Mexican Golden Red Rump Tarantula (Brachypelma albiceps)

Physical description and identification

Few Mexican tarantulas are as easy to name on sight. The carapace is pale — creamy white, sandy grey, straw-yellow or faintly rose — above an abdomen so dark that the coppery red hairs covering it seem to glow. A light shield in front and a red-dusted black body behind is the whole identification in one glance.

Adults

• Size: a mature adult has a diagonal leg span of about 12–14 cm (roughly 5 inches). The body itself measures only about 5–6 cm from the front of the carapace to the spinnerets. Older accounts that give “12.5 cm body length” are quoting leg span, not body length.
• Colour: the carapace ranges from sandy grey through pale gold to a soft rose tint, always noticeably lighter than the rest of the animal. The abdomen is black and thickly clothed in reddish-orange setae. Legs are dark brown to black with a bronze sheen along the bristles.
• Other features: the first two pairs of legs frequently look lighter than the hind two pairs. Like all tarantulas this species has two pairs of book lungs, downward-striking fangs and eight small eyes crowded on a raised mound at the front of the carapace. Mature males are leggier and slimmer, with hooked tibial spurs and swollen pedipalps.

Eggs and egg sac

A female is mated in the warm months and can delay laying for weeks while the sperm is stored. She then spins a thick silk cocoon inside the burrow and fills it with a large clutch — several hundred eggs, with counts of roughly 500 to 900 reported for well-fed females. She turns and guards the sac constantly, and incubation takes about eight to ten weeks.

Spiderlings

Newly emerged spiderlings are small, drab and brown, with none of the adult contrast. The golden carapace and red abdominal hairs appear gradually, one moult at a time, and a youngster may need three or four years to look like a species photograph. Slings stay near the mother's burrow briefly, then scatter to dig their own shallow shelters.

The web and hunting

The Mexican golden red rump does not build a capture web. It is an ambush predator that waits at the mouth of a burrow or under a rock and seizes whatever walks within reach. That does not make it silk-free: it lines the burrow wall, seals the entrance with a silk plug during moults and lays a thin mat of threads across the doorstep that carries the footsteps of passing insects straight to its legs. Unlike the engineered snares in our guide to spider webs, a tarantula uses silk as a floor and an alarm system, not as a trap.

Where the Mexican golden red rump tarantula lives

Brachypelma albiceps is endemic to southern Mexico. It was described from Amula in the state of Guerrero — the origin of its second common name, the Amula red rump — and the known range covers the highlands of Guerrero and the southern part of neighbouring Morelos. Everything about it is a highland animal: the populations sit well above the coastal plain, in country that is warm by day, cool at night and strongly seasonal, with summer rains and a long dry winter.

There it occupies dry scrub, thorn forest and open pine-oak slopes, digging or adopting burrows at the base of rocks, under fallen agave leaves and in the packed soil of banks and road cuttings. A burrow is a modest affair by tarantula standards, often little more than a silk-lined chamber under a stone. The spider spends daylight underground and comes to the entrance after dark, so it is found far more often by turning rocks than by walking with a torch. Its range does not overlap with the Pacific-slope members of the genus, the Mexican red knee and the Mexican fireleg.

Are Mexican golden red rump tarantulas venomous?

Yes, in the sense that every tarantula is venomous: it kills insects with venom delivered through a pair of large, downward-striking fangs. The venom of Brachypelma albiceps is not medically significant to people. No deaths, tissue necrosis or systemic syndrome are attached to this species or to any other New World theraphosid, and clinical reviews of tarantula bites describe local pain, redness and swelling that settle within hours to a couple of days.

The part of the animal that deserves respect is not the fangs but the abdomen. Like other New World tarantulas it carries urticating setae — barbed hairs kicked off the abdomen with the hind legs when it is alarmed. They lodge in skin and cause an itchy, stinging rash lasting days. In the eyes they can embed in the cornea and cause a stubborn inflammation that needs an ophthalmologist, so never lean over a disturbed tarantula and always wash your hands afterwards.

Can a Mexican golden red rump tarantula bite?

It can, but it very rarely does. The species is calm and slow by tarantula standards and its defensive sequence is built to avoid a fight: first it walks away, then it raises the front of the body and flicks hairs, and only if pinned or squeezed does it strike. A bite from an animal this size is mostly a mechanical injury — the fangs are several millimetres long and puncture skin like two thick needles.

Treat a bite simply. Wash with soap and water, apply a cold pack and take an ordinary painkiller if you need one, then watch the puncture for infection over the next few days. Seek medical care if pain escalates instead of fading, if the area becomes hot and spreading, or if you develop breathing difficulty, a widespread rash or faintness — signs of an unusual allergic reaction rather than of the venom. Do not cut, suck or apply chemicals to the wound.

Ecological importance and behaviour of the Mexican golden red rump

This tarantula is a keystone invertebrate predator of dry Mexican highland soil. It sits at the burrow mouth after dark and takes beetles, cockroaches, crickets, grasshoppers, moths and the occasional small lizard, carrying prey back underground to feed. A single adult can hold a territory for a decade or more.

Natural predators: adults are hunted by coatis, skunks, snakes and large birds, and the burrow offers no protection against tarantula hawk wasps of the genera Pepsis and Hemipepsis, which paralyse a spider and lay a single egg on it. Spiderlings are eaten by almost everything — see what eats spiders.

Prey-predator dynamics: removing large ground insects relieves grazing pressure on highland vegetation, and abandoned burrows shelter frogs, geckos and beetles.

Seasonal behaviour: activity peaks in the summer rains. Mature males abandon their burrows and wander in search of females, which is when nearly all wild sightings happen; a mature male usually dies within a year, while a female may still be breeding at fifteen. Both sexes fast and seal themselves in before moulting, and a freshly moulted spider is soft and defenceless for days.

Relationship with humans: the animal is harmless and useful in the field. Its main contact with us is the exotic pet trade, where its docility and colour made it popular. Like the whole genus Brachypelma it is on CITES Appendix II, so international movement needs permits; wild collection and habitat clearance in the Guerrero highlands are the real conservation problems.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The British zoologist Reginald Innes Pocock described the species in 1903 from Amula, Guerrero. Albiceps is Latin for “white head”, after the pale carapace.
• It spent years in the genus Brachypelmides, which is why older keeper literature still calls it Brachypelmides albiceps.
• In 2020 Mendoza and Francke split the dark-bodied “red rump” species out of Brachypelma into the new genus Tliltocatl, from the Nahuatl for black and spider. B. albiceps stayed in Brachypelma.
• Urticating hairs are a New World invention. Old World tarantulas such as the king baboon have none and rely on speed, threat displays and a far more painful bite.
• Every Brachypelma species has been on CITES Appendix II since 1994 — among the first spiders anywhere to be given international trade protection.

In summary, the Mexican golden red rump tarantula is a slow, long-lived highland burrower whose pale carapace and red-dusted black abdomen make it unmistakable in its small corner of Guerrero and Morelos. It is not dangerous, its worst weapon is a cloud of itchy hairs, and the real threat runs the other way — toward a spider whose habitat is shrinking.