Hexophthalma

Physical description and identification

Hexophthalma is a small genus of flattened, six-eyed spiders in the family Sicariidae, confined to the arid parts of southern Africa. Eight species are currently recognised: H. albospinosa, H. binfordae, H. damarensis, H. dolichocephala, H. goanikontesensis, H. hahni, H. leroyi and H. spatulata. The best known by far is the six-eyed sand spider, H. hahni, which supplies almost every photograph attached to the genus.

Sicariidae holds three genera: Loxosceles, the worldwide recluses; Sicarius, the sand spiders of the Americas; and Hexophthalma, their African counterpart. All three share the six-eyed pattern and the same venom enzymes, but only the sand spiders bury themselves.

Adults

• Size: body length runs from roughly 8 mm in the smaller species to around 20 mm in large females, with leg spans of 30–50 mm. Males are smaller-bodied and longer-legged than females.
• Colour: reddish brown, yellow-brown, grey or pale ochre. Colour tracks the local sand closely, and the grains stuck to the body make the underlying shade hard to judge in the field.
• Eyes: six, in three well-separated pairs — the family character, and the quickest way to place any sicariid. Our guide to spider eyes sets it against the eight-eyed arrangements found in most other families.
• Distinctive features: a strongly flattened body, laterigrade (sideways) legs, and a dense covering of barbed bristles that hold sand grains. Species-level identification needs an adult specimen and a microscope, because the differences lie in the genitalia rather than in colour.

Eggs and egg sacs

Females produce flattened, disc-shaped sacs of white silk and bury them in the substrate rather than suspending them in a retreat. Buried sacs pick up a crust of sand within hours and become effectively invisible, which is why so little has been published about clutch sizes.

Spiderlings

Spiderlings leave the sac pale and translucent and take up the adult burying behaviour almost immediately. Development is very slow, several years to maturity being normal for the group, and juveniles moult repeatedly along the way, as described in our guide to spider molting.

No web, only ambush

No Hexophthalma species builds a capture web. Silk is limited to the egg sac and short drag lines. The spider settles onto loose sand, flicks grains over its back with its legs until only the front of the carapace shows, and waits for prey to walk within reach. Vibration through the sand is the trigger; the strike comes upward and is over in an instant.

Where Hexophthalma spiders live

The genus is endemic to southern Africa, and the claim found in many older sources that it is a South African genus is too narrow. The centre of diversity is Namibia, particularly the Namib Desert and the dry river valleys that cut through it; several species are known only from there. The genus also occurs across the arid west and north of South Africa — the Northern Cape, the Kalahari margins and the drier parts of the Western Cape — and extends into Botswana and southern Angola.

Habitat requirements are consistent across the genus: loose, dry, wind-worked sand with something overhead. Collectors find them under rock overhangs and boulders, at the base of desert shrubs, under dead wood in dry riverbeds and in the soft floors of shallow caves. None of the species is associated with buildings.

Are Hexophthalma spiders venomous?

Yes. All members of the genus carry venom containing sphingomyelinase D, the dermonecrotic enzyme that gives Sicariidae its medical reputation and that is also present in the recluse spiders. Laboratory studies of Hexophthalma venom, mainly rabbit-model experiments on H. hahni carried out in southern Africa, showed potent cytotoxic activity: destruction of red blood cells and severe local tissue damage, in some assays at lower doses than Loxosceles venom required for a comparable lesion.

That is the laboratory picture, and it should not be reported as a clinical one. Confirmed human envenomations by any Hexophthalma species are extremely rare; the handful of suspected southern African cases on record are not supported by an identified spider. No antivenom exists for the genus, and recluse antivenoms have not been validated against it. Popular lists of the most venomous spiders rank these spiders highly on venom potency alone — a measure of what the venom does in an assay, not of how often anybody is bitten.

Can Hexophthalma spiders bite?

They can, but records of it happening are almost nonexistent. These are slow, retiring animals whose response to any disturbance is to scuttle sideways and bury themselves. They do not rear, do not defend a web and have no reason to approach a person. A bite would require the spider to be pressed against skin — a hand placed on sand it was under, or an individual trapped in a boot, glove or bedroll.

Because no properly documented case series exists, no reliable clinical description of a Hexophthalma bite can be given. Venom chemistry predicts a course resembling severe loxoscelism: minimal pain at first, then pain and swelling over several hours, a lesion that may enlarge and darken over days, and a real risk of red-cell breakdown. Anyone who believes they have been bitten should wash the site with soap and water, apply a cold pack, keep the limb still and elevated, and get to hospital promptly, bringing the spider or a photograph if it can be collected safely. Cutting, suction, heat and folk remedies make wounds worse and remove no venom.

Ecological importance and behavior of Hexophthalma spiders

Across the genus the lifestyle is the same: buried ambush predation in hot, dry, sandy country. The spider lies beneath the surface with only the eye region exposed, reads approaching prey as vibration in the sand, and strikes upward. Recorded prey includes beetles and beetle larvae, termites, ants, solifuges and scorpions — the hard-bodied, ground-active arthropods that dominate desert nights.

Natural predators: the published record is sparse, unsurprisingly for an animal that is effectively invisible. The plausible predators are those that dig or probe sand: parasitoid wasps, scorpions, solifuges, desert lizards, ground-feeding birds and small insectivorous mammals. Burial is the genus's answer to all of them.

Prey-predator dynamics: by taking large, well-armoured prey including scorpions, these spiders occupy a predatory position few other desert spiders can. Densities and metabolic rates are low, so their influence is persistent rather than sudden.

Longevity and seasonal behavior: sicariids are long-lived. Captive sand spiders of this group have been kept for well over ten years and tolerate long fasts, taking their water from prey — figures that fit the wider picture in our guide to how long spiders live. Activity follows temperature rather than season, with movement in the cooler hours and deeper burial during the heat of the day.

Relationship with humans: negligible. The genus does not colonise buildings, is rarely seen even by residents of its range, and has no pest status. Gloves when moving rocks and dead wood, and a shake-out of boots and bedding, cover the risk.

Species in the genus and similar spiders

Quick facts

Did you know?

• The genus was named twice by the same man. Ferdinand Karsch erected Hexomma in 1878 for a single species, then discovered the name was already taken by a harvestman and replaced it with Hexophthalma in 1879.
• Between 1900 and 2017 nearly all African material was placed in the American genus Sicarius. A phylogenetic study of the family showed that arrangement made Sicarius unnatural, and Hexophthalma was brought back for the African species.
• Hexophthalma binfordae honours Greta Binford, the arachnologist whose work traced the evolution of sphingomyelinase D across sicariid venoms.
• Hexophthalma goanikontesensis is named after Goanikontes in the Swakop River valley of Namibia, and several of its relatives are similarly known from single Namibian localities.
• The genus name simply means six eyes — exactly the character that identifies a sicariid in the field.

In summary, Hexophthalma is a small, strictly southern African genus of buried sand hunters with a scientific reputation far larger than its footprint. Their venom is potently cytotoxic in laboratory studies, confirmed human envenomations are extremely rare, and the six-eyed sand spider is the only species most people will ever hear about.