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Foot Silk: True or False?

Last summer, a team of researchers reported they had indeed found that tarantulas secrete silk from their feet. This appeared to settle a controversy that had started in 2006 when a different team reported finding foot silk. The original finding was bound to be controversial: no one had ever before observed the secretion of silk from the feet of any kind of spider. In 2009, a team investigating the first claim couldn't find evidence of foot silk. Last summer's report, which included a micrograph that seemed to show a blob of silk protein forming at the tip of a purported foot silk spigot, appeared to validate the 2006 report. (For a discussion of these three reports and of the questions concerning silk evolution they raise, see this earlier Spider Silk blog post.)

Well, there is now more evidence that tarantulas actually DON'T produce foot silk. Rainer Foelix is a leading spider anatomist and author of the must-have Biology of Spiders. When he examined the micrographs included in last summer's report, the alleged foot silk spigots looked like chemoreceptor hairs he had studied intensively in the 1970s. Kathryn Knight summarizes what Foelix did next. He, Bastian Rast, and Anne M. Peattie report their full findings in the April 1, 2012, issue of the Journal of Experimental Biology.

Foelix, Rast, and Peattie explicity address the questions concerning silk evolution that these earlier studies raised for us. They note that--even if the silk allegedly secreted through the foot "spigots" really is silk--all the tarantulas tested tend to stay close to the ground. It's not clear, then, what survival advantage foot silk would give them, particularly when the tiny amounts produced would add little cling compared to the spiders' already clingy adhesive setae, or hairs.

Most interesting to us, the team compared the feet of the tarantulas in their study to the feet of Liphistius desultor, a mesothele. As readers of Spider Silk know, mesotheles make up the oldest extant branch of the spider family tree. They live in burrows, rarely venturing more than a few inches beyond the burrow's trap door. Foelix, Rast, and Peattie state that Liphistius has no adhesive hairs on its feet. But it does have the same hairs that earlier researchers identified as silk spigots but that Foelix et al. are pretty convinced are chemoreceptors. The tiny amounts of "silk" produced from the hairs in question wouldn't allow the mesotheles to climb, even if they wanted to.

Next step in deciding whether the hairs in question on tarantula feet are silk spigots or chemoreceptors: testing them for sensory innervation with transmission electron micrography. Down the road, we wonder whether anyone will find any evolutionary connection at all--given the evolutionary relationship between limbs and spinnerets--between the proteinaceous fluid that apparently oozes from these hairs (which are also found on the spinnerets and all extremities) and the protein silk that is secreted through spinneret spigots.

As usual, the best research leads to more questions.  Read More 
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Darwin Day 2012

Happy Darwin Day!

If you google "darwin day" on blogs, you'll find a variety of science and other writers' personal appreciations of Darwin's genius--highly recommended. Here, we're of course partial to spiders. Darwin was more of a beetle man, but if you follow this link to last year's Darwin Day post, you can read of his noteworthy encounter with spider silk. Read More 
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Photographing



A neat little video from a couple of years ago that we somehow missed. Jonathan Coddington is one of the world's foremost arachnologists, and here he explains how photography gives today's araneologists an advantage over araneologists of the past. One quibble: Despite what Jonathan says, flying insects often do see webs. Why they still fly into them is a big research question we discuss in Chapter 10 of Spider Silk, "Now You See It, Now You Don't." Thanks to Bug Girl for bringing this video to our attention. Read More 
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Skeptically Speaking Spider Silk Podcast…

…is now available here. It was great fun talking with host Desiree Schell. The episode begins with an interesting conversation with Ed Yong about recent research resulting in hybrid spider-silkworm silk.
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Spinnerets

Walter Piorkowski has some amazing--and surprisingly beautiful--photomicrographic images of spider spinnerets at Photomacrography.net here and here and here. Walt, if you happen to see this, please let us know what species you were looking at and anything else you would like us to know--I'm not having much luck trying to contact you. Thanks for this unusual look at the external features of the silk system. Read More 
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Spider Silk on Skeptically Speaking

I'll be interviewed tomorrow night, Sunday January 8th, 6PM Mountain Time, on Skeptically Speaking. Please click on the link for details and instructions on how to submit questions. Should be fun!
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Silkworms and Spider Genes

If you don't already follow Ed Yong's great Not Exactly Rocket Science, you've been missing some of the best science blogging around. Check out his latest post, on research involving the insertion of spider silk genes into the genome of silkworms. These silkworms produced silk that's an improvement (in human terms; silkworm silk works just fine for silkworms) over normal silkworm silk, but not really up to spider dragline silk standards. There are all sorts of possible reasons for this result; I give some of them in the comments section below the post.  Read More 
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Inspiring

Silk was one of the first fibrous proteins to be investigated in the early 20th century. Spider silk's exceptional properties have long inspired researchers from fields ranging from mechanical engineering to biotech. Now three MIT researchers from the Departments of Mathematics and Civil and Environmental Engineering have used a new concept called ontology logs, from the category theory branch of mathematics, to examine the relationship between spider silk's structure and function.

The really different aspect of this research? They conducted their examination by comparing spider silk and classical music. And they present their findings as a demonstration of a new way of gaining insight into various structures built on smaller and smaller substructures. Read more at MITnews.

The original paper, by Tristan Giesa, David I. Spivak, and Markus J. Buehler, is published in BioNanoScience. Read More 
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Deterring

Shichang Zhang and colleagues have found that at least one orb weaver, Nephila antipodiana, deposits a substance on its web threads that deters ants. Ants prey on spiders, but ants have not often been seen preying on orb weaving spiders. Zhang et al. may have discovered why.

Alex Wild, over at Myrmecos, has a good summary of the study as well as an interesting quibble about the range of ants tested.  Read More 
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Spider Silk on Word of Mouth

Virginia Prescott of New Hampshire Public Radio's Word of Mouth program had some great questions about spiders and spider silk this Halloween. You can listen in here.
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