Whether large tarantula spiders are capable of secreting silk from their feet or not has for some years been controversial. A paper from 2006 in the renowned journal Nature appeared to show that tarantulas were able to secrete silk from their feet. However, this claim was refuted in a 2009 paper that found no silk remains from crawling tarantulas when the usual silk secreting spinnerets in the abdomen were sealed. But perhaps the original claim was correct. In a recent issue of the Journal of Experimental Biology, scientists from the University of Newcastle in the UK give evidence of silk secretion from the feet of three different tarantula species.
All modern spiders secrete silk from spinnerets at the underside of their abdomen. All described types of silk such as dragline, web, nest and wrapping silk comes from these spinnerets. However, in 2006, Stanislav Gorb from the Max-Planck Institute in Germany and colleagues discovered silk deposits when they placed a Costa Rican zebra tarantula on microscope glass slides and moved the slides with the spider on towards vertical and concluded that the tarantula can secrete silk from special hairs at their tarsal pads at the end of the legs. The argument is that tarantulas need an extra safety mechanism to prevent falling as these heavy spiders (the Costa Rican zebra tarantula can weigh up to 18 g), unlike their smaller cousins, can be fatally injured from even relatively short falls. Nonetheless, their results were apparently refuted three years later in another study on the same tarantula species by Pérez-Miller and colleagues from Uruguay, who found no silk traces when they sealed the spinnerets on the abdomen of the spider with wax and let the spider move around in a glass-slide covered arena. They concluded that the silk found in the previous study was drawn from the spinnerets by the legs before being placed on the substrate. Now, however, new data in Journal of Experimental Biology suggests that the original study could have been right all along. Claire Rind and colleagues from the University of Newcastle in the United Kingdom repeated the original experiments with the Chilean rose tarantula (Grammastola rosea), but this time also recording the behaviour of the spider to ensure that no contacts where made with the spinnerets during the experiments. They found silk deposits when legs were sliding on the microscope slides. In addition they used scanning electron microscopy to identify potential silk-secreting hairs from the tarsi of a total of three tarantula species (in addition to the Chilean rose tarantula, the Indian ornamental tarantula, Poecilotheria regalis, and the Mexican Flame kneee tarantula, Brachypelma auratum, were used) and found evidence of silk threads extrusions from these special hairs in all species. They conclude that all large tarantulas probably are able to secrete silk from their feet and that the Pérez-Miller study did not find evidence of silk because they used small walls on their arena allowing the spider to partially support its weight on the ground and thus perhaps not causing the legs to slide. However, since Dr Rind and her team did not seal the spinnerets with wax, they did not conclusively proof that the silk could not somehow have come from the spinnerets. Thus only time will tell if the last word has been said on this matter. Sources: Rind FC, Birkett CL, Duncan B-J, Ranken AJ. 2011. Tarantulas cling to smooth vertical surfaces by secreting silk from their feet. Journal of Experimental Biology 214, 1874-1879. Pérez-Miller F, Lucas SM, da Silva PI Jr, Perdomo C. 2009. Silk production from tarantula feet questioned. Nature 461, E9. Gorb SN, Niederegger S, Hayashi CY, Summers AP, Vötsch W, Walther P. Silk-like secretion from tarantula feet. Nature 443, 407.
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