Theraphosa

Physical description and identification

Theraphosa is a small genus of enormous tarantulas erected by the Swedish arachnologist Tamerlan Thorell in 1870. It contains three species — Theraphosa blondi, the Goliath birdeater; Theraphosa apophysis, the pinkfoot goliath; and Theraphosa stirmi, the burgundy goliath birdeater — and between them they account for the heaviest spiders ever weighed.

Adults

• Size: all three are giants. T. blondi reaches a body length near 12 cm and a leg span of 28–30 cm, with record weights close to 175 g. T. apophysis has a body length around 8–9 cm but a leg span matching or exceeding T. blondi, roughly 25–30 cm; the 9.6 cm leg span quoted in older accounts is far too small and looks like a misapplied body measurement. T. stirmi is marginally smaller but still among the largest spiders alive.
• Colour: all are brown, and colour alone will not separate them. T. blondi runs golden to dark chocolate with faint leg markings, T. stirmi is warmer and more burgundy, and T. apophysis juveniles have distinctly pink tarsi that fade towards maturity.
• Eyes: eight small eyes crowded on a single tubercle at the front of the carapace. These are touch-and-vibration hunters, not visual ones.
• Distinctive features: the fangs are proportionally huge, up to about 2 cm in a large female. The abdomen carries dense Type III urticating setae, and all three species stridulate loudly by rubbing specialised setae on the legs and pedipalps. Adult males are unusual among tarantulas in lacking tibial spurs; T. apophysis males carry a small tibial apophysis that gives the species its name.

Eggs and egg sacs

A female produces one large egg sac containing roughly 50 to 200 eggs, wrapped in thick cream silk and kept in the burrow, where she guards and turns it. The sac as a whole is about the size of a tennis ball; the eggs inside it are small, a distinction older accounts routinely blur. Spiderlings emerge after about six to eight weeks.

Spiderlings

Hatchlings are pale, soft and already large by spider standards. They stay near the mother's burrow briefly, then walk away to dig their own — far too heavy to disperse by ballooning. Growth is slow: several years to maturity, with each stage ending in a moult that also regrows lost legs and replaces spent urticating hairs.

The web and hunting

No Theraphosa builds a snare web. Silk lines a deep burrow, often an enlarged rodent tunnel or a cavity under a root plate, and forms a thin mat with trip lines at the entrance that function as a vibration alarm. Hunting is ambush: the spider waits at the mouth of the tunnel after dark, rushes the prey, pins it and bites. Silk is also used for the moulting bed and the egg sac.

Where Theraphosa tarantulas live

The genus is restricted to the Guiana Shield of northern South America. T. blondi occupies Guyana, Suriname, French Guiana, southern Venezuela and northern Brazil; T. stirmi is known from Guyana and adjacent Brazil; and T. apophysis has a much smaller range in the Venezuelan Amazonas near the tepui country of the upper Orinoco. Accounts that place any of them in North America, or in Africa or Asia, are simply wrong.

Habitat across all three is humid rainforest with diggable ground: swampy margins, marshy hollows, stream banks and the soft soil under fallen timber, where a burrow can be excavated without collapsing and humidity stays high. Burrows run deep and are held for years, and the spiders are strictly nocturnal, which is why they are more often heard than seen.

Are Theraphosa tarantulas venomous?

Yes, as all tarantulas are. The venom is designed for large invertebrates and small vertebrates and is not medically significant to people: there is no antivenom for any theraphosid because none has been needed, and no death is attributable to the genus. Bites cause local pain, redness and swelling that settle on their own.

The urticating hairs are the real hazard, and in Theraphosa they are exceptional. These are Type III setae — stiff, heavily barbed and easily airborne — and a disturbed spider puts thousands into the air at once. On skin the result is an intense itching rash lasting days; inhaled they irritate the airway; in the eye they penetrate the cornea and cause ophthalmia nodosa, needing an ophthalmologist. Old World relatives such as the king baboon tarantula have no urticating hairs at all and rely on much more potent venom instead.

Can Theraphosa tarantulas bite?

They can, but only after a long sequence of warnings. A cornered Theraphosa first tries to retreat into its burrow, then stridulates — a dry rasping hiss audible several metres away — then rears up with fangs exposed, then kicks a cloud of urticating hairs off its abdomen. Biting is the last resort, and a large share of defensive strikes are dry, with no venom delivered.

The injury, when it happens, is mostly mechanical. Fangs up to 2 cm long leave deep punctures that bleed and throb, with local swelling and tenderness for a day or two. Nausea or cramping is occasionally described and necrosis is not a feature of tarantula bites. Wash the wound, apply a cold pack, elevate the limb and use a simple painkiller; seek medical care if redness spreads, pus appears or a fever develops, since infection is the realistic complication. After a hair exposure do not rub the skin — lift the setae off with adhesive tape — and if hairs reach the eyes, get them assessed the same day.

Ecological importance and behavior of Theraphosa tarantulas

Theraphosa species are nocturnal ambush predators and, at their size, apex invertebrates of the forest floor. The diet is dominated by large insects, other spiders and earthworms, with frogs, toads, lizards and small snakes taken regularly and rodents occasionally. Birds are the rare exception that gave the whole group its misleading name; prey is pre-digested externally and a large female can go weeks between meals.

Natural predators: tarantula hawk wasps of the genus Pepsis paralyse adults and seal them in a nest as living food for one larva. Coatis, snakes, large lizards, army ants and birds take exposed or moulting spiders by digging them out, and people in parts of the Guianas and Venezuela roast them as a traditional food.

Prey-predator dynamics: each adult holds a burrow and hunts a small radius around it, so a population applies steady, local pressure on large litter invertebrates and small vertebrates. The burrows themselves are reused by frogs, beetles and other animals, and small frogs have been recorded sheltering unharmed inside occupied tunnels.

Seasonal behaviour: activity peaks with the rains. Mature males abandon their burrows to search for females and rarely live long afterwards, three to six years in total, while females reach 15 to 25 years and keep moulting and breeding for most of it.

Relationship with humans: these spiders are harmless in practice but heavily collected for the exotic-pet trade, where slow growth, exacting humidity needs and airborne hairs make them poor choices for inexperienced keepers. Logging and mining across the Guiana Shield, together with wild collection, are the real pressures on them. Smaller New World species such as the pink toe tarantula and members of Lasiodora are far more common in captivity.

Species in the genus and similar spiders

Quick facts

Did you know?

• All three species stridulate, rubbing setae on the legs and pedipalps to produce a hiss that carries several metres — among the loudest sounds made by any spider.
• The genus is the heaviest, not the longest-legged: the leg-span record belongs to the giant huntsman, while Theraphosa packs far more animal into the same outline.
• Theraphosa stirmi was only recognised in 2008, so many spiders photographed as Goliath birdeaters before then were in fact T. stirmi.
• The "birdeater" name traces to an eighteenth-century engraving by Maria Sibylla Merian showing a large South American tarantula feeding on a hummingbird — a real but exceptional event.
• The species name apophysis refers to a small tibial process on the male, unusual in a genus whose males otherwise lack the mating hooks most tarantulas carry.

In summary, Theraphosa is three species of Guianan rainforest giants that sit at the top of the spider size charts by weight. They hiss, they kick clouds of barbed hairs, and they almost never bite — and the accurate numbers for all three are consistently smaller in body and larger in leg span than popular accounts suggest.