Brazilian Redrump Tarantula (Grammostola actaeon)

Physical description and identification

The Brazilian redrump is a medium-large, heavily built terrestrial tarantula with a two-tone look that makes it easy to recognise within its genus: an almost uniformly black carapace and legs, and an abdomen densely covered in dark red to rust-coloured setae. In low light the red reads as a warm brown; in sunshine it is unmistakable. The whole animal has a woolly, long-haired texture, which is where its other common name, the Brazilian woolly black tarantula, comes from.

Adults

• Size: the usual figure of 12–15 cm is the leg span, not the body length. The body itself measures roughly 5–6 cm. That makes it a solid but mid-sized member of Grammostola, clearly smaller than the Entre Rios tarantula or the Chaco golden knee.
• Colour: black overall, with the red concentrated on the abdomen. Longer reddish or golden guard hairs are often scattered over the legs as well, catching the light at the edges.
• Urticating hairs: the red patch on the abdomen is not only pigment. It is the field of barbed urticating hairs the spider rakes off with a hind leg when threatened, and an individual that has kicked repeatedly develops a bald, dark patch there until the next moult.
• Sexing: mature males are leggier and much lighter, with swollen pedipalp bulbs and tibial hooks on the front legs. Females stay bulky and live several times longer. Until maturity, a shed skin is the only reliable way to sex a specimen.

Eggs and egg sac

This species is reported to lay an unusually small clutch for a tarantula — in the region of 40 to 50 eggs, where many theraphosids of the same size produce several hundred. The individual eggs are correspondingly large, and the female encloses them in a compact silk sac that she keeps inside her burrow and guards until the young emerge. Fewer, better-provisioned offspring is a recognisable strategy among cool-climate spiders, where a short active season limits how much a spiderling can grow before winter.

Spiderlings

Hatchlings are dark grey and plain, with no red on the abdomen at all. The rust colouring develops gradually over successive moults, and a juvenile is easily mistaken for a young Brazilian black tarantula. Growth is slow: females take several years to mature, moulting a few times a year while young and roughly annually as adults. Our guide to spider moulting explains the process and why a moulting tarantula must not be disturbed.

The web and hunting

No capture web is built. The silk goes into lining a burrow or the cavity under a log or stone, sealing the walls and forming a thin mat at the entrance that transmits the footsteps of passing insects. The spider sits just inside after dark with its front legs on that mat, and ambushes anything that crosses it. The egg sac is the other main use of silk.

Where the Brazilian redrump tarantula lives

Grammostola actaeon is a spider of the far south of Brazil — chiefly Rio Grande do Sul and Santa Catarina — with records extending into Uruguay. This is temperate country, not tropical: a mosaic of Atlantic forest remnants, araucaria woodland, grassy campos and rocky slopes, with warm summers and genuinely cold winters. Calling it an Amazonian or rainforest species, as popular accounts sometimes do, is wrong.

Within that landscape it is strictly terrestrial and fossorial. It shelters in a burrow dug into a bank or the base of a slope, or occupies a ready-made cavity beneath a rock, a fallen trunk or dense root growth, and it is sedentary enough that one female may hold the same refuge for many years. Activity is strongly seasonal, dropping off sharply through the southern winter.

Are Brazilian redrump tarantulas venomous?

Yes, and like every tarantula it uses that venom to subdue insects. For people it is not medically significant. Clinical reviews of theraphosid bites place New World terrestrial species such as this one at the mild end of the scale: local pain and swelling, no systemic effects, no antivenom required, and no deaths recorded from any Grammostola species.

The defence that matters here is the hair. As a New World tarantula, the Brazilian redrump carries urticating setae on the abdomen — microscopically barbed bristles it kicks into the air with a hind leg when it feels cornered. They are aimed at the face of an approaching mammal, and they work: the barbs lodge in skin and mucous membranes and are difficult to remove. Old World species such as the king baboon tarantula have no hairs of this kind and compensate with much more potent venom.

Can Brazilian redrump tarantulas bite?

They can, but it is well down their list of responses. A disturbed redrump retreats first, kicks hairs second, may raise its front legs in a threat posture third, and bites only if it is pinned or grabbed. Documented bites from the genus are rare.

When one does happen, the fangs cause more trouble than the venom. They are large and strike downward in parallel, so the injury is two deep punctures with sharp immediate pain, some bleeding, and redness and swelling that fade over a day or two. Cramping in the affected limb has been reported after theraphosid bites in general; it is unpleasant but not dangerous. The realistic complication is a secondary skin infection at the puncture site.

Wash the wound thoroughly with soap and water, apply a cold pack, keep the limb raised and take an ordinary painkiller if needed. Get medical advice if the site becomes hot, spreading and increasingly painful after a day or two, if you develop breathing difficulty, faintness or a widespread rash suggesting an allergic reaction, or if hairs may have entered an eye. Do not cut, suck or burn the wound, and do not apply home remedies.

Ecological importance and behaviour of the Brazilian redrump

This is a long-lived ambush predator that hunts at night from the mouth of its retreat. In the wild it takes ground-living arthropods: crickets, grasshoppers, beetles, cockroaches, moths, millipedes and other spiders, with a small frog or lizard taken opportunistically. The tidy lists of crickets, dubia roaches, locusts and mealworms that circulate for this species describe what captive animals are offered, not what it finds in southern Brazil.

Natural predators: ground-foraging birds, snakes, lizards and small carnivorous mammals take adults caught away from cover, and spiderlings are vulnerable to almost everything, including other spiders. The specialist enemy is the pompilid spider wasp, which stings a tarantula into paralysis, drags it into a chamber and lays a single egg on the living body.

Prey–predator dynamics: because a female may occupy one burrow for fifteen years or more, she applies steady predation pressure to the same square metres of ground for a long time. With only forty or fifty eggs per clutch, this species cannot offset losses through sheer numbers the way most tarantulas do, which makes adult survival and habitat continuity unusually important to it.

Seasonal behaviour: feeding and mating concentrate in the warm months. Mature males abandon their retreats and wander to find females, and die within roughly a year of that final moult; females carry on through many seasons.

Relationship with humans: the species is harmless and rarely encountered, since it stays underground and its range is largely rural. Its colouring has made it sought after in the international tarantula trade, where it is considered scarce; that scarcity, combined with small clutches, slow growth and the continuing clearance of southern Brazilian forest and grassland, is the reason wild collection is a genuine concern for this species rather than a theoretical one.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1903 by the British zoologist Reginald Innes Pocock, then in charge of arachnids at the Natural History Museum in London.
• The name actaeon comes from Actaeon of Greek myth, the hunter torn apart by his own hounds — one of many classical names Pocock gave to spiders.
• A clutch of forty to fifty eggs is extraordinary for a tarantula of this size; large species commonly produce several hundred and some exceed a thousand.
• A bald black patch on the abdomen is not disease. It marks where the spider has kicked away its urticating hairs, and the coat is restored at the next moult.
• Tarantulas are mygalomorphs, an ancient lineage whose fangs strike straight down rather than pinching sideways, which is why they must rear up before biting.

In summary, the Brazilian redrump is a temperate, burrow-dwelling tarantula of southern Brazil and Uruguay: black with a rust-red abdomen, mild-venomed, slow-growing and defended by hairs rather than fangs. Look for red confined to the abdomen on an otherwise black spider, and check the size before deciding it is not its much larger cousin from Entre Ríos.