Spiders With Their Heads (and Bodies) in the Sand

The spider’s long legs move frenetically across the sand and pebbles, creating a mini sandstorm of particles that eventually adhere to its body. The spider, in effect, dons a coat of sand that may help protect it from foes and surprise its prey.

It’s a familiar spectacle to Rebecca Duncan, who spent most of her junior and senior years at Lewis & Clark conducting an independent research project using an evolutionary framework to unite biology and physics.

With her research mentors–Greta Binford, assistant professor of biology, and Kellar Autumn, associate professor of biology–Duncan researched the role that hair morphology plays in retaining sand on the surface of spiders. The resulting paper on this work was published in Proceedings of the Royal Society B: Biological Sciences and highlighted in the premier journal Nature.

Application of this discovery could lead to improved designs for materials used in military camouflage and air filtration systems, for example, or even in household dusting tools.

“It was exciting to take on my own question and find my own answer,” Duncan says. “As an undergraduate, I had the opportunity to put into practice everything I had learned in the classroom and lab about conducting good research.”

The two spiders in question–Sicarius and Homalonychus–exhibit entertaining but vital behaviors for collecting sand on their surface such as kicking sand on their bodies or rolling around on their backs in sand.

While previous studies had suggested that fine particles associate with the dense hairs covering these spiders, none had proposed how this occurs or asked if the hair structure plays a role. Through high-resolution imaging, Duncan discovered that both unrelated spider genera had microscopic fibers (“hairlettes”) extending from the shaft of the main hairs that adhere to sand particles.

By determining that sand sticks better to hairs with hairlettes than to those without, Duncan concluded that the presence of tiny hairlettes in two unrelated sand-covering spiders had evolved independently as adaptations, allowing the animals to perfectly match the color of their native environment.

“The sand trapping hairs on the spiders are a physical phenomenon, but we looked at the problem of how sand sticks to spiders from an evolutionary perspective, which helped us come to our conclusion,” Duncan says. “I think this paper is a beautiful example of how approaching questions across scientific disciplines from an evolutionary angle can lead to insightful discoveries.”

Currently, Duncan is working as a research technician in Binford’s lab, helping to mentor undergraduates and managing a large collection of spiders as she continues to gather and analyze data. She plans to attend graduate school.

Binford stresses that Duncan’s scientific leadership and initiative is just as important as her breakthrough research.

“Rebecca accomplished something very rare among undergraduate students,” Binford says. “The caliber of her work easily stacks up to doctoral research projects, and to be published in such a prestigious journal this early in her career is phenomenal.”

–by Jodi Heintz and Pattie Pace