Why don't tarantulas get tangled in thier own web?

[CopperInMyVeins]

Now let's do this same test with tokay and related geckos and see how often they loose their grip. My guess is, significantly less than the tarantulas did. This supports the theory that tarantulas have a less powerful mechanism for climbing, and therefore it is unlikely to be van der walls.

Or maybe they just have a less developed use of the force, due to their bristles not being as finely divided? You could do the same test with a sticky pad equipped roach, such as a Madagascan Hissing Cockroach, and it wouldn't fall, that doesn't mean it's using van der waals force, just as falling doesn't mean the spider isn't. As far as I know, tree frogs don't use van der waals force, but they can easily walk upside down on a smooth surface. I've seen a large Rachodactylus leachianus sliding down a verticle plate of glass it was trying to climb, now in that case we know it was using van der waals force, that doesn't mean the force is equally strong in every application, it depends on the structures that are producing it. I'm pretty sure that gecko would fall off an upside down surface a good percentage of the time, by your logic, that would mean it probably doesn't use van der waals. Maybe it just means the structures are not as well developed in Rachodactylus as they are in Tokays.

 

[lucanidae]

Now let's do this same test with tokay and related geckos and see how often they loose their grip. My guess is, significantly less than the tarantulas did. This supports the theory that tarantulas have a less powerful mechanism for climbing, and therefore it is unlikely to be van der walls.

Look, all my testable hypothesis shows is that tarantulas are less able to cling to smooth surfaces. The theory, which is unprovable, but supportable, is that tarantulas don't have the ability to use van der walls force.

Gecko's sliding may be caused by dirty feet, that's in the book you read, or a dirty surface that you simply can not see. Or a genetically deformed gecko, once again, one observation shows nothing.

If tarantulas have such a weak grasp of the van der walls force, then it is most likely not their primary method of climbing. What I think is thier primary method of climbing, is thier claws and hairs grasping inconsistencies in the surface. I've already supported this point.

 

[pronty]

In order for the van der walls force to occur, those hairs would have to subdivide into smaller hair again and again and again, and this is not the case. Looking at SEM pictures of spider and insect tarsi, you just don't see it.

http://www.primidi.com/2004/04/26.html

 

[CopperInMyVeins]

Not always the case, look at Tarantula breeding methods. Seems to me that if some have male hooks and some don't, then some could have different tarsal structures than others. Anything is possible. Look at insect tarsal diversity, it is incredibly diverse. Looks at true spider tarsi versus mygalomorph tarsi, even trap door spiders versus arboreal and terrestrail Theraphosidae.

Yes, I know that many web building true spiders lack tarsal pads completely, because they don't need them, the claws alone allow all the grip they need to walk around on their webs, while non-web building true spiders such as Sparassidae do have tarsal pads, and can climb smooth verticle surfaces (very quickly). On the other hand, every species of Theraphosidae has tarsal pads, don't forget, the same adhesion that allows them to climb verticle surfaces is also what allows them to capture prey so effectively, without it they'd be a big disadvantage.

 

[CopperInMyVeins]

http://www.primidi.com/2004/04/26.html

That came in handy, funny how it's nearly identical, mechanically to the gecko's bristles.

 

[lucanidae]

http://www.primidi.com/2004/04/26.html

This website is excellent in supporting that a species or genus or family or true spiders makes use of the van der walls force. Thank you. But tarantulas are not salticids, and they definetly can not climb or jump as well as they do. Perhaps than, salticids evolved this ability because of a need for it, the ancestors of spiders, and all families of true spiders, definetly do not have this ability

Like I said before, some geckos use van der walls, some don't. Just because salticids do dosen't mean Theraphosids do too.

That came in handy, funny how it's nearly identical, mechanically to the gecko's bristles.

How else would an animal use the van der walls force, of course it's nearly identical to gekcos.

 

[lucanidae]

such as Sparassidae do have tarsal pads, and can climb smooth verticle surfaces (very quickly).

I work with well over 1000 Sparassids. Sometimes, they suddenly become unable to climb glass or plastic anymore, but they can climb metal. It seems that their hairs have become worn down, so they need to grasp a rougher surface. Using the van der walls negates the need for a hair with grapsing ability. Gecko's don't have hairs with grasping ability. Tarantulas have claws that they use primarily to climb. If they are using van der walls, it is not van der walls alone. I stand by tarantulas main ability to climb not being van der walls.

 

[lucanidae]

By the way, this site http://www.primidi.com/2004/04/26.html references Wikipedia, now that is high quality.

 

[lucanidae]

On the other hand, every species of Theraphosidae has tarsal pads, don't forget, the same adhesion that allows them to climb verticle surfaces is also what allows them to capture prey so effectively, without it they'd be a big disadvantage.

Cut the tarsus off the pedipalps, first, and second legs of a tarantula and I'd bet it can still effectively catch prey. They wrap prey quickly into the chelicerae, I don't think they need any stickness to help that quick process.

But let's say that they do. Let's say that you do that and the tarantula can't catch prey. Now find another spider and cut just the tarsal claws off, maybe now it can't catch prey either.

 

[CopperInMyVeins]

Look, all my testable hypothesis shows is that tarantulas are less able to cling to smooth surfaces. The theory, which is unprovable, but supportable, is that tarantulas don't have the ability to use van der walls force.

Gecko's sliding may be caused by dirty feet, that's in the book you read, or a dirty surface that you simply can not see. Or a genetically deformed gecko, once again, one observation shows nothing.

Your theory is based on the opinion that less adhesion means van der waals force is not being used. That is clearly not supported by a gecko also having adhesive problems. Dirty feet? That's just grasping at straws. Both geckos and tarantulas spend most of their lives walking over "dirty" surfaces, their adhesive structures are required to be naturally repellent to interference to remain effective. How useful would a wild gecko's lamella be if dirt suddenly rendered them useless? My tarantulas walk over both moist and dry soil everyday, it has no noticeable affect on their adhesion. Yes, you mention that dirty surfaces are mentioned in the book, so I might as well give you the exact quote: "A gecko can reuse it's bristles thousands of time on any kind of surface - rough, smooth, clean or dirty." Ok, so two of your possible explainations are out, that leaves only a genetically deformed gecko, deformed in such a way that the only noticeable effect is a small reduction in adhesive ability. Seems kind of unlikely, especially since we have no proof that Rachodactylus leachianus usually has more adhesion than that particular animal. On the other hand, my theory is that Rachodactylus leachianus weighs considerably more than a tokay gecko, without a corresponding increase in adhesion, possibly because there aren't as many smooth verticle surfaces in New Caledonia, so it's not needed?

 

[lucanidae]

Ah look, I found what I was looking for:

Dunlop, Jason "Movements of scopulate claw tufts at the tarsus tip of a tarantula spider" Netherlands-Journal-of-Zoology 1995; 45(3-4): 513-520

This article suggests a method of walking for a terrestrial spider based purley on the ability of the claws and hairs to grip into inconsistensies in the substrate.

 

[lucanidae]

Both geckos and tarantulas spend most of their lives walking over "dirty" surfaces, their adhesive structures are required to be naturally repellent to interference to remain effective. How useful would a wild gecko's lamella be if dirt suddenly rendered them useless?

I remember reading that the gecko's have self cleaning hair mechanims, cleans every time they walk. I believe it is in that book. If not, maybe it can be found elsewhere. Meanwhile tarantulas are constantly cleaning their feet. Wait! Look back into the article on Salticids. You don't have to clean off things from van der walls force using mechanisms? Why then are tarantulas always cleaning?

As for that one gecko you saw, all that shows it that the force can be weaker in heavier bodied animals. Ok.... maybe it can also be weaker in different species...fine. But! If it is so week in tarantulas that many can not climb slightly inclined smooth surfaces, than I doubt it is their primary method of locomotion. I refer to the paper I mentioned above which concludes that this terrestrial sp. uses hairs and it's claws to grip into unsmooth surfaces. By your arguments (not mine) this would be the same across all species. By the way, that paper was done on a Grammastola.

 

[CopperInMyVeins]

I work with well over 1000 Sparassids. Sometimes, they suddenly become unable to climb glass or plastic anymore, but they can climb metal. It seems that their hairs have become worn down, so they need to grasp a rougher surface. Using the van der walls negates the need for a hair with grapsing ability. Gecko's don't have hairs with grasping ability. Tarantulas have claws that they use primarily to climb. If they are using van der walls, it is not van der walls alone. I stand by tarantulas main ability to climb not being van der walls.

So, the hairs wear down, and they lose the ability to climb a specific surface, well, if their ability to climb a surface is based on secreting a sticky substance, wouldn't they still be able to secrete it just as well with worn down hairs? Artificial replicas of gecko bristles also quickly wear down, rendering them useless, because the ability to use van der waals force is dependent on the shape of the structure itself. Define "hair with grasping ability" and those without, what structural shapes are you referring to? You make it sound like you think van der waals force is being produced independently of the hairs, when it's actually being produced by the structures of the hairs alone. I'd be interested in seeing a high magnification picture of sparassid hairs, since you have so many on hand. So you can show me which differences in structure define a "hair with grasping ability" that apparently doesn't use van der waals force, compared to spider tarsal hairs that do use it, which have already been shown.

 

[lucanidae]

climb a surface is based on secreting a sticky substance, wouldn't they still be able to secrete it just as well with worn down hairs?

Can't be sure of that. I certainly couldn't pee better if I get into a terrible crushing accident...

Artificial replicas of gecko bristles also quickly wear down, rendering them useless, because the ability to use van der waals force is dependent on the shape of the structure itself.

Replicas, but do the real ones ever? If they do, that's not very evolutionary sound, and a back up method, or different primary method, such as claws that would allow you to cling to rougher surfaces, say metal, would be a big help.

a high magnification picture of sparassid hairs, since you have so many on hand

Damn, you know you can't have everything; I've got the spiders, but no access to an SEM.... how about you get some flordia huntsmen and go stick them under your SEM!!

As for hairs with grapsing ablity, I'd imagine they are curved or hooked. Maybe even strait but as the paper I posted suggests, can be angled and inserted into crevices. What they are not is the densley packed tiny subdived hairs that are pictured in the SEM's of the salticid tarsi discussed ealier. Read the paper I posted, it's short, and fun.

As I've said numerous times now, I don't think the van der walls force is the primary method of clinging/climbing in tarantulas. It may have an effect, it may play a role, but I am not convince they are using it primarily, and neither is the author of the paper I posted. As for my and your understanding of the force itself, perhaps we both need to read more than one coffe table book on the subject.

 

[CopperInMyVeins]

Ah look, I found what I was looking for:

Dunlop, Jason "Movements of scopulate claw tufts at the tarsus tip of a tarantula spider" Netherlands-Journal-of-Zoology 1995; 45(3-4): 513-520

This article suggests a method of walking for a terrestrial spider based purley on the ability of the claws and hairs to grip into inconsistensies in the substrate.

Funny that you should mention an article written in 1995, since at that time the same thing was assumed about geckos, since the limits of microscopy didn't allow the truth to be seen. Remember, all of the gecko research I've discussed as been published in 2000 or later. Before that, everything was speculation, and it was also believed that the number of of bristles alone accounted for the adhesion, or that there was some kind of suction at work. Van der waals force hadn't even been considered in relation to geckos at that point, so why would it have been considered for tarantulas? Now someone has even demonstrated that salticids also take advantage of van der waals force, as opposed to using the insect device of sticky secretions, as previously assumed, do you really think this use is limited to jumping spiders, while other spiders use secretions instead?

 

[lucanidae]

Once again, it wasn't an attack on van der walls, it was a support for another system. As for the limits of microsopy, SEM's were first built in 1965, I'm sure they were doing pretty well by the 1990's. It's not that they couldn't look, they just didn't. And what do you know, they still haven't looked in tarantulas. Instead they found something that DOES work in tarantulas, and it's not van der walls. That paper is not an assumption, its a conclusion. They have found van der walls in spiders, in much more likely candidates, salticids.
Other methods than van der walls for climbing exist in the vertebrate and invertebrate world. Claws is a prevalent one.

And I did not say I am in full support of oily drops, I just presented that as yet another well supported alternative seen in insects. As for other spiders with the lifestyle demands of salticids, they could possibly use the same mechanics. Not many other species jump from leaf to leaf and stem to stem and need the grabbing and sticking power salticids do.

 

[CopperInMyVeins]

I'm sorry, but the argument that claws and grasping hairs are enough to climb a surface such as glass just doesn't do it for me. I'm going to leave it at that for now, on tuesday when I'm back at the museum I'm going to see if I can get access to a SEM and maybe use some tarantula exuvium, since the bristles should still be present. This is definitely something that requires further investigation.

 

[lucanidae]

I'm sorry, but the argument that claws and grasping hairs are enough to climb a surface such as glass just doesn't do it for me.

Awesome, tell that to some Dipterans.

And while you're at it read that paper I sited because that will be crucial for your investigation and you'll need to site it when you publish your finidings.

 

[CopperInMyVeins]

Awesome, tell that to some Dipterans.

Excellent, and while your at it read that paper I sighted because that will be crucial for your investigation and you'll need to site it when you publish your finidings.

I'll definitely read that paper as soon as I can get a hold of it, and I should have specified, it doesn't do it for me when animals of this weight are involved.

 

[lucanidae]

So the van der walls force aids a lot in climbing. This is what geckos and salticids do. But why have it if you don't climb? It is not as though the ancestors of all of these sp. had van der walls capabilities, it evolved, and most definetly seperatly in Gecko's and Salticids. So, maybe terrestrial tarantulas don't have it, because they simply don't need it. But what if they do? How did it get there?

Maybe the starting point is to have hairs that will be shoved into inconsistent surfaces to help in movement. More hairs most likely produces better movement. Natural selection....more and more hairs...and all of a sudden, we have spiders who have such densely packed hairs that they are effected by this force. Definetly plausible. Whether or not this is the case, I'm not sure. I think that terrestrial spiders are much less likely to have evolved more and more densley packed strait hairs over time. Mesothelids, the base group of spiders, don't have these hairs. So the original Theraphosid perhaps needed to evolve a lot of hairs to move around on land, and the van der walls came as a byproduct, thus why the claws still exist. This question is still up in the air.....but the need for van der walls capability in wild terrestrial tarantulas is close to nill.