Feet Colouration

Whaagh

Arachnosquire
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Jun 5, 2013
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Hi Guys

I have a bit of a Tarantula Physiology question, On a lot of your old world and some new world Species they have this blueish/greenish tint on the bottom of their front feet/pedipalps. Do you guys know of any reason for this or is it a warning. Here is a example:

 

assidreemz

Arachnosquire
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Sep 10, 2014
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I'd say it either ties into the whole, "bright colors=poisonous/dangerous", "threat pose",
Or it is a bi product of whatever it is that composed that section of leg for whatever reason for whatever purpose...
Haha, just my 2¢
 

klawfran3

Arachnolord
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"All eight feet bear a tarsal scopula, which is equipped with setae, these again being covered by numerous setules. they are used for friction and adhesion on smooth surfaces. Adhesion to the substrate does not depend on the secretion of an adhesive fluid. Analysis via atomic force microscopy (AFM) shows that a single setule can produce an adhesive force (Fa) of 38.12·nN perpendicular to a surface."
(A. B. Kesel*, A. Martin and T. Seidl, 2003)
They seem to reflect a lot of light and I believe they give off the blue-green tint you see on the many different genera.


note on the paper I quoted, it's based off of a jumping spider, but tarantulas have them too.

Read the paper! it's pretty cool
 

Poec54

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Vivid and contrasting colors and markings are used for warnings to predators and intruders. I think every tarantula I've ever seen has iridescent scopula. Only an blind person couldn't get the message that OBT is sending: 'Approach at your own peril.'
 

z32upgrader

Arachnobaron
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The iridescence is a product of the very dense setules on the scopulae. This actually splits the light into its colors like a prism. It gives the spider the ability to adhere to smooth surfaces and grip objects it touches with virtually no effort, like tongs lol. Here's a picture I just took of my S. calceatum's molt at 60x and it's pretty clear what's going on.
Photo Jan 30, 11 10 35 AM.jpg

The angle at which the light source is directed at the scopulae determines what colors you see. I had the light hitting from around 90°, and it looked like this. When I rotated the light source to closer to 270-300°, it changes to green/yellow.
 
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Poec54

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The iridescence is a product of the very dense setules on the scopulae. This actually splits the light into it's colors like a prism. It gives the spider the ability to adhere to smooth surfaces and grip objects it touches with virtually no effort, like tongs lol. Here's a picture I just took of my S. calceatum's molt at 60x and it's pretty clear what's going on.

The angle at which the light source is directed at the scopulae determines what colors you see. I had the light hitting from around 90°, and it looked like this. When I rotated the light source to closer to 270-300°, it changes to green/yellow.
Great pic! Tarantulas would have first developed scopula for climbing, and colors probably came later. With their fang arrangement, which requires stabbing downwards, colors are a nice evolutionary 'add-on' when standing up in a threat display trying to make a warning as dramatic as possible. Red around the mouths parts adds to it. One of the most impressive displays in the tarantula family is the black and yellow ventral leg bands on Poecs, using the warning colors/stripes of bees. Black/yellow bands, alternating colors of blue and green on the scopula when they move, red mouthparts, and fangs extended. Wow. If that doesn't stop your advance, don't expect any mercy. You deserve what you get.
 

Sana

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This is a really interesting and informative thread. Thank you all for taking the time to teach this to those that are still learning!
 

miss moxie

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I would also assume that when walking around, it would flash every time they lifted their feet. Another warning to help dissuade predators from approaching so the spider doesn't have to flip into threat pose.
 

Poec54

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This is a really interesting and informative thread. Thank you all for taking the time to teach this to those that are still learning!
There are so many fascinating things about tarantulas, it'll take decades to figure out a lot of them. How did they ever come up with digesting prey before swallowing it? Or using a secondary device (pedipalps) for sperm delivery? How did that come about? They're covered in sensory organs, the uses for silk are incredible. What advantages silk gives them! Stronger than steel, and yet super flexible.
 

klawfran3

Arachnolord
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The book "biology of spiders" has a great segment on these scopula pads. I really don't feel like typing it all out right now, but the basic gist of is is that the bristles have little hairs on them which have even smaller outcroppings on THEM, allowing more surface area and thus causing capillary action from water in the substrate. This tension allows the spider to walk upside down even on glass for smaller species. According to one study, on substrates without any water occurring on it (Teflon was used I believe) the spiders would slip and slide off, showing that it mostly relies on the capillary action and not friction. The hairs also occur on the inside of the main bristle facing the body so that it doesn't catch on the substrate when it drags it along the ground.
It's really interesting stuff actually. Reading the book seriously changed the way I view ALL spiders and not just tarantulas. Little miracles of nature they are.
 
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