"Tarantulas eject silk from feet"

[esotericman]

Well, finally something I can easily do within my own collection. Thanks for the pointers, I had not thought of keeping things closer to the stub. I swear, I forget my brain at home some days.

 

[JDeRosa]

T's can shoot silk from their feet???

http://www.foxnews.com/scitech/2011/05/18/tarantulas-shoot-silk-feet-researchers/?test=faces

 

[KoriTamashii]

Ha. Neat articles.

 

[Bigboy]

Silk secretion from tarsi! Newest publication shows silk secreted in feet!

New publication from the journal of experimental biology. I was quite surprised.

Title:
Tarantulas cling to smooth vertical surfaces by secreting silk from their feet

Authors:
Rind, FC; Birkett, CL; Duncan, BJA; Ranken, AJ

Source:
JOURNAL OF EXPERIMENTAL BIOLOGY, 214 (11): 1874-1879; JUN 2011

Abstract:
Like all spiders, tarantulas (family Theraphosidae) synthesize silk in specialized glands and extrude it from spinnerets on their abdomen. In one species of large tarantula, Aphonopelma seemanni, it has been suggested that silk can also be secreted from the tarsi but this claim was later refuted. We provide evidence of silk secretion directly from spigots (nozzles) on the tarsi of three distantly related tarantula species: the Chilean rose, Grammostola rosea; the Indian ornamental, Poecilotheria regalis; and the Mexican flame knee, Brachypelma auratum, suggesting tarsal silk secretion is widespread among tarantulas. We demonstrate that multiple strands of silk are produced as a footprint when the spider begins to slip down a smooth vertical surface. The nozzle-like setae on the tarsi responsible for silk deposition have shanks reinforced by cuticular thickenings, which serve to prevent the shanks' internal collapse while still maintaining their flexibility. This is important!
as the spigots occur on the ventral surface of the tarsus, projecting beyond the finely divided setae of the dry attachment pads. We also reveal the structure and disposition of the silk-secreting spigots on the abdominal spinnerets of the three tarantula species and find they are very similar to those from the earliest known proto-spider spinneret from the Devonian period, giving another indication that silk secretion in tarantulas is close to the ancestral condition.

 

[Lawnmower599]

i saw this on the news before school and i don't think they can make this decision just through the g.rosea as this is just one tarantula and i think most of you would agree that further result should be followed through to ultimately say that web is released through a tarantulas feet

but it still is impressive

 

[Kirk]

i saw this on the news before school and i don't think they can make this decision just through the g.rosea as this is just one tarantula and i think most of you would agree that further result should be followed through to ultimately say that web is released through a tarantulas feet

but it still is impressive

Read the above abstract.

 

[sjl197]

Can anyone explain to me the evolutionary selective pressure why terrestrial 'burrowing' species should have such elaborate 'non-slip' structures on the underside of their feet, as i'd be curious to know the answer.

Do tarantulas commonly encounter surfaces like glass in nature? I actually dont think so, sorry, i cant see the selective pressure. The only surface i can think of is waxy leaves, but how often do tarantulas really want or need to walk on such surfaces? Avicularia occasionally perhaps, juveniles of a few arborial species, but thats about it i would think. Few species, rarely. Especially the burrowing species, really, why have such a mechanism to allow them to walk on slippery surfaces when they never encounter such surfaces in nature ??! You generally find a tendency in nature that can be best described as 'use it or loose it'. If a structure or behavor is useless for survival or reproductive success, it generally disappears, which is why for example tarantulas living in dark caves seem to become eyeless. Especially if the structure/behaviour is metabolically costly, as silk production surely is. Even the arboreal species., isn't tree bark really rough enough for them to grip with claws and their more elaborate scopulae?.

Hairs on the tarsi with ducts, ok im convinced. But, what makes these structures silk producing? Why are these not thermosensory setae with open ducts, that exist to detect temperature differences?, i can see why many different tarantulas would benifit from those... silk producing tarsal structures...im not convinced, sorry.

 

[Kirk]

Can anyone explain to me the evolutionary selective pressure why terrestrial 'burrowing' species should have such elaborate 'non-slip' structures on the underside of their feet, as i'd be curious to know the answer.

Maybe the selective pressures, if any, were not among burrowers. What is observed today among burrowers is just a phylogenetic free ride.

Hairs on the tarsi with ducts, ok im convinced. But, what makes these structures silk producing? Why are these not thermosensory setae with open ducts, that exist to detect temperature differences?, i can see why many different tarantulas would benifit from those... silk producing tarsal structures...im not convinced, sorry.

Just a matter of doing some TEM.

 

[BrynWilliams]

having sticky feet is a massive advantage in 'escape and evade' that slings use all the time. additionally, the 'sticky' feet are very well designed for moving across the fibres of their webbing and nabbing prey.

I'd venture that the ability to walk on wet glass obviously isn't something that a T does in the wild at any stage, but perhaps is a consequence of selection pressures elsewhere in the lifecycle.

Can anyone explain to me the evolutionary selective pressure why terrestrial 'burrowing' species should have such elaborate 'non-slip' structures on the underside of their feet, as i'd be curious to know the answer.
.

 

[Zoltan]

Another recently published article is related to this:

Peattie, A. M., J.-H. Dirks, S. Henriques & W. Federle. 2011. Arachnids Secrete a Fluid over Their Adhesive Pads. PLoS ONE 6 (5): e20485. doi: 10.1371/journal.pone.0020485

Abstract
Background. Many arachnids possess adhesive pads on their feet that help them climb smooth surfaces and capture prey. Spider and gecko adhesives have converged on a branched, hairy structure, which theoretically allows them to adhere solely by dry (solid-solid) intermolecular interactions. Indeed, the consensus in the literature is that spiders and their smooth-padded relatives, the solifugids, adhere without the aid of a secretion.
Methodology and Principal Findings. We investigated the adhesive contact zone of living spiders, solifugids and mites using interference reflection microscopy, which allows the detection of thin liquid films. Like insects, all the arachnids we studied left behind hydrophobic fluid footprints on glass (mean refractive index: 1.48–1.50; contact angle: 3.7–11.2°). Fluid was not always secreted continuously, suggesting that pads can function in both wet and dry modes. We measured the attachment forces of single adhesive setae from tarantulas (Grammostola rosea) by attaching them to a bending beam with a known spring constant and filming the resulting deflection. Individual spider setae showed a lower static friction at rest (26%±2.8 SE of the peak friction) than single gecko setae (Thecadactylus rapicauda; 96%±1.7 SE). This may be explained by the fact that spider setae continued to release fluid after isolation from the animal, lubricating the contact zone.
Significance. This finding implies that tarsal secretions occur within all major groups of terrestrial arthropods with adhesive pads. The presence of liquid in an adhesive contact zone has important consequences for attachment performance, improving adhesion to rough surfaces and introducing rate-dependent effects. Our results leave geckos and anoles as the only known representatives of truly dry adhesive pads in nature. Engineers seeking biological inspiration for synthetic adhesives should consider whether model species with fluid secretions are appropriate to their design goals.

 

[BrynWilliams]

thanks zoltan, looks like a good read

also nice that my complete armchair ideas weren't too far off

 

[Jupiterxo]

Hmmmmm...you learn something new every day

 

[pato_chacoana]

Can anyone explain to me the evolutionary selective pressure why terrestrial 'burrowing' species should have such elaborate 'non-slip' structures on the underside of their feet, as i'd be curious to know the answer.

Do tarantulas commonly encounter surfaces like glass in nature? I actually dont think so, sorry, i cant see the selective pressure. The only surface i can think of is waxy leaves, but how often do tarantulas really want or need to walk on such surfaces? Avicularia occasionally perhaps, juveniles of a few arborial species, but thats about it i would think. Few species, rarely. Especially the burrowing species, really, why have such a mechanism to allow them to walk on slippery surfaces when they never encounter such surfaces in nature ??! You generally find a tendency in nature that can be best described as 'use it or loose it'. If a structure or behavor is useless for survival or reproductive success, it generally disappears, which is why for example tarantulas living in dark caves seem to become eyeless. Especially if the structure/behaviour is metabolically costly, as silk production surely is. Even the arboreal species., isn't tree bark really rough enough for them to grip with claws and their more elaborate scopulae?.

Hairs on the tarsi with ducts, ok im convinced. But, what makes these structures silk producing? Why are these not thermosensory setae with open ducts, that exist to detect temperature differences?, i can see why many different tarantulas would benifit from those... silk producing tarsal structures...im not convinced, sorry.

Interesting topic. Stuart, maybe the additional adherence gives burrowers the advantage of better grip when hunting. The additional adherence scopulae can help picking up the preys, hence more chance of feeding. That's one reason I can think of now. Also, certain features remain from past ancestors without an apparent advantage but just passed on ''obligatory'', like if the individual couldn't escape from it, cases where the feature itself doesn't give a benefit or a setback.

Cheers,
Pato

PS: Kirk, please could you send me the paper of the JEB?

 

[pato_chacoana]

Thanks Zoltan!

Cheers,
Pato

 

[Zoltan]

There is a new development in this topic.

Foelix, R. F., B. Rast & A. M. Peattie. 2012. Silk secretion from tarantula feet revisited: alleged spigots are probably chemoreceptors. Journal of Experimental Biology (April 1, 2012) 215, 1084–1089. doi: 10.1242/​jeb.066811

Abstract. Controversial views have been expressed about whether tarantula feet can secrete fine silk threads that could prevent them from falling off smooth vertical surfaces. Two studies have claimed that ‘ribbed hairs’ on the tarsi of tarantulas produce silk. We examined these ribbed hairs in several tarantula species using light and scanning electron microscopy, and compared them with the silk-producing spigots on the abdominal spinnerets. We found that, morphologically, these ribbed hairs correspond very closely to known chemosensitive hairs in spiders; they have a distinct socket, a bent hair shaft with fine cuticular ridges, an eccentric double lumen within the hair shaft, and a blunt tip with a subterminal pore. Spigots on the spinnerets have a large bulbous base instead of a socket, a long shaft with a scaly surface and a central terminal pore. We never observed any silk threads coming out of these ribbed hairs under the electron microscope. By contrast, silk threads exiting the spigots on the spinnerets were common. Interestingly, ribbed hairs also occur on the spinnerets, often side by side with the silk-producing spigots. Our conclusion is that the ribbed hairs are chemoreceptors, not spigots. Observations of live tarantulas clinging inverted to glass coverslips confirmed that some substance is produced by the ribbed hairs, but it remains unclear whether this secretion is actually silk. In any case, the thousands of adhesive setae on the tarsi of legs and pedipalps almost certainly far outweigh any potential contribution from the sparsely distributed trails secreted by the ribbed hairs.

Also, here is an article which basically summarizes the above: http://dx.doi.org/10.1242/​jeb.071597

The DOIs apparently are not working so: http://jeb.biologists.org/content/215/7/1084.short and http://jeb.biologists.org/content/215/7/ii.full

 

[crawltech]

Nice lil read, Zoltan....thanx!

 

[papilio]

Thanks Zoltan! I've recently been looking into this very interesting topic. I had mentioned something about it to Advan, and today he referred me to your latest post. As I see in one of your previous posts, Ts are not considered akin to geckos in having the van der Waals force as the sole mechanism in surface adhesion, and I'm wondering whether you may know what advantage over this force alone might the inclusion of substances as discovered in some Ts' footprints offer?

For anyone who may be interested, as I received no search results for van der Waals, I thought I'd post here a bit of what I've come across on the involvement of this effect in tarantula adhesion. Any corrections in my understanding of what follows are welcome! It is, I believe, quite well established as being the sole mechanism in gecko adhesion, and has been synthesized in the form of very effective dry adhesive pads (easily capable of suspending human weight from smooth surfaces -- this through an effect of quantum mechanics alone).

The structures of setae and of the billions of spatulae covering their tips appear likely to be essentially the same on Ts as they are on geckos. And in watching the TED video referenced below, does the motion of the gecko robot's walk as it peels its toes remind anyone else of the very characteristic 'tarantula walk'? As I watch an adult P. regalis climb up the sides and across the ceiling of its acrylic housing, it appears to plant each foot down squarely, but then as it lifts each leg the movement appears to impart a very slight rolling or 'peeling' action to the foot pads as they're 'unsticking' themselves from the surface. But this bit is just my own observation and conjecture.

While I'm no chemist, for anyone unfamiliar with the van der Waals force my understanding is that it is a quantum mechanical form of molecular attraction and adhesion, having nothing to do with any sort of 'goo', wet or dry, existing between the two surfaces, but is created by the polarity of the molecules themselves in each surface behaving something like electromagnets. When this polarity is not a permanent characteristic of the molecules it's known as induced dipolar interaction, or the London dispersion force (kind of one facet of the van der Waals force). This happens when, as the two surfaces are brought very near each other, a predominance of electrons at the ends of the molecules nearest one surface repels the electrons within the molecules near the other surface and polarity is induced, bringing about a significant attractive force between the two surfaces.

The presence of the nano-structure spatulae covering the tip of each seta increases its suface area (just as corrugated paper has a higher surface area than plain flat paper), resulting in an increase in the attractive force per square unit. This type of adhesion works regardless of the presence of moisture, and functions perfectly well even on molecularly smooth and clean surfaces. I seem to recall reading somewhere that one of the only surface materials which geckos can't climb is teflon sheet! I really need to get some and try it with Ts.

As an aside, it's tempting (as an optical designer) to speculate that it's these very uniform fields of spatulae which give a T's feet that remarkable iridescence. The display of the entire spectum of color as one shifts viewing angle (which can be seen even when viewing the tip of a single seta) is something very rare in nature, occuring also in the feathers of some birds such as peacocks. These act as (among fabricated structures) diffraction gratings, which create by reflection a complete spectrum just as a prism does by refraction (a common example of a diffraction grating would be a CD). In fact the very first diffraction gratings, in Newton's day, were modeled after bird feathers.

Sorry, I hadn't intended to go on at quite such length. But if this is in fact what's going on I find it quite fascinating. And what a mystery it is indeed how/why such a thing evolved, given a T's natural habitat!


http://www.ted.com/talks/lang/en/robert_full_learning_from_the_gecko_s_tail.html
http://www.pnas.org/content/99/19/12252.abstract
http://www.pangeareptile.com/forums...e-Photographs-of-Rhacodactylus-ciliatus-setae
http://www.chemguide.co.uk/atoms/bonding/vdw.html

 

[maxfightmaster]

very interesting! thanks guys.

 

[papilio]

Just ran across this article, mentions studying the van der Waals force in jumping spiders ... to make better post-it notes!

http://www.eurekalert.org/pub_releases/2004-04/iop-smb041504.php

 

[Prometheus]

Tarantulas are just like hobbits... They really are amazing creatures. You can learn all there is to know about their ways in a month, and yet after a hundred years they can still surprise you...