Grammostola

Physical description and identification

Grammostola is a genus of large, ground-living tarantulas in the family Theraphosidae, subfamily Theraphosinae, infraorder Mygalomorphae. Eugène Simon erected it in 1892, and about twenty species are currently recognised, every one of them South American. Four dominate what most people see of the genus: the rose hair (G. rosea), Grammostola porteri, the Brazilian black (G. pulchra) and the Chaco golden knee (G. pulchripes).

Adults

• Size: the figure of 7–9 inches quoted for this genus is a leg span, not a body length, and the distinction matters. Adult females have a body length of roughly 5–7 cm and a leg span commonly between 13 and 20 cm (5–8 in); G. pulchripes is among the largest and can exceed that. Males mature smaller, lighter and longer-legged.
• Colour: most species are some shade of brown to near-black, overlaid with copper, orange-red or pink bristles that give the carapace and abdomen a warm sheen in sunlight. G. pulchra is the exception — a uniform, glossy jet black.
• Eyes: eight small eyes packed on a low tubercle at the front of the carapace. Vision is negligible; these are touch-and-vibration animals.
• Distinctive features: a stout, hairy build with thick legs, a pair of fangs that strike downwards, and a patch of urticating setae on the upper abdomen. Mature males lose the bulk, gain long legs, and carry hooks on the front legs used to lock a female's fangs during mating.

Eggs and egg sac

A female lays her eggs on a silk mat inside the burrow and folds it into a sac she turns and guards for weeks. Clutches are large — a few hundred eggs is normal and around 500 is often quoted — and she frequently lines the sac with urticating hairs plucked from her own abdomen.

Spiderlings

Spiderlings emerge small, pale and already independent, disperse on foot, and dig their own scrapes within days. Growth is slow even by tarantula standards: a Grammostola may take four to six years and a long series of molts to mature, which is part of why the adults live so long.

The burrow and hunting

No Grammostola builds a web to catch prey — but the claim that they "do not make webs" is too broad. Silk is central to the animal's life: it lines the burrow wall, forms a mat at the entrance that registers footsteps, carpets the floor as a molting bed, and males spin a small sperm web before mating. Many species dig, while others, G. rosea among them, simply take over a crevice under a rock or a rodent burrow and silk it shut. Hunting is pure ambush: the spider sits at the mouth after dark, feels a beetle cross the silk, lunges, and drags the prey underground.

Where Grammostola tarantulas live

The genus is confined to South America, and specifically to the cone of the continent south and west of the Amazon basin: Argentina, Uruguay, Paraguay, southern and eastern Brazil, Bolivia and Chile. Peru is sometimes listed in popular accounts, but it is not part of the established range of the genus.

Habitat follows a clear pattern: open, well-drained country rather than closed rainforest. Species occupy grassland and pampas, thorn scrub, the dry Chaco woodland, rocky hill slopes, and in Chile the semi-desert and matorral of the coastal ranges. G. pulchra is the outlier, living in the more humid grassland and forest edge of southern Brazil.

Within that habitat the spider needs one thing above all: a dry retreat. These are animals of thin soils, rock cracks and abandoned burrows, and prolonged saturation genuinely harms them. A drainage line or a stone outcrop will hold far more tarantulas than the flat ground around it.

Are Grammostola tarantulas venomous?

Yes — almost all spiders are — but not in any way that endangers a person. Grammostola venom is adapted to insects and small vertebrates, no antivenom exists for any theraphosid because none is needed, and no human death has ever been attributed to a tarantula bite. Clinical series of theraphosid bites report local pain, puncture marks, bleeding and swelling that resolve within hours to a couple of days.

The defence that actually causes injury is the hair. As New World theraphosines, Grammostola species carry urticating setae on the upper abdomen — microscopically barbed bristles that the spider kicks free with its hind legs, sending a cloud of them at an approaching face or nose. They lodge in skin, eyes and airways, causing itching, welts and, in the eye, serious inflammation. A spider that has been flicking shows a bald patch on the abdomen until its next molt. Old World genera such as Cyriopagopus have no urticating setae at all, and answer a threat with a far more painful bite.

Can Grammostola tarantulas bite?

They can, but among tarantulas this genus is about as reluctant as they come. Its temperament is why G. rosea, G. pulchra and G. pulchripes are the species most often recommended to beginners in the hobby. A disturbed Grammostola walks away, then raises its abdomen and flicks hairs; biting is the last item on the list. Grammostola iheringi is the genus's exception, noticeably faster and more defensive than its relatives.

A bite delivers sharp mechanical pain from fangs several millimetres long, two puncture marks, some bleeding, and local swelling that settles over a day or two. Wash the wound with soap and water, apply a cold pack, and keep it clean — the realistic complication is a secondary bacterial infection of the punctures, not the venom itself. Seek medical advice if pain escalates, redness spreads, or there are signs of an allergic reaction.

Ecological importance and behavior of Grammostola tarantulas

Grammostola is a solitary, nocturnal, sit-and-wait predator. The spider spends daylight underground and comes to the burrow mouth at dusk. The wild diet is invertebrates — crickets, beetles, grasshoppers, roaches, moths — with occasional small vertebrates such as lizards or young frogs for the biggest females. Mealworms, often listed as a food of this genus, are a captive feeder insect, not a natural prey item.

Natural predators: the most important are pompilid spider wasps, the tarantula hawks, which paralyse an adult and seal it alive with an egg. Coatis, skunks, armadillos, foxes, snakes, owls and other birds take exposed spiders, and parasitic flies and nematodes attack egg sacs and adults alike.

Prey-predator dynamics: in open grassland and scrub, burrowing tarantulas are a steady drain on ground-dwelling insects. A female holds one burrow for many years, so each occupied hole is a long-term feature of the local food web, and abandoned burrows shelter frogs and lizards.

Seasonal behaviour: mature males leave their burrows and walk for weeks searching for females in the warmer months, and it is these wandering males that people meet crossing roads and tracks. Females continue to molt for life and are among the longest-lived spiders on earth — commonly fifteen to twenty years, with credible records beyond that. Males live roughly four to six years in total.

Relationship with humans: harmless and useful. The docile reputation of the genus has also made it one of the most heavily traded of all tarantulas, and wild collection of slow-growing animals is a real concern for species with small ranges.

Species in the genus and similar tarantulas

Quick facts

Did you know?

• The genus was named by Eugène Simon, the French arachnologist who described more spider species than anyone before or since.
• A great many pet "rose hairs" are not Grammostola rosea at all but Grammostola porteri — one of the most persistent misidentifications in the whole hobby.
• Rose hairs are notorious for refusing food for months on end while remaining in perfect health. A fasting tarantula with a plump abdomen is usually preparing to molt, not starving.
• A female lines her egg sac with hairs plucked from her own abdomen, turning a defensive structure into an anti-predator wrapping for the eggs.
• Because the hairs are shed at each molt, the bald patch left by a spider that has been flicking is temporary — the new coat comes back with the new skin.

In summary, Grammostola is the gentle heavyweight of the tarantula world: a South American genus of slow-growing, long-lived burrowers whose venom is unremarkable, whose temperament is famously calm, and whose only real weapon against a human is a cloud of itching hairs.