Spider webs catch more than prey. They’re also jam-packed with animal DNA

Josh Newton probably isn’t very popular with spiders. After all, the Australian scientist has a tendency to go around undoing their hard work. 

“I liken it to when Princess Fiona in Shrek makes some cotton candy for Shrek from spider webs, where she collects a stick and just wraps around the spider web for him. But I do it with a clean, sterile stick,” Newton, a PhD candidate in life sciences at Curtin University, told As It Happens host Nil Köksal. 

“And then I just wrap the spider web up and put it in a little tube and bring it back to the lab.”

But he has a good reason. Spider webs, it turns out, trap more than unwitting bugs. The sticky surfaces also contain a bounty of genetic materials from dozens of animal species who live nearby — making them a powerful tool for measuring biodiversity. 

In a new study, Newtown and his colleagues identified DNA from 93 different invertebrates on spider webs in Perth, Australia. The findings were published last week the journal iScience.

You’re breathing DNA right now

The study is just the latest innovation in the emerging scientific field of studying environmental DNA (eDNA) — genetic material that all living creatures shed as they move around the world, often in the form of dead skin cells.

In recent years, scientists have collected DNA from soil, water, plants and more. It can even be pulled from the air. 

Earlier this year, conservationists used environmental DNA to track down an elusive species of golden mole in South Africa that had been feared extinct.

“Every single thing seems to be covered in environmental DNA,” said Elizabeth Clare, a molecular ecologist at Toronto’s York University who was not involved in the study. “Every breath of air you breathe in has DNA in it.”

Newton says the idea to check spider webs for animal DNA came from his PhD supervisor, Morten Allentoft.

“He was walking in a wetland near where we live and saw a giant web, and it kind of just kind of clicked. And he thought, ‘Oh, surely this is going to work.'”

Scientists have used webs to collect the DNA before, but only of spiders that built them, and the insects they prey upon. This is the first time researchers have extracted invertebrate DNA from webs.

They first collected webs from an animal sanctuary in Perth, and identified DNA from 32 different species, including native mammals and birds. 

But scientists don’t know how far eDNA travels, or how long it lasts, so the researchers couldn’t be certain the DNA they found was from animals currently living nearby.

So they repeated the experiment at the Perth Zoo. Sure enough, they found DNA from 61 different invertebrate species that, by and large, matched the composition of the zoo.

“So elephants and rhinos and kangaroos in the spider webs,” Newton said.

Clare says says that by conducting their research at a zoo — where they knew exactly where the animals were located in relation to the webs — the study’s authors have helped unravel some of the mysteries of eDNA. 

“We’re really lacking in information about how far the [genetic] material can move, and its persistence,” she said. “So scientifically, the most interesting thing is that it’s helping us narrow down the idea of where it may travel to and how far it can go.”

Quick, cheap and easy

Mark Louie Lopez, a University of Victoria researcher who works with first nations to monitor eDNA in Alberta lakes, says using webs to collect DNA is a clever innovation.

Often, he says collecting genetic material on land means  swabbing trees and leaves, taking soil samples, or studying blood-sucking creatures like leeches and mosquitoes.

“Collecting spider webs is a considerably quicker method … and it also avoids issues caused by the presence of organic inhibitors (for example, tannins found in soil) that make DNA detection more difficult,” Lopez, an  iTrackDNA and Liber Ero postdoctoral fellow, told CBC in an email. 

“It’s astonishing how creative researchers have been in using eDNA for biodiversity monitoring.”

Both Clare and Lopez caution that eDNA alone is limited in scope. For example, you can tell what animals are around, but not how many. So when it comes to measuring biodiversity, it’s just one tool in the scientific toolbox.

Currently, one of the most powerful methods of collecting airborne DNA is to extract it from air filters — a technique pioneered by Clare and her colleagues.

WATCH | York University scientists collect eDNA from air filters: 

But filters require electricity. And scientists have to either install them, or collaborate with the countries and governments already operating them.

“This is quite a bit simpler,” Newton said. “We just walk out into the environment and the spider webs are just there and they’re very easy to collect. And they’re everywhere, pretty much, spider webs.”

Everyone wins, he says — except, perhaps, the hardworking spiders. 

“It would be nice to find something that work just as well that that didn’t impact the spider,” Newton said. “We’re working on that.”