotic Spider Silk” — were published Tuesday in iScience.
Despite that title, Bilde doesn’t close the door entirely on this area of research. It’s possible that someday other scientists really will come across antimicrobial silk from a specific spider or debunk this debunking. But for now, she said, scepticism should be the default, and future studies should be designed to avoid the mistakes documented by her team. “We can still test the idea in new species and with new test microbes, but with a more cautious starting point,” she said.
It’s also possible that silk isn’t completely useless against microbes. Because silk is commonly used to protect spider eggs, an easy prey for some bacteria and fungi, Bilde noted, it may have yet properties that act as a physical barrier against worrying germs. Some research has suggested that this could explain why silk stays rot-free for so long. Other scientists have created synthetic silk that can be infused with existing antibiotics, in hopes of one day developing improved wound dressings.
As for any Tobey Maguire as Spider-Man fans out there, don’t worry: The list of things spider silk can do is still very lengthy.
“Spider silk has extraordinary properties,” Bilde said. “There are lots of other functions that are still unknown and worth studying, such as the strength and elasticity of silk, properties that would be useful for developing more applied applications.”