Silk production from tarantula feet questioned

SUMMARYLike all spiders, tarantulas (family Theraphosidae) synthesize silk in specialized glands and extrude it from spinnerets on their abdomen. In one species of large tarantula, Aphonopelma seemanni, it has been suggested that silk can also be secreted from the tarsi but this claim was later refuted. We provide evidence of silk secretion directly from spigots (nozzles) on the tarsi of three distantly related tarantula species: the Chilean rose, Grammostola rosea; the Indian ornamental, Poecilotheria regalis; and the Mexican flame knee, Brachypelma auratum, suggesting tarsal silk secretion is widespread among tarantulas. We demonstrate that multiple strands of silk are produced as a footprint when the spider begins to slip down a smooth vertical surface. The nozzle-like setae on the tarsi responsible for silk deposition have shanks reinforced by cuticular thickenings, which serve to prevent the shanks' internal collapse while still maintaining their flexibility. This is important as the spigots occur on the ventral surface of the tarsus, projecting beyond the finely divided setae of the dry attachment pads. We also reveal the structure and disposition of the silk-secreting spigots on the abdominal spinnerets of the three tarantula species and find they are very similar to those from the earliest known proto-spider spinneret from the Devonian period, giving another indication that silk secretion in tarantulas is close to the ancestral condition.

Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Tarantulas cling to smooth vertical surfaces by secreting silk from their feet

Rind

Birkett

Duncan

et al. 2011

“…In all eight spiders of the four species with sealed spinnerets, no traces of silk were found, confirming the results of Pérez-Miles et al (Pérez-Miles et al, 2009) in A. seemanni. The explanation by Rind et al (Rind et al, 2011) as to why silk was absent in our previous study (Pérez-Miles et al, 2009) is not applicable here because we used larger vertical surfaces and also induced the tarantulas to slip.…”

Section: Discussionsupporting

confidence: 81%

“…Pérez-Miles et al (Pérez-Miles et al, 2009) tested the same species walking on vertical and horizontal glass surfaces. When the spinnerets were sealed with paraffin, no silk was found.…”

Section: Introductionmentioning

confidence: 99%

Tarantulas do not shoot silk from their legs: experimental evidence in four species of New World tarantulas

Pérez‐Miles¹,

Ortíz-Villatoro²

2012

Self Cite

SUMMARY Theraphosid tarantulas, like all other spiders, secrete silk from spigots on the abdominal spinnerets. A few years ago, it was proposed that the large tarantula Aphonopelma seemanni could extrude silk from specialized spigots on the tarsi to help adhesion to vertical surfaces. This suggestion was later questioned because silk was not observed after the spinnerets had been sealed. Recently, experiments with the tarantula Grammostola rosea again suggested tarsal silk secretion. All observations of the supposed tarsal silk were made in spiders with functional spinnerets, thus contamination with silk coming from the spinnerets could not be excluded. Recent morphological arguments also questioned putative tarsal spigots and proposed that they are actually contact chemoreceptors. We here test the supposed tarsal silk secretion in Aphonopelma seemanni, Avicularia avicularia, Brachypelma vagans and Grammostola mollicoma using similar experimental conditions as the previous authors, but with sealed spinnerets. Our results clearly demonstrate that when spinnerets are sealed, tarantulas do not show any tarsal silk secretion. We reinterpret those putative tarsal spigots and discuss possible evolutionary implications of these findings.

“…This claim was challenged in a subsequent study by Pérez-Miles et al (Pérez-Miles et al, 2009), who observed that tarantulas with sealed spinnerets did not produce any silken threads on vertical glass walls. The implication was that silk traces found within the tarantula's footprints originated from the abdominal spinnerets and not from presumed tarsal silk glands.…”

Section: Introductionmentioning

confidence: 92%

Silk secretion from tarantula feet revisited: alleged spigots are probably chemoreceptors

Foelix

Rast

Peattie

2012

SUMMARYControversial views have been expressed about whether tarantula feet can secrete fine silk threads that could prevent them from falling off smooth vertical surfaces. Two studies have claimed that ʻribbed hairsʼ on the tarsi of tarantulas produce silk. We examined these ribbed hairs in several tarantula species using light and scanning electron microscopy, and compared them with the silk-producing spigots on the abdominal spinnerets. We found that, morphologically, these ribbed hairs correspond very closely to known chemosensitive hairs in spiders; they have a distinct socket, a bent hair shaft with fine cuticular ridges, an eccentric double lumen within the hair shaft, and a blunt tip with a subterminal pore. Spigots on the spinnerets have a large bulbous base instead of a socket, a long shaft with a scaly surface and a central terminal pore. We never observed any silk threads coming out of these ribbed hairs under the electron microscope. By contrast, silk threads exiting the spigots on the spinnerets were common. Interestingly, ribbed hairs also occur on the spinnerets, often side by side with the silk-producing spigots. Our conclusion is that the ribbed hairs are chemoreceptors, not spigots. Observations of live tarantulas clinging inverted to glass coverslips confirmed that some substance is produced by the ribbed hairs, but it remains unclear whether this secretion is actually silk. In any case, the thousands of adhesive setae on the tarsi of legs and pedipalps almost certainly far outweigh any potential contribution from the sparsely distributed trails secreted by the ribbed hairs.