Mexican Redleg Tarantula (Brachypelma emilia)

Physical description and identification

The Mexican redleg is a heavy, ground-dwelling tarantula of the family Theraphosidae, and like every tarantula it sits in the infraorder Mygalomorphae, whose fangs strike straight down in parallel rather than pinching together sideways. It is the type species of Brachypelma — the specimen against which the whole genus is anchored — and it is the easiest member of that genus to name on sight.

Adults

• Size: a mature female has a leg span of about 12–15 cm (5–6 in), with unusually large individuals reaching a little more. Figures of 18–19 cm quoted in some accounts describe the extreme rather than the norm. A heavy female weighs around 15–16 grams.
• Colour: the carapace is pale tan to cream, marked by a bold, clean black triangle — the single most useful field character in the genus. The femora are black, and from the second joint outward the legs are orange, salmon or rust red. The abdomen is black under a thick coat of reddish hairs.
• Eyes: eight small eyes clustered on one raised tubercle. Sight barely matters; vibration and the touch hairs on the legs do the work.
• Distinctive features: a dense patch of barbed urticating setae on the abdomen, the first line of defence. Females are larger and bulkier than males, which is the sexual dimorphism most often noted for this species; mature males have swollen palpal bulbs and hooked spurs on the front tibiae.

Eggs and the egg sac

The female wraps her eggs in a thick white silk sac deep inside the burrow — several hundred in one clutch — and guards it there, turning it regularly through the weeks before the young emerge. None of this is visible from outside; a burrow with a sac in it simply goes quiet.

Spiderlings

Newly emerged spiderlings are dark-bodied with pale, almost white legs, and look nothing like the adults. Colour arrives gradually over successive moults through the first years, the triangle appearing on the carapace only as the spider approaches maturity. Growth is slow: females need roughly six to seven years to mature and males four to five.

The web and hunting

The redleg spins no snare and catches nothing in silk, but it is far from silk-free. It lines the burrow, lays an apron of trip-threads across the entrance that carries the footfall of passing insects straight back to it, spins a mat to moult on and wraps the eggs. Hunting is ambush: the spider waits just inside the doorway after dark and lunges. For the contrast with true snare-builders, see our guide to spider webs.

Where the Mexican redleg tarantula lives

Brachypelma emilia is a Mexican endemic of the Pacific slope, recorded from Sinaloa and Nayarit south through Jalisco and Colima, along the seaward foothills of the Sierra Madre Occidental. That places it at the northern end of the genus, farther from the tropics than the red-kneed species of Guerrero and Oaxaca.

Older accounts describe the habitat simply as "mountainous forest", which is too vague to be useful. It is dry country: tropical deciduous forest and thorn scrub on rocky slopes, foothills and ravine sides, mostly below about 1,000 metres, that stand bare for half the year. What the spider needs is firm, well-drained soil with a stable cavity — a hollow under a rock, a gap beneath a fallen log, a root buttress or an abandoned rodent tunnel — which it enlarges and lines with silk rather than digging from scratch. Beyond the northern edge of its range the same ecological role passes to the duller, less banded species of Aphonopelma.

Are Mexican redleg tarantulas venomous?

Yes, but not dangerously. The venom is built for insect prey, and no death has ever been attributed to any Brachypelma species. No antivenom exists because none is needed, and a bite produces local pain, bleeding from the punctures and swelling that settle within a day or two.

The defence that causes real trouble is the hair. The abdomen carries barbed, detachable urticating setae which a disturbed spider rakes off with its hind legs, throwing a fine cloud into the air. On skin they cause itching, burning and a raised rash that can persist for a week or more; inhaled, they irritate the airways. The serious outcome is ocular: setae that reach the eye can embed in the cornea and cause ophthalmia nodosa, a stubborn granulomatous inflammation that has sometimes required surgical removal. Wash your hands after any contact with a New World tarantula or its enclosure, and keep them away from your face.

Can Mexican redleg tarantulas bite?

They can, but very rarely do. This is one of the calmest large tarantulas known, and its response to a threat is to walk away, or to turn its back and kick hairs, long before it considers the fangs. A bite means the spider has been cornered after every other signal was ignored.

The injury is largely mechanical. The fangs of a big female leave two deep punctures that bleed and ache like thorn stabs, and the local pain, warmth and swelling fade within 24 to 48 hours. Systemic symptoms are not expected from this genus; if they occur they indicate an allergic reaction rather than the venom. Wash with soap and water, apply a cold pack, and watch for spreading redness or discharge, which mean infection rather than envenomation. Seek medical care if the pain is severe, if a fang tip has broken off in the wound, or if there is breathing difficulty, facial swelling or dizziness. Never cut, suck or apply a tourniquet to a tarantula bite.

Ecological importance and behavior of the Mexican redleg tarantula

The redleg is solitary, territorial and strictly nocturnal, and an adult female may hold one burrow for decades. Through the dry season she seals the entrance with silk and soil and lives on stored reserves, emerging again with the rains.

Diet: mostly large ground-living arthropods — crickets, grasshoppers, beetles, cockroaches and moths — with other spiders and the occasional small frog or lizard taken opportunistically. Lists that include mammals, small birds and reptiles as staples overstate the case badly; vertebrate prey is an exception. Mealworms and similar items belong to captive feeding, not to a wild diet.

Natural predators: the specialist enemy is the tarantula hawk wasp, which paralyses the spider and lays a single egg on the living body. Coatis and skunks dig burrows open, and snakes, large lizards and ground-foraging birds take wandering spiders.

Prey–predator dynamics: a burrow-bound ambusher removes a steady flow of large insects from one patch of hillside for twenty or thirty years, while feeding the wasps, coatis and birds able to breach its defences. Because it is so long-lived and so slow to mature, its abundance is a fair indicator of how undisturbed a stretch of dry forest really is.

Seasonal behaviour: mature males abandon their burrows in the rains and walk in search of females, often crossing roads and rarely surviving the season. Females run on a different clock entirely, with 25 to 30 years documented, moulting and breeding throughout.

Relationship with humans: the redleg's docility made it a favourite of the tarantula hobby, and wild collection combined with dry-forest clearance thinned populations. All Brachypelma have been listed on CITES Appendix II since 1994, the species is protected under Mexican wildlife law, and legitimate specimens today are captive-bred.

Similar tarantulas and how to tell them apart

Quick facts

Did you know?

• The Scottish zoologist Adam White described the species in 1856 as Mygale emilia. Eugène Simon transferred it to his new genus Brachypelma in 1891 and made it the type species, which is why the redleg anchors the name.
• The carapace triangle is not decoration but the quickest diagnostic in the genus: no other Brachypelma carries a clean dark wedge on a pale head region.
• The genus around it has been redrawn twice recently — a 2017 revision separated B. smithi from B. hamorii, and a 2020 revision moved the red-rump species into the new genus Tliltocatl.

In summary, the Mexican redleg is a slow, mild, extraordinarily long-lived burrower of Mexico's north-western Pacific slope. Its venom is trivial to people and its temperament famously calm; the hazard worth respecting is the cloud of itching hairs, and the pressure worth worrying about is the one we apply to it.