Chaco Golden Knee Tarantula (Grammostola pulchripes)

Physical description and identification

The Chaco golden knee is a bulky, terrestrial tarantula with a simple and reliable field mark: broad golden-yellow to cream bands that ring the joints of all eight legs against a dark brown or near-black base. The common name points at the "knee", the patella, where the band is widest, but the striping usually carries onto the tibia as well.

Adults

• Size: the frequently quoted figure of 20–22 cm is the leg span, not the body. The body itself is a much more modest 6–8 cm long. An adult female is a heavy animal that sits close to the ground; males are similar in span but lighter and longer-legged.
• Colour: carapace and abdomen are dark brown to charcoal, thickly clothed in pale golden, tan or straw-coloured setae. Freshly moulted adults look brightest and dull as the hairs wear. Some individuals show a warmer, pinkish cast to the body hair, which is where the older description of "pink bristles" comes from.
• Eyes: eight small eyes clustered on a raised mound at the front of the carapace. Like all tarantulas it sees poorly and hunts almost entirely by vibration.
• Sexing: mature males carry swollen pedipalp bulbs and a pair of tibial hooks on the front legs, used to brace a female's fangs during mating. Females stay heavier and stockier. Before maturity the only dependable method is examining a shed skin.

Eggs and egg sac

Several weeks after mating the female spins a thick, disc-shaped silk sac deep inside her burrow and fills it with several hundred eggs. She guards it continuously, turning it to keep temperature and moisture even, and defends it more readily than she defends herself. The young emerge roughly six to eight weeks later.

Spiderlings

Hatchlings have a pinkish carapace and a plain brown abdomen with no trace of the adult banding. The gold rings strengthen with each moult until the spider is two or three years old. Growth is slow: females need four to six years to mature, moulting several times a year as juveniles and about once a year as adults. Our page on spider moulting explains why a spider stops feeding and lies on its back beforehand.

The web and hunting

This tarantula builds no capture web. It digs a burrow in firm, dry soil, often against a grass tussock or under a stone, and lines the walls with silk to stop them crumbling. At the entrance it lays a thin silk mat that works purely as a vibration sensor — nothing like the aerial snares described in our guide to spider webs. After dark it waits at the burrow mouth with its front legs on the silk, feels an insect cross, lunges and drags the prey underground.

Where the Chaco golden knee tarantula lives

Grammostola pulchripes is named for the Gran Chaco, the vast dry lowland plain that stretches across Paraguay, northern Argentina and into southeastern Bolivia. The core of the range lies in the Paraguayan Chaco and the Argentine provinces bordering it, and the species has been recorded south into the drier grasslands of central Argentina.

The habitat is open, hot and seasonally very dry: thorn scrub, palm savanna and coarse tussock grassland on sandy or clay soils. This is not rainforest, and the species is not an Amazonian spider. It is strictly terrestrial and fossorial, sheltering by day in a burrow that may be occupied for years and leaving it only at night — or, for mature males, abandoning it altogether during the wandering season.

Its neighbours in southern South America include the jet-black Brazilian black tarantula, the red-abdomened Brazilian redrump, the large Entre Rios tarantula and the Uruguayan black beauty. The genus as a whole is profiled on our Grammostola page.

Are Chaco golden knee tarantulas venomous?

Yes, but harmlessly so for people. Like every tarantula it uses venom to subdue insects, and like other New World terrestrial theraphosids its venom has no documented medical significance for humans. Clinical reviews of tarantula bites record local pain and swelling from this group and nothing systemic: no antivenom exists because none is needed, and no deaths have ever been attributed to a Grammostola species.

The defence that actually matters is not the fangs. As a New World species, G. pulchripes carries a dense patch of urticating hairs on top of the abdomen — barbed bristles it rakes off with a hind leg and throws into the air when alarmed, aimed at the eyes, nose and skin of a mammal leaning over the burrow. Old World tarantulas such as the king baboon tarantula have no such hairs and rely on far more potent venom instead.

Can Chaco golden knee tarantulas bite?

They can, but a bite from this species is genuinely rare. The Chaco golden knee is among the most placid of the large tarantulas: its first response to a disturbance is to back into the burrow, its second is to turn and flick hairs, and biting comes a distant third, usually only when the spider has been pinned or grabbed.

When a bite does occur, the mechanical injury is the larger part of it. The fangs of a full-grown female are close to a centimetre long and strike downward in parallel, so the result is two deep puncture wounds, sharp immediate pain and local swelling that settles over a day or two. The frequent comparison to a bee sting is fair for the venom itself, but understates the puncture. Muscle cramping in the bitten limb has been reported after theraphosid bites in general and is uncomfortable rather than dangerous.

Wash the wound well with soap and water, apply a cold pack, keep the limb raised and take an ordinary painkiller if needed. Seek medical advice if the site becomes hot, spreading and increasingly painful after a day or two, which suggests a secondary skin infection rather than venom; if you develop breathing difficulty, widespread rash or faintness, which would indicate an allergic reaction; or if hairs may have entered an eye. Do not cut, suck or burn the wound.

Ecological importance and behaviour of the Chaco golden knee

In the Chaco this is a long-lived, sit-and-wait predator that exerts steady pressure on the invertebrate community around a single burrow, sometimes for two decades. It hunts at night and takes whatever large arthropods walk within reach: crickets, grasshoppers, beetles, cockroaches, moths and millipedes, with the occasional small lizard or frog. Vertebrates are incidental, not staple food.

Natural predators: ground birds, snakes, lizards, armadillos, coatis and other small carnivorous mammals take adults caught in the open. The specialist enemy is the pompilid spider wasp, which paralyses a tarantula with a sting, drags it into a chamber and lays a single egg on the living body.

Prey–predator dynamics: a female's decades-long tenancy of one burrow makes her a fixed point in the local food web. Very large clutches compensate for extremely heavy mortality among dispersing spiderlings, only a handful of which ever reach a burrow of their own.

Seasonal behaviour: activity peaks in the warm, wetter months. Mature males stop feeding, leave their burrows and wander in search of females, which is when they are most often seen crossing open ground and roads. Females stay put and may reproduce across many seasons.

Relationship with humans: encounters are uncommon because the spider stays underground, and it poses no threat when they happen. Its size and calm temperament have made it one of the most widely kept tarantulas in the world, and captive breeding now supplies most of that demand — which matters for a species that takes half a decade to mature. Habitat loss as Chaco scrub is cleared for agriculture is the larger long-term pressure.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species epithet pulchripes is Latin for "beautiful foot", from pulcher (beautiful) and pes (foot) — a direct reference to the gold-banded legs.
• It was described by the French arachnologist Eugène Simon in 1891, originally in a different genus; the date 1892 appears in some older popular accounts.
• Tarantulas are mygalomorphs, an ancient lineage whose fangs strike straight down in parallel rather than pinching together sideways, which is why they rear up to bite.
• The golden banding is a property of the hair coat, so a freshly moulted spider is at its most vividly marked and fades over the following year.
• A mature male abandons his burrow, stops eating and walks; almost every large "golden knee" found in the open is a male on his final journey.

In summary, the Chaco golden knee is a big, slow, gold-ringed burrowing tarantula of the dry Paraguayan and Argentine lowlands. Its venom is mild and its real defence is a cloud of itchy hairs — read the leg bands and you have identified it.