Mexican redknee tarantula  (Brachypelma smithi)

This venomous but docile tarantula is the most common spider used in movies due to its large size and beautiful colouration. A particularly striking tarantula, the Mexican redknee has a dark brown body and legs, with orange-red leg joints (3). The ends of the legs can detect vibrations, smells and tastes, to help the tarantula locate prey and the opposite sex, although it also has a group of eight eyes on the top of the carapace (4).

Mexican redknee tarantulas are found along the central Pacific coast of Mexico, from southern coastal Jalisco to north-western Oaxaca State and inland to the states of Mexico and Morelos (5).

Lives in ground burrows (6), in rocky areas under thorny vegetation, usually in scrubland or desert, dry thorn forest or tropical deciduous forest (4) (5).

In the wild, Mexican redknee tarantulas mate in the summer, shortly after the male's maturing moult, usually in the rainy season (July and August) (7). Mating occurs in or near to the female's burrow, where the male uses his pedipalps (front limbs) to transfer his sperm into openings in the underside of the female's abdomen. After mating, some females will try to kill and eat the male, although this has never been observed in the wild (7). The sperm and eggs are stored in the female's body and not laid until spring. In the spring, the female deposits hundreds of eggs and the sperm onto a silk mat which she has made and then fashions this mat into a ball or egg sac. Fertilisation takes place within minutes and the spiderlings hatch in just less than three months (7), but the spiderlings remain in the egg-sac for a further three weeks. Once out of the egg-sac they spend two weeks in the burrow before dispersing. Males mature at about four years of age and females two to three years later at about six or seven years old (3). They are a long-lived species with females living up to 25 to 30 years old (4); however males only live about one year after maturity (7).

Hunting at night by lying in ambush, the Mexican redknee tarantula attacks insects, small frogs, small lizards, and mice. An area on the end of each leg is sensitive to smells, tastes and vibrations, and this is used to detect prey. The tarantula holds its prey with its pedipalps (front limbs) and injects it with venom delivered via two hollow fangs. This venom has a double purpose, paralysing the prey as well as beginning digestion. Once the venom has acted, the tarantula is able to suck up the proteins and fats of its prey, leaving just a small ball of undigested body parts (4).

This usually docile tarantula will kick hairs off the abdomen with its hind legs when threatened, which cause blindness if they hit the eyes of a predator and can also cause a rash on the skin (4).

This particular species is the most popular captive tarantula species in the world, and prior to 1985 it was collected in thousands (6). Habitat loss is now the major threat to the Mexican redknee tarantula.

Listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) in 1985, the Mexican redknee tarantula can now only be traded internationally according to quotas and with trade permits (6), and in Mexico permits are required to collect or remove any spider from the Theraphosid family (5).

For further information on the Mexican redknee tarantula see:

• Locht, A., Yáñez, M. and Vázquez, I. (1999) Distribution and natural history of Mexican species of Brachypelma and Brachypelmides (Theraphosidae, Theraphosinae) with morphological evidence to support their synonymy. The Journal of Arachnology, 27(1): 196-200.
• West, R.C. (2005) The Brachypelma of Mexico. Journal of the British Tarantula Society, 20(4): 108-119.

Authenticated (25/03/08) by Rick West.
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