Meet Peckhamia, a charmingly ant-like jumping spider:
Peckhamia is a common ant-mimicking jumping spider in North America (photographed in Urbana, Illinois).
Peckhamia avoids being eaten by predators by appearing like an ant rather than a spider. This defense is two-fold. Ants aren’t as palatable as spiders to most general predators, and spider-specialized predators might not recognize Peckhamia as food.
For mimicry to work optimally, though, spiders must inhabit places with plenty of ants. Not the easiest task, since ants eat spiders. And because most ants have poor vision, the spider’s physical resemblance to ants isn’t much help.
So how does this ant mimic spider escape being attacking by ants?
A new paper by Divya Uma et al in PLoS One provides a partial answer: Peckhamia doesn’t smell like a jumping spider. It doesn’t smell like an ant, either, so it’s not a chemical ant mimic. In fact, Peckhamia doesn’t smell like much at all. Look at the results of Uma et al’s cuticular hydrocarbon assay:
Figure 5 from Uma et al 2013, showing that Peckhamia have lower amounts of cuticular hydrocarbons than both the ants they mimic, and non-mimic species of jumping spiders.
Cuticular hydrocarbons are chemicals that impart odor, and Peckhamia has rather low amounts of these. It’s a stealth spider!
The researchers also measured predation rates by spider-eating wasps on Peckhamia (lower than on related species), and rates of attack by ants (lower against mimic spiders than against non-nestmate ants). I’d have liked to see the next step of actually painting hydrocarbons on the mimics to gauge the ants’ reaction, but even without that experiment the odorlessness of Peckhamia is an intriguing observation.
[for more ant mimics, see my ant mimic photo gallery]
source: Uma D, Durkee C, Herzner G, Weiss M (2013) Double Deception: Ant-Mimicking Spiders Elude Both Visually- and Chemically-Oriented Predators. PLoS ONE 8(11): e79660. doi:10.1371/journal.pone.0079660
Over at Compound Eye I’ve posted photos of a remarkable Australian ant-mimic spider:
An Enemy in the Ranks
Ants cross a strand of spider silk without 2-pyrrolidinone (top), but avoid the strand with the repellent (bottom). Adapted from Figure 1 of Zhang et al 2011.
One measure of a predator’s ecological significance is the abundance of strategies prey adopt to avoid being eaten. And how ecologically significant are ants?
They are enough of a problem to web-building spiders that the arachnids impregnate their webs with ant-deterring 2-pyrrolidinone:
…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.
These results were reported today in a paper by Shichang Zhang in Proceedings of the Royal Society B. Zhang et al assayed three species of ants against an array of silk strands with and without the alkaloid, finding they would more frequently traverse the 2-pyrrolidinone-free strand to reach a food source. It’s good, basic experimental chemical ecology.
I do have one quibble with the study, though. The authors wanted to test the efficiency of 2-pyrrolidinone against ants generally, so they employed several ant species. But their subjects (Pheidole angulicollis, Monomorium pharaonis, and Monomorium indet. sp.) are all relatively similar ants in the subfamily Myrmicinae, and ones I’m not sure represent much of a predation risk for Nephila spiders in nature. Singapore has large, dominant tree-dwelling ants- including the formidable Oecophylla weaver ants- that likely are more dangerous to spiders and would have presented a more realistic test of the spider’s chemical defenses.
source: Zhang, Koh, Seah, Lai, Elgar & Li. 2011. A novel property of spider silk: chemical defence against ants. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2011.2193
Loxosceles reclusa, the brown recluse
Among the more interesting animals to appear at the BugShot photography workshop was a Loxosceles reclusa caught wandering about the basement of the assembly building. I had never seen one before.
Most of us are taught to recognize the famously venomous recluse by a violin-shaped pattern on the spider’s back. But other species, including some common wolf spiders, sport similar markings, so it is better to make use of eye arrangement to confirm the identification. The recluse’s eyes are grouped, unusually, into three clusters: a central pair and two lateral pairs, clearly visible in the photograph above. Continue reading →
Sometimes I’m glad not to be a grasshopper:
Anelosimus sp. social spiders (Ecuador)
Nothing freaks out the arachnophobe in me more than social spiders. One of the more common arachnids in tropical forests, these spiders spin communal webs with hundreds or thousands of individuals.
Anelosimus, up close
Canon EF 100mm f/2.8 macro lens
Canon EOS 7D
(top) ISO 400 f/11 1/250 sec
(bottom) ISO 200 f/14 1/250 sec
(middle)Tamron 11-18mm wide angle zoom
ISO 800 f/7 1/25 sec
Arachnids (you know, spiders and mites and things) never had much of a presence in my photo galleries. While I could chalk their absence up to an obsessive focus on formicids, the reality is that I’m mildly arachnophobic. Photographing spiders makes me squirm, so I don’t do it very often.
Oddly, it really is just spiders. I don’t have any trouble with opilionids, mites, or even scorpions. And it isn’t all spiders, either. I’m rather fond of salticids. But there’s something about the form of some spiders that touches off a deeply instinctual revulsion. Embarrassing for an entomologist, but there it is.
Anyway. The last seven years of photographing nature has brought a reluctant accumulation of arachnid photos, and I’ve finally collected enough to put them in their own gallery:
Arachnid photos at alexanderwild.com
Widow spider and harvester ants. Hallelujah Junction, California
This young black widow (Latrodectus hesperus) set up shop above the nest entrance of a colony of Pogonomyrmex harvester ants. It’s an all-you-can-eat buffet, allowing the spider nearly unlimited pickings as the ants come and go.
The spider’s mottled coloration is typical of young widows; they don’t acquire the striking black and red warning garb until maturity.
photo details: Canon 100mm f2.8 macro lens on a Canon EOS D60
ISO 100, 1/200 sec, f/11, MT-24EX twin flash
Take that, vertebrate scum!
Incidentally, my wife used to have one of these Nephila spiders nesting in the high ceiling of her living room when she was living in Queensland. I guess she used it to dissuade potential suitors, but somehow I made it through.
My lovely wife Jo-anne has been in South America the last couple weeks doing field research on Argentine ants while I tend the home fires here in Tucson. I hope she finds it in her to forgive me for the post I am about to write.
Earlier today I got an email explaining why I’m not getting my much-awaited phone call:
I’d call but there aren’t any phones at this locutorio and we’re on our way out to look for social spiders.”
Excuse me? Social spiders? More important than me, your needy hubby?
Ok, I grant that social spiders are pretty cool, if a bit creepy. I remember those things from when I lived in South America. They spun massive webs that spanned tree-tops, anchored to the ground with tow lines as strong as steel cables. I nearly died from shock the first time I saw them. I had accidently walked under their tree, a large Enterolobium, and looked up to find the sky speckled with thousands of grape-sized spiders, all sharing a web tens of meters across. It still gives me the willies to think about.
A few years later I had a camera handy when a Paraguayan friend and I drove past what looked like a small body caught up in Shelob’s web. We stopped.
Turned out not to be a single body, but hundreds of little hairy bodies that had fastened several branches into a little cradle. Social spiders!
From close in:
Social spiders are something of a mystery. They don’t share all the traits that have tipped the more famously social ants, bees, wasps, and termites into cooperative living. Yet it appears that nearly a dozen independent lineages of spiders have converged on a cooperative lifestyle. There must be something advantageous in it for the spiders, and that question continues to attract inquisitive scientists like Jo-anne.
Still, which do you think is better? Me? Or that twitching arachnoid mass of legs? And anyway, wouldn’t calling me be *safer* than going out looking for those things?