Tarantulas shoot silk from "spigots" in their feet to climb slippery surfaces, a new study says.
Keeping balance is crucial for the delicate arachnids, which would likely die in a fall. So tarantulas often use silk much like Spider-Man does when wall-crawling—to stick to surfaces and stay firmly attached, even when the ground is shaky, the research confirmed.
Tarantulas don't spin typical spider webs, but often use their silk to line or protect their burrows.
(See "Spider-Man vs. True Spider Superpowers.")
The silk-slinging theory was first put forth in 2006, but scientists have been divided on whether tarantulas shoot silk from their feet, or if they grab silk from their spinnerets—silk-producing organs—and use that as a glue.
To resolve that question, the University of Newcastle's Claire Rind and undergraduate student Luke Birkett put tarantulas into a clean, dry fish tank lined with microscope slides. While filming with a video camera, the team tipped the tank on its side so that the spiders either stayed put or slipped just a bit.
Watching the footage in slow motion revealed that only the spiders' feet had touched the glass, and that the spiders slipped only slightly.
They also examined the slides to look for any evidence of silk secretions, Rind said. "On the slides where the foot was found, we found 20 or 30 silken threads in the footprint."
Spiky Silk Spigots Observed for First Time
Rind also studied tarantula feet under an electron microscope and found tiny silk-producing spigots intermingled with the hairs on the spiders' feet.
Each fuzzy hair looked like a "loo brush," said Rind, while every spigot resembled a "small spike."
Rind saw silk threads still coming out of the spigots—contradicting previous studies that had found that the spikes are sensory structures.
She observed three different species of tarantula under the microscope: the Chilean rose, the Indian ornamental, and the Mexican flame-knee tarantula.
These species are "about as far away as you could get from another on the tarantula tree," so it's likely that all tarantula species possess this silk-slinging ability, Rind said.
(See "Untangling Spiders' Evolutionary Web.")
The Mexican flame-knee tarantula was studied via its molted exoskeleton, which incidentally came from Rind's pet tarantula, Fluffy, who had died before she could participate in the experiments.
But that's OK by Rind: "She was not the best-behaved lady ... a bit aggressive."
The tarantula-silk study will appear June 1 in the journal Journal of Experimental Biology.