Australasian Science: Australia's authority on science since 1938

RepellAnt in Silk

By Stephen Luntz

Silk produced by golden orb-weaving spiders contains ant repellent.

The silk produced by golden orb-weaving spiders is not merely strong, elastic and colour-coded to match locations, but it also contains ant repellent.

Ants represent more of a threat to spiders than potential prey, so it makes sense for spiders to keep them off their webs. Prof Mark Elgar of The University of Melbourne and a team from the National University of Singapore wondered why ants were so rarely observed on orb-weaver webs, despite their often-close proximity.

After washing silk from golden orb-weaving spider webs, Singapore’s Daiqin Li detected the presence of 2-pyrrolidinone, an alkaloid known to repel ants and moths.

“We encouraged ants to forage on a bait and took advantage of the fact they go straight back to their nests afterwards,” Elgar says. “We offered them three bridges to cross, one made of natural orb-weaver silk, and two with the chemicals washed off. They avoided the natural bridge and used the other two.”

The researchers added a drop of distilled water to one bridge and 2-pyrrolidinone to the other. The ants continued to use the watered bridge, but abandoned the one treated with the alkaloid.

Li says 2-pyrrolidinone is not a candidate for new insect repellents as it is believed to have carcinogenic properties. However, it is possible it may serve as a lead molecule towards more useful alternatives.

The coating of the silk clearly does not deter flying insects from blundering into the web, and Elgar says it may even be useful. “It may cause an insect to struggle more, and the more it struggles the more tightly it becomes entrapped.”

Smaller spiders do not produce the 2-pyrrolidinone, which the researchers attribute to their strands being too thin for ants to traverse.

The research was published in Proceedings of the Royal Society B.