King Baboon Tarantula (Pelinobius muticus)

Physical description and identification

The king baboon is one of the bulkiest tarantulas in Africa: a thick-set, rust-coloured spider with a low velvety sheen, a broad carapace and unusually heavy rear legs built for excavating hard ground. The colour runs from orange-rust through reddish brown, and the chelicerae carrying the fangs are noticeably darker. There is no banding or pattern to look for — bulk, colour and posture do the identifying.

Adults

• Size: the widely quoted 5.5 to 7.8 inches is the leg span, not the body. A large female spans up to about 20 cm, with a body length of roughly 7–9 cm. Males are smaller and lighter.
• Colour: rusty brown to orange throughout, with black fangs. The coat has a velvety, slightly glossy texture that catches the light.
• No urticating hairs: this is the single most important identification point. As an Old World species, Pelinobius muticus has no barbed abdominal bristles to flick — a bald patch on the abdomen means injury here, not defence.
• Stridulating organ: rows of stiff bristles between the chelicerae and the pedipalps and front legs, rubbed together to make an audible hiss. Very few tarantulas of this size are this loud.

Eggs and egg sac

The female builds a silk sac deep inside her burrow and lays a comparatively small clutch — roughly 30 to 180 eggs — which she guards underground for several weeks. Because the sac never leaves the burrow, it is almost never seen in the field.

Spiderlings

Hatchlings measure about 1 cm and begin digging almost immediately; a spiderling with no burrow is a spiderling in trouble. Growth is very slow: several years pass before a female reaches adult size, and mature females then molt roughly once a year. Our guide to spider molting explains what happens inside a shed skin.

The burrow and hunting

This species is an obligate burrower and among the most committed diggers in the family. It excavates a deep, often branching tunnel — well over half a metre in soft ground — and lines the walls and entrance with silk. That silk mat and the threads radiating from it work as a tripline: the spider sits just inside the mouth after dark, feels a beetle or cricket cross the silk, and strikes upward with astonishing speed before retreating underground. It builds no aerial snare at any point in its life; the silk is architecture and alarm system, never a net.

Where the king baboon tarantula lives

Pelinobius muticus is an East African species, recorded chiefly from Kenya and Tanzania. It lives in dry savanna, scrub and open grassland with firm soil it can tunnel into — hot by day, cool at night, with a long dry season.

It is strictly terrestrial and spends almost its entire life underground, emerging only at the burrow mouth to feed and, for males, to wander in search of females. A footnote on the source material: Pelinobius is a monotypic genus — one species and no others — not a family. It sits inside the tarantula family Theraphosidae, in the African subfamily Eumenophorinae, alongside the heavyweight Hysterocrates genus. The genus page for Pelinobius covers the classification in more detail.

Are king baboon tarantulas venomous?

Yes, and unlike most tarantulas people meet, its venom is worth taking seriously. Pelinobius muticus is an Old World theraphosid, and that lineage traded the urticating-hair defence for chemically stronger venom. There is no antivenom, no confirmed human death from any tarantula bite, and no tissue necrosis of the kind caused by recluse spiders — but an envenomation from this species is a painful medical event, not a scratch.

Reported effects include immediate intense local pain out of proportion to the wound, marked swelling, redness and itching lasting around five days, and — the hallmark of Old World theraphosid bites — delayed, prolonged muscle cramping and spasms that may begin hours after the bite and persist for days. Comparable, better-documented cases from the ornamental tarantulas of Asia have required hospital analgesia and muscle relaxants.

Can king baboon tarantulas bite?

Yes, and this is a species that will. It is defensive and quick to escalate: disturbed at its burrow it rears back on its hind legs, lifts the front pair, exposes the fangs and hisses loudly, and it follows through if the threat continues. Almost all bites are provoked, but the provocation needed is small.

What to do if you are bitten: move away from the spider and stay calm. Wash the puncture wounds with soap and water and apply a cold pack; keep the bitten limb still and elevated. Take a photograph of the spider if you safely can, because identification changes what a clinician expects. Seek medical care — do not wait it out at home. Tell the clinician that this is an Old World tarantula and that delayed muscle cramps are characteristic, since treatment is symptomatic: strong analgesia, muscle relaxants and observation. Get urgent care if cramps spread beyond the bitten limb, if you have chest tightness, breathing difficulty, a widespread rash or faintness, or if the wound becomes hot and increasingly painful after a day, which suggests infection.

Do not cut, suck, burn or apply a tourniquet to the wound, and do not use home remedies. This species is kept by experienced keepers precisely because it is not a spider that tolerates handling — that is context, not encouragement.

Ecological importance and behaviour of the king baboon tarantula

In East African savanna this is a long-lived ambush predator and a substantial one. It takes large insects — beetles, crickets, grasshoppers, cockroaches — along with the occasional small lizard or other small vertebrate that crosses its tripline. It hunts only at night and only within a body length or two of its burrow, so its impact is concentrated but constant, and it sits among the larger invertebrate predators in that habitat.

Natural predators: baboons dig tarantulas out of burrows and are the source of the common name for African theraphosids; mongooses, monitor lizards, snakes and large birds also take them. Parasitoid spider wasps are the specialist threat, paralysing a spider and laying an egg on it inside its own burrow.

Prey–predator dynamics: the deep burrow is the whole strategy. It buffers the spider against heat, drought and most predators, and it lets an animal with a very low metabolic rate survive long gaps between meals. Small clutch sizes are the trade-off: this species invests in a few well-provisioned young rather than the thousand-egg sacs of the giant South American species.

Relationship with humans: encounters are uncommon because the spider rarely leaves its burrow. It is heavily sought after by collectors, and wild-caught animals have historically dominated supply, which matters for a slow-maturing species. Kenya and Tanzania both regulate the export of wildlife, and captive-bred stock has become the responsible source.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1885 by the German arachnologist Ferdinand Karsch, and it remains the only member of its genus — Pelinobius has never gained a second species.
• It is routinely ranked as the second largest spider in Africa, behind the rarely seen Hercules baboon spider.
• The hiss is real stridulation, not air being forced out: stiff bristles between the chelicerae and the front limbs are scraped together, loud enough to hear from a metre away.
• "Baboon spider" is an African name for theraphosids generally, said to come from the resemblance of the leg tips to a baboon's fingers — and from baboons digging the spiders out to eat them.
• Its hind legs are visibly thicker than the front pairs, an adaptation to shifting hard, dry soil that few other tarantulas share.

In summary, the king baboon tarantula is an Old World heavyweight that lives almost entirely underground. It has no urticating hairs, warns with a hiss and a raised threat posture, and backs that up with a bite that causes real, days-long pain. Treat it as a spider to observe and leave alone, not one to pick up.