A team around Mark Elgar, University of Melbourne, Australia, discovered that 2-pyrrolidinone is present on the silk of the orb web spider Nephila antipodiana and demonstrated that it deters workers of three species of ant. Such compounds are commonly employed as chemical defence mechanisms in many species of ant, moth and caterpillar, but this is the first time spiders have been found to be using it.

Using gas chromatography-mass spectrometry, they found that the chemical is only present on silk threads produced by adult and large juveniles, and absent on threads produced by small juveniles. The thinner silk of juveniles is insufficient to allow ants to traverse. The ontogenetic change in the production of 2-pyrrolidinone suggests that this compound represents an adaptive response to the threat of natural enemies, rather than a simple by-product of silk synthesis.

The use of a fairly simple chemical as an ant repellent is the most interesting aspect of this finding.

• A novel property of spider silk: chemical defence against ants,
  Shichang Zhang, Teck Hui Koh, Wee Khee Seah, Yee Hing Lai, Mark A. Elgar, Daiqin Li,
  Proc. R. Soc. B 2011.
  DOI: 10.1098/rspb.2011.2193