Sicarius

Natural History

Sicarius are ground-dwelling species and occur in dry forests and deserts throughout Southern Africa, South America and Central America.  They do not spin webs as retreats or for prey capture.  Instead, they bury themselves in a layer of soil where they live and wait to ambush prey.  During self-burial, soil particles adhere to the thousands of tiny, specialized setae (hairs) covering their bodies and cover the spider, transforming it's natural coloration to the color of the environment.  Sand-covering is thought to be a form of camouflage for these spiders.

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Left: A Sicarius in the field in Argentina, covered in sand. © 2004 Greta Binford. Right: Thousands of microscopic setae, or hairs, cover Sicarius. © 2005 Greta Binford.

The setae covering Sicarius possess long, nanometers thin "hairlettes" protruding from them that have been observed to adhere directly to particles under a scanning electron microscope.  Mathematical models suggest that particles of the size range that stick to Sicarius are able to adhere to hairlettes via weak molecular forces, such as van Der Waals.  Hairlettes are thought to be an adaptation conferring sand adhesion in Sicarius since an identical setal morphology has evolved independently in the Entelegyne spider genus Homalonychus, which also cover their bodies in dry soil particles, and particles fail to adhere as densely to the bodies of related genera that lack hairlettes.

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Left: Particles adhere to the setae covering the exoskeleton of Sicarius.  Right: Sicarius setae have long, thin hairlettes protruding from them that adhere directly to particles, perhaps by intermolecular forces. © 2005 Greta Binford.

Other Names for Sicarius

• Vernacular Names: Six-eyed sand spiders

References

Binford, G.J., Callahan, M.S., Bodner, M.R., Rynerson, M.R., Berea Núñez, P., Ellison, C.E., Duncan, R.P. 2008. Phylogenetic relationships of Loxosceles and Sicarius spiders are consistent with Western Gondwanan vicariance. Molecular Phylogenetics and Evolution 49:538-553.

Duncan, R.P., Autumn, K., Binford, G.J., 2007. Convergent setal morphology in sandcovering spiders suggests a design principle for particle capture. Proceedings of the Royal Society B: Biological Sciences 274 (1629), 3049–3056.

Information on the Internet

• Six-eyed sand spider lunges for lunch. Oregon Public Broadcasting video footage of Sicarius burying themselves in sand and catching prey.