Chemical Deterrent to Ant Attack Discovered in Spider Silk
29 November 2011
"We found that large Golden orb web spiders add a defensive alkaloid chemical onto the silk, which stops the ants from walking onto the web when they come into contact with it."
Assoc Prof Daiqin Li, NUS Department of Biological Sciences.
The Golden orb spider is typically found in the forests of Australia, Asia, Africa and America
(Photo credit: Assoc Prof Daiqin Li)
Researchers from NUS and the University of Melbourne found a chemical deterrent, pyrrolidine alkaloid, in spider silk which may offer new prospects for pesticide design. Their study was published in the journal Proceedings of the Royal Society B in November 2011.
"We found that large Golden orb web spiders add a defensive alkaloid chemical onto the silk, which stops the ants from walking onto the web when they come into contact with it," said Assoc Prof Daiqin Li of the NUS Department of Biological Sciences (DBS).
The NUS team consisted of Mr Zhang Shichang, Dr Koh Teck Hui, Dr Seah Wee Khee from NUS DBS and Assoc Prof Lai Yee Hing from the Department of Chemistry.
Prof Mark Elgar from the Department of Zoology at the University of Melbourne said that pyrrolidine alkaloid acts as a predator deterrent in many species of ants, moths and caterpillars.
"The orb spider is potentially vulnerable to attack from groups of ants while sitting in its web waiting for prey, so the chemical defense in web silk may have evolved to not only protect the spider, but to reduce the time and energy that would otherwise be required to chase away invading ants," said Prof Elgar.
The team's research was prompted by their curiosity over why ants rarely occur on the web of orb web spiders, despite their abundance.
Having the Golden orb web spiders spin webs in the lab, the research team devised three experimental settings – first with the pyrrolidine alkaloid removed from the silk, then with the chemical added to it and finally leaving the webs as they are. The ants were able to cross the cleaned silk but were unable to cross in the two cases where pyrrolidine alkaloid was present.
The team also found that only large Golden orb web spiders produce the defensive compound, suggesting that the younger, smaller spiders could rely on their thinner web silk to physically prevent ants being able to climb into their webs. The Golden orb web spider (Nephila antipodiana) is commonly found in the forests of Australia, Asia, Africa and America.