Spider Webs Contain Ant Poison

Shichang Zhang, Teck Hui Koh, Wee Khee Seah, Yee Hing Lai, Mark A. Elgar, and Daiqin Li (2011), "A Novel Property of Spider Silk: Chemical Defence Against Ants," Proceedings of the Royal Society B: Biological Sciences (full text is behind a paywall).

Abstract: Spider webs are made of silk, the properties of which ensure remarkable efficiency at capturing prey. However, remaining on, or near, the web exposes the resident spiders to many potential predators, such as ants. Surprisingly, ants are rarely reported foraging on the webs of orb-weaving spiders, despite the formidable capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider. We explain this paradox by reporting a novel property of the silk produced by the orb-web spider Nephila antipodiana (Walckenaer). These spiders deposit on the silk a pyrrolidine alkaloid (2-pyrrolidinone) that provides protection from ant invasion. Furthermore, 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: while 2-pyrrolidinone occurs on the silk threads produced by adult and large juvenile spiders, it is absent on threads produced by small juvenile spiders, whose threads are sufficiently thin to be inaccessible to ants.

Posted on November 28, 2011 at 12:55 PM • 11 Comments

Comments

BlueRajaNovember 28, 2011 5:59 PM

"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"

Well, simple experiment to test that - Do spiders raised in environments with no ants still produce the chemical?

Bruce ClementNovember 28, 2011 7:29 PM

@BlueRaja

"while 2-pyrrolidinone occurs on the silk threads produced by adult and large juvenile spiders, it is absent on threads produced by small juvenile spiders, whose threads are sufficiently thin to be inaccessible to ants. " Abstract of the paper at The Royal Society website

BTW: Can you suggest an environment that has web spinning spiders and not ants?

MWNovember 28, 2011 8:31 PM

@BlueRaja:
That is not a valid test*. It supposes they've also evolved the ability to turn off the chemical in response to an ant free environment. (Such an ability is of course possible, but whether it makes evolutionary sense would be a function of cost of the chemical, the reliability of the spider's detecting an ant free environment, the expected cost of incorrectly ceasing chemical production, and the chance of the spider being in an ant free environment.)

* unless you're proposing to raise spiders in captivity for long enough for them to evolve a lack of the chemical, which would not be a 'simple experiment'.

NobodyspecialNovember 28, 2011 11:27 PM

It would be even more amazing if spiders hadn't developed a clever ant defence.
They have been successful land predators for 400myr, dinosaurs coming and going didn't even register.
They are so successful hunters they didn't even need to bother evolving the ability to fly - even though most of their prey does.
There are many 1cm long animals that can people single (well 8) handed.

NobodySpecialNovember 29, 2011 12:56 AM

Should have been:
There aren't many 1cm long animals that can kill people single (well 8) handed.

antNovember 29, 2011 4:18 AM

The experimenters could have verified that pyrrolidine alkaloid is an ant deterrent without having ants walk across silk thread bridges by spraying some pyrrolidine alkaloid at ants.

If the scientists are really interested to know whether ants don't walk on golden orb spider webs because of pyrrolidine alkaloid, they could set up another two thread bridges. One with the chemical the other without and for both bridges fasten a live golden orb spider at the end of the bridges instead of a dead fly.

Clive RobinsonNovember 29, 2011 6:09 AM

Hmm what other "wee beasties" don't like pyrrolidiene?

That is lets say just for arguments sake it's actually an anti fungal agent as well...

What steps have the scientists taken to rule out that the ant's dislike is actually not just a lucky secondary effect of another untested primary effect that is of more benefit to the spider?

SimonNovember 30, 2011 2:46 AM

Maybe ants have evolved the behaviiur of avoiding spider webs due to rampant predation.

Jerry A.December 15, 2011 4:15 PM

Clive:
If the pyrrolidine alkaloid has an as-yet unidentified anti-fungal activity or other useful activity, then you would expect to see the compound on all silk spun by this species, and not differentiated by thickness of the threads and or size of the spiders. Note that the alkaloid is turned off for thinner threads, which would be vulnerable to your hypothetical fungus.

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