Six-Eyed Sand Spider

Sicarius hahni — the six-eyed sand spider — is one of about 21 species in family Sicariidae (the six-eyed sand spiders and their relatives — including the six-eyed sand spiders Sicarius and the recluse spiders Loxosceles, both of which produce SPHINGOMYELINASE-D in their venom). The species is found in the deserts of southern Africa (especially Namibia, southern Botswana, and the Northern Cape of South Africa). Females are 8-15 mm body length, with the species' diagnostic features: only SIX EYES (instead of the typical eight eyes in most spiders — six-eyed eye arrangement is shared with sister genus Loxosceles, the recluse spiders), tan-brown body coloration that matches desert sand, and short flattened legs adapted for burrowing in sand. The species is famous for the EXTREME AMBUSH PREDATION strategy — six-eyed sand spiders BURY THEMSELVES in loose desert sand, with only the EYES EXPOSED at the surface, and wait motionless for prey (small arthropods, lizards, etc.) to walk over the sand surface. When prey is detected (typically by vibrations transmitted through the sand), the spider lunges out of the sand to seize the prey with the chelicerae and inject venom. The species' VENOM is one of the MOST POTENT SPIDER VENOMS on Earth. Laboratory studies by Newlands and Atkinson (1988, South African Medical Journal) showed that drop-for-drop, the species' venom contains the most toxic spider venom yet measured TO VERTEBRATE ANIMALS — rabbits injected with extracted venom showed ACUTE THROMBOTIC-HEMORRHAGIC SYNDROME with massive necrosis at injection sites, similar to (but more severe than) the brown recluse necrotic syndrome (the recluse spider venom contains the same SPHINGOMYELINASE-D enzyme as Sicarius venom, but at lower concentrations). The active toxin (sphingomyelinase D) attacks vertebrate cell membranes, breaking down the membrane lipid sphingomyelin and triggering cascading damage to red blood cells, vascular endothelium, and surrounding tissues. Despite the extraordinary venom potency, the species RARELY BITES HUMANS — six-eyed sand spiders are EXTREMELY SHY and retreat deeper into the sand burrow when disturbed, rather than attacking. There is no documented human fatality from a six-eyed sand spider bite, and no commercial anti-venom is produced because bites are so rare. The species is one of the most-Googled and most-mythologized spiders on Earth (despite the very low actual human risk) because of the extraordinary venom potency. The species is featured in essentially every modern textbook discussion of spider venom potency.