Comments on: Spiders: dimorphic, mimetic, and fluorescent

By: nickybay

nickybay — Tue, 18 Dec 2012 05:31:00 +0000

The 2nd spider is a Theridiid, not an Araneid. Macracantha arcuata (moved from sub-genus of Gasteracantha to it’s own genus almost 20 years ago) does exhibit sexual dimorphism but that spider is not the male.

The 3rd spider is an Araneid, not a Thomisid (crab spider) as described.

Other than scorpions and harvestmen, some millipedes fluoresce under UV light as well, particularly the legs.

By: Rik G

Rik G — Tue, 18 Dec 2012 05:14:22 +0000

It even made the rounds at WEIT!

http://whyevolutionistrue.wordpress.com/2012/01/13/a-golden-cape-of-spider-silk/

By: gravelinspector

gravelinspector — Tue, 18 Dec 2012 02:23:23 +0000

This is a better description of how a quartz wedge works, and the comparison between interference fringes under white light versus monochromatic light.

By: gravelinspector

gravelinspector — Tue, 18 Dec 2012 02:01:45 +0000

My reading of them is that there’s a droplet (air or water – I’m not sure of the medium) with a tapering edge, and it’s giving a “Newton’s Ring” like phenomenon. I’ve done a lot of polarized light microscopy over the years and we’re continually using such effects in, for example, the quartz wedge, the Becke line test, etc. And I’ve seen the same pattern so often on my specs that I’ve never figured any other way of producing the effect. That a “sodium lamp” would produce the effect on my specs where a “white lamp” wouldn’t produce anything noticeable, when viewing a particular raindrop’s meniscus, was a crucial observation in developing my interpretation. (It was so long ago that I had to dredge the memory for a while.) With care, a street lit by sodium lights and “white” lights on passing cars will allow you to select a raindrop and observe it’s meniscus against sodium lamp, white light, back to sodium lamp, back to white light … assuming, of course that you wear specs and that you get rainfall in AridZone? (Not a constraint in Britain!)
Nope, I’m pretty convinced that it’s “Newton’s Rings”.

By: Lou Jost

Lou Jost — Mon, 17 Dec 2012 16:10:07 +0000

Somehow people manage to raise Nephila in commercial quantities, to make golden silk. A cloak or something made of pure Nephila silk was making the rounds in museums a few years ago.

By: Ben Goren

Ben Goren — Mon, 17 Dec 2012 14:19:56 +0000

If you’re referring to the big cyan-colored features in the center on the beastie’s body, I don’t think those’re Newton’s Rings; I think it’s just that there happen to be concentric patterns viewed head-on.

By: Ben Goren

Ben Goren — Mon, 17 Dec 2012 14:16:11 +0000

Actually, the phenomenon you’re seeing isn’t something that could see with UV vision. What’s happening is that the pigment is absorbing high-energy UV light and emitting lower-energy blue light. It’s the same as any other sort of fluorescence.

I don’t know that these animals look like anything special in UV wavelengths…you’d need an actual UV-sensitive camera to tell. Just shining a light with a lot of UV wavelengths in it isn’t going to do the trick, any more than a heat lamp gives you night vision.

Cheers,

By: Diego

Diego — Mon, 17 Dec 2012 12:44:33 +0000

Gasteracantha is one of my favorite spider genera. I used to try and keep G. cancriformes as pets when I was a kid. It didn’t work out well but they lasted longer than the Nephila I tried to do the same thing to, the poor things.

By: Lou Jost

Lou Jost — Mon, 17 Dec 2012 12:40:11 +0000

Alternatively, it might have nothing at all to do with sex. The females are so much bigger than the males that they are surely subject to very different selective pressures. These might be defensive devices or something.

By: Jodie Furner

Jodie Furner — Mon, 17 Dec 2012 11:50:53 +0000

Well, as a lover of all things spider – I am steeling these images!!!