If Spider-Man really could do “whatever a spider can”, he ought to shoot webs from somewhere less salubrious than his hands. All spiders spin silk from their rear ends, using special organs called spinnerets. But one group – the tarantulas – can also shoot silk from their feet, and they use this ability to climb up sheer vertical surfaces.
Tarantulas have been kept as pets for decades, but their silk-spinning feet were only discovered in 2006 by Stanislav Gorb from the Max Planck Institute. Gorb watched Costa Rican zebra tarantulas climbing up glass plates, and saw that they left behind silken footprints – dozens of fibres, just a thousandth of a millimetre wide.
As the spider climbs, four of its legs leave the glass plate at any one time. As the legs land, they begin to slip but small nozzles secrete a viscous silken fluid that rapidly hardens and adheres to the surface. The silk acts as a tether, firmly holding the spider to the pane.
It was a fascinating story, but three years later, Fernando Pérez-Miles claimed that Gorb had got it wrong. He found that zebra tarantulas could no longer secrete silk if their spinnerets (the ones on their backsides) were sealed. He argued that the spiders brush the spinnerets with their hind legs when they walk; it’s this motion that releases silk threads.
Now, Claire Rind from Newcastle University has weighed in on the matter, and she sides with Gorb. Rind bought three Chilean rose tarantulas from local pet stores, placed them on glass slides, and filmed them as she gently raised the glass to a vertical position. The spiders didn’t fall, even when Rind gently shook the glass. Their legs slipped slightly, but they soon regained their footing, and every time, they left tiny silken threads behind. That’s essentially what Gorb found; to seal the case, Rind had to find the structures that secrete the silk.
She gathered moulted skins from three species of tarantula, including her own recently deceased pet – a Mexican flame-knee tarantula called Fluffy. Under an electron microscope, Rind saw strands of silk emerging from the tips of several hairs (‘setae’) on the feet.
Setae usually end in brush-like tips, and they’re part of a spider’s climbing equipment. The tips make close contact with the microscopic bumps that cover every surface (even smooth ones), and they stick using the same forces that hold molecules together. But among the brush-like setae, Rind found others that were tall, ribbed and tapered. Each had a small hole at its tip, and one of them even had a droplet of silk coming out of it. Tarantulas can spin silk from their feet, and here was the evidence.
The silk-spinning hairs (Rind calls them ‘spigots’) are much taller than the surrounding setae, like skyscrapers in a low-rise suburb. This allows them to produce silk without gumming up the spiders’ feet. They’re spaced out so they don’t stop the other setae from touching the surface, and they’re ribbed so that they don’t get crushed when the spider walks.
Gorb suggested that tarantulas evolved silk-spinning feet because they need a third method of sticking to surfaces, beyond their claws and their setae. They are among the largest of all spiders, and they would be killed by falls that smaller species would shrug off. The spigots on their feet give them an extra lifeline – a way of avoiding a fatal fall when all other ways fail.
Rind agrees, and she thinks this could explain why Pérez-Miles didn’t find any silken threads in his experiments. He placed his spiders in a shallow tank and never tired to shake them off. They didn’t need their silken lifelines – their setae and claws were good enough.
The ability to spin silk from their feet could have evolved several times among the larger tarantulas, to help them support their large bulk. If that’s the case, the smallest tarantulas (some are less than a millimetre long) shouldn’t have any spigots, and that’s something for other scientists to check. But Rind thinks that this story is an unlikely one.
She worked with three tarantula species– the Chilean rose, the Mexican flame-knee, and the Indian ornamental – that are all distant relatives. It’s more likely that the ancestor of all tarantulas could spin silk from its feet. In fact, it’s even possible that tarantula foot spigots might represent the silk-spinning organs of the earliest spiders. Perhaps they were precursors to the more sophisticated spinnerets, which could have evolved from modified legs.
Reference: Rind, Birkett, Duncan & Ranken. 2011. Tarantulas cling to smooth vertical surfaces by secreting silk from their feet. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.055657
Gorb, Niederegger, Hayashi, Summers, Vatsch & Walther. 2006. Biomaterials: Silk-like secretion from tarantula feet. Nature http://dx.doi.org/10.1038/443407a
Pérez-Miles, Panzera, Ortiz-Villatoro & Perdomo. 2009. Silk production from tarantula feet questioned. http://dx.doi.org/10.1038/nature08404
A gallery of incredible spiders
May 16th, 2011 at 7:59 am
I’ve just nearly fallen off my chair when the front page loaded.
I swear these creatures are the embodiment of pure evil
May 16th, 2011 at 9:02 am
Nah, spiders are cool. Great article!
May 16th, 2011 at 10:00 am
But I guess Pérez Miles results hold, since he published on the zebra tarantula, a different species from the three that Rind used for her research. It seems likely that some tarantulas can secrete silk from their feet but others cannot.
May 16th, 2011 at 10:26 am
Great article. One of the best I have read at showing how science works. By the way, the photo-micrographic proof set is superb.
May 16th, 2011 at 10:39 am
Interesting article, I’ve been keeping tarantulas for a long time and been following this ‘controversy’. Good follow up. Would be interested in seeing the same experiment done with the ‘zebra’ spider.
It’s always incredible watching my rosie scram up a sheer glass surface. She’s got a lot of bulk to carry, freaks newbies out.
Also, curious why you didn’t include the scientific names? Common names in the tarantula world are pretty messy.
May 16th, 2011 at 12:12 pm
wut
May 16th, 2011 at 12:18 pm
I wouldn’t be surprised if some spiders grabbed silk from their spinnerets to do the same thing, but I’d think someone could film that happening.
Nice work, Ed. Always intriguing when a whole new structure is discovered on a well-known species.
May 16th, 2011 at 12:33 pm
Jeez, I gotta second I’m Oscar @#1. I try to fight my mild phobia by learning interesting stuff about arachnids, but it is completely unhelpful to get zotzed with a giant color photo at the top of the story. I was expecting it, but even so–a smaller image one could click to enlarge, especially if it loaded a little further down the page, would be a lot easier to handle.
Spiders are cool, but if there *were* an embodiment of pure evil, that one up there would be in the running.
May 16th, 2011 at 1:33 pm
I’m with “I’m Oscar” on this one, lol.
May 16th, 2011 at 2:20 pm
Jeez, you massive bunch of babies. Just for you lots, I am now trying to locate a picture of two kittens taped together (eight legs, you see?) to replace the one of Fluffy.
Poor rejected Fluffy.
May 16th, 2011 at 3:05 pm
Aww, nooo! I love Fluffy.
May 16th, 2011 at 8:26 pm
Actually, that’s quite a beautiful animal. Yellow jackets are the true embodiment of pure evil. Nasty little buggers. I suppose if I were studying them I might find a redeeming quality or two. Nah, I prefer to believe they have no redeeming qualities. We all have our prejudices and mine involve things that sting me for no apparent reason.
May 17th, 2011 at 3:49 am
I just love a B. auratum
very educating article.
May 17th, 2011 at 4:10 am
Excellent work again, Ed.
I have a couple of (genuine, rather than truculent) questions about this paragraph:
“The ability to spin silk from their feet could have evolved several times among the larger tarantulas, to help them support their large bulk…
1. Could it not equally be that the ability to spin from their feet allowed them to evolve into bigger spiders?
2. The ability to cling is certainly helpful, but is a spider likely to encounter much as smooth and vertical as glass in the wild?
All of the above could be true, or maybe Rind’s tarantula was bitten by a radioactive spider – does it have a little red mask? Spiderspider.
May 17th, 2011 at 5:35 am
Wasps are pure evil, specifically those that prey upon tarantulas. This is a fine article, one that is well written, well researched, and just utterly what is needed to dispel misinformation. I just read a story about 20 minutes ago about the german tarantula peddler that was arrested – they called tarantulas 1) poisonous and 2) deadly.
I ended up rage-replying >_>
Tarantulas are not the embodiment of evil. In fact, I’d look a little closer to home at our own species before I really put the blame on wasps :p
Anyways, I love the pictures, and the detail, it is stunning.
@Steve, sizes have always been larger in the past than now in terms of arthropods, I believe it had more to do with available oxygen in the atmosphere to metabolize quickly rather than structural integrity – although even with optimal oxygen there would be of course some size restrictions from gravity itself. This is likely an ancient evolutionary trait (in my opinion anyways) that appeared with the first Mygalomorphs (probably misspelled that). A real test would be to see if it was in Mesothelae (The oldest of the spiders currently alive). As was also hinted at, this could be where silk laying started – with the feet instead of the abdomen.
As for 2: They have adapted to all kinds of surfaces for maximum survivability. They have a hard time with glass as it is (I have watched mine) in terms of the terrestrial tarantulas, however with arboreal I am sure they are more finely tuned and better adapted, since they have to deal with slick and/or wet leaves, mossy surfaces, and smooth limbs of tree branches. There’s a lot of smooth surfaces in nature, and while glass may be a bit smoother than a leave with drizzle, nature seems to have a tendency to overcompensate when there is no pressure not to do so.
May 17th, 2011 at 5:43 am
Wasps *are* evil. The entire fourth episode of Life in the Undergrowth could basically have been titled “Wasps are bastards”. Also, I find Fluffy really quite beautiful. Now the chihuahua – there’s a monstrous disturbing animal if ever I saw one.
I digress.
@Sleve – “Could it not equally be that the ability to spin from their feet allowed them to evolve into bigger spiders?” Well sure, but then you’re back to the question of why they evolved the ability to spin from their feet? That explanation was an attempt to reconcile the fact that silk-spinning feet only seem to have evolved in large spiders. Also, I *love* spiderspider. See also: Manman.
May 17th, 2011 at 7:09 am
Excellent piece.
The evolutionary implications of these ‘primitive’-seeming silk spigots on the feet are fascinating. I am really curious to know where this foot-silk shows up the larger evolutionary framework of spiders. My colleague Gillian’s thesis gets into the fact that spider silk, in general, seems to be a particularly useful trait to taxonomists trying to trace the evolutionary history of spiders. It the genes associated with silk production are apparently quite prone to mutation and therefore rife with novel features that are easy to track.
Also, something mentioned here that is always startling for me to realise: tarantulas will go splat if they take a high fall. I’m so used to thinking of arthropods as safe from gravity due to small size, tough exoskeletons, and low terminal velocities. It’s just interesting to appreciate how much selective pressure tarantulas must be under as a product of their size; they have to be more circumspect than other spiders.
Lastly, I’ll second the love for spider-spider. (And, to be fair, in classic Spider-Man canon he devised artificial webshooters, thereby neatly bypassing the awkward need for any insalubrious glands.)
May 17th, 2011 at 7:37 am
My initial comment was more light-hearted than it might have come across.
As always, superb writing Ed.
But they are still the embodiment of pure evil
May 17th, 2011 at 11:26 am
Interesting article. My first reactionwas skepticism (it is always my first reaction), but the SEMs make a convincing case. Also, spider mites spin silk from a seta on their palps – just another serial homologue of a leg as are the chelicerae. Snout mites like Spinibdella species seem to shoot the silk they entrap their prey with from their chelicerae (or at least their mouth openings) and, of course, Scytodes spiders do the same. I’ve always suspected that arachnid silk would be derived from modified nephridia associated with limbs (feel free to feel skeptical).
May 17th, 2011 at 2:28 pm
Hmm… The book “Life in the Undergrowth” didn’t seem too harsh toward wasps… except, perhaps, the parasitic ones that inject their eggs into live, paralyzed creatures to be devoured from the inside out. That, I suppose, is a little bastardly.
The spider Fluffy, however, is quite beautiful. I’m considering what kinds of insects/arthropods/invertebrates I’d like to keep (wife willing), and while I’m not sure about tarantulas, I could keep them in mind.
May 17th, 2011 at 7:45 pm
While I usually decline to assign loaded words to species, there might be an exception or two. I was quite blown away by the Japanese Giant Hornet.
http://en.wikipedia.org/wiki/Asian_giant_hornet
These creatures actually prey upon other bees, and their attack methods are gruesome. They wipe out entire hives!
In a neat twist however, indigenous Japanese honeybees have developed a defense. They mob the attacking hornet and use a remarkable strategy to fight back! I won’t say more; click on the link if you’re curious.
May 17th, 2011 at 7:57 pm
They bake the hornets to death.
Yes, but did you know that Cyprian honeybess also defend themselves against hornets by piling on top of them? And they use an entirely different strategy to kill.
May 17th, 2011 at 11:55 pm
I have more than a few things to say about this article so I posted them to my blog, here: http://annepeattie.com/2011/05/17/can-silk-help-tarantulas-climb/
To summarize: silk may help tarantulas climb, but it’s likely a small effect, and anyway that’s not what the paper was about, their title notwithstanding.
May 18th, 2011 at 2:50 am
So spiderman must have caught tarantula genes
I love the mix of complexity between simply tipping a spider around on a watchglass and using super-duper microscopes to find the apparatus behind their sticking power.