Tarantulas don’t make silk with their feet, according to a new paper which refutes previous research.

In 2006, Stanislav Gorb of the Max Planck Institute for Metals Research in Stuttgart, and his colleagues wrote in Nature that zebra tarantulas (Aphonopelma seemanni) could secrete silk from their feet. This, they argued, helps them climb smooth vertical surfaces and “avoid catastrophic falls”. The finding played well with the media.

Now Fernando Perez-Miles, of the Universidad de la República in Uruguay, and colleagues may have disproved this. They took four zebra tarantulas and used paraffin to seal their spinnerets – the abdominal structures spiders make silk with. After 72 hours they found no silk at all in the containers they were keeping the spiders in, they write in Nature.

They also say that the spinneret structures detailed by Gorb on spiders’ feet are actually sensory structures.

“Tarantulas entangle silk threads from the spinnerets with their tarsi. They often use hind legs to entangle silk, but we also observed A. seemanni entangling with their other legs. This behaviour might explain the presence of the thread footprints photographed by Gorb et al.” write the authors.

However Gorb and his team maintain that spiders may be producing foot-silk. Firstly they argue that the silk in question is laid down in parallel tracks, implying it is not a secondary deposition. Additionally they say that examination of this silk shows a broad area at the beginning of the fibre that could be where it was an initial fluid. If the silk had come from an abdominal organ fluid phases would be lost in transference to the feet, they argue.

“We remain satisfied that the most plausible explanation for our observations is the existence of tarsal-silk-producing structures scattered within the setae on tarantula tarsi,” says their response.

Image: tarantula entangling a silk thread with its hind leg, from Perez-Miles et al.