This golden orb spider (Nephila antipodiana knows how to keep ants off its web.
Credit: Daiqin Li
SYDNEY: The web silk of a golden orb spider contains a repellent to ward off ants, which researchers have likened to chemical weapons.
Researchers have discovered that the golden orb spider (Nephila antipodiana) uses chemical compounds called pyrrolidine alkaloids, which are commonly used as a defence mechanism by many arthropods (a group containing spiders, insects and crustaceans), to repel invading ants from storming their webs.
The discovery resolves an intriguing paradox surrounding the relationship of ants and spiders that scientists have struggled with for years.
"Ants and spiders are found in the same habitat, but ants rarely venture onto the webs of spiders - despite the resources available on the web and the ability of ants to overcome potential prey," said Mark Elgar, evolutionary biologist from the University of Melbourne and co-author of the study published in the current issue of Proceedings of the Royal Society B.
Nature's chemical weapons
The golden orb spider is found mostly South East Asia, as well as in the Solomon Islands and North Queensland. Named after the unique golden colour of their web, the species consumes and rebuilds their web every few days. The female of the species is considerably larger than the male.
The web, along with the remains of any insect carcases and the spider itself, are considered by scavenger animals to be easily accessible and nutritional food, so it was a mystery why ants stayed away.
The team realised that the chemical compound acted as a deterrent when they extracted the compound from the silk and tested it on the ants. "[We] found that the ants would frequently cross the bridges comprising silk threads without [the] compound, but they rarely [crossed] the bridges with [it]," said Daiqin Li, a biologist from the National University of Singapore and co-author of the study.
Spiders build webs that are strong, elastic and adhesive to catch smaller insects. Most of their day is spent sitting and waiting for this to occur. If they didn't have the chemical compound in their webs, they would have to expend large amounts of energy on chasing away predators, like ants, leaving little time to feed or build new webs. "It highlights a novel form of chemical defence that is in direct response to the threat of enemies," said Elgar.
Mariella Herberstein from Macquarie University in Sydney, a biologist who was not involved in this study, said the research showed a novel way of explaining the lack of ant invasions in the web, considering that web silk is pure protein. "[The next step is] to look at web silks from a more holistic perspective to understand the multitude of functions that silk needs to provide," she said.
More effective ant repellent
Aside from the new knowledge of spiders, Elgar said there are possibilities to apply the chemical to the controlling of ant colonies in the home. "It would be interesting to explore the bio-control potential of the ant repellent," he said.
Li said the next step was identifying where in the spider the chemical was produced, as well as testing other spiders webs for similar repellents.
