In what looks to be the last word on the tarantula foot-silk controversy, Fernando Perez-Miles and David Ortiz-Villatoro take a firm stand with the title of their new paper in the Journal of Experimental Biology: "Tarantulas do not shoot silk from their legs." In our last post, we outlined why Rainer Foelix and his team contend that the supposed silk spigots described by research teams supporting the pro-foot-silk position are most likely chemoreceptor hairs. Now, Perez-Miles and Ortiz-Villatoro also dispute the earlier findings of foot-silk; they contend that the silk those researchers found is actually spinneret silk.
Back in 2009, Perez-Miles, Ortiz-Villatoro and two other colleagues challenged the original claim that the zebra tarantula produces foot silk, reporting that when they sealed the tarantula's spinnerets with paraffin before having it cling to vertical pieces of glass, they couldn't find any silk. When yet another team of researchers claimed to have found foot-silk left behind on glass by four different kinds of tarantula, they suggested that the Perez-Miles team might not have shaken the glass enough. In other words, maybe the spiders didn't feel the need to produce foot silk.
Now, Perez-Miles and Ortiz-Villatoro have more closely repeated the procedure of previous foot-silk finders, with four tarantula species. When they left the spinnerets unsealed, they found silk threads in the "footprints" left behind on the glass. When they sealed the spinnerets, they found none. Their conclusion: the footprints became contaminated with spinneret silk, which easily travels from spinneret to leg because it's so light.
In combination with the facts that no one can find silk glands in the spiders' feet and that the "spigots" have more in common with chemoreceptors than with spinneret spigots, this latest piece of research makes it seem highly unlikely that anyone will find spiders whose feet produce silk.