Mexican Red Knee Tarantula

ORDER: Araneae

FAMILY: Theraphosidae

GENUS: Brachypelma

SPECIES: smithi

This is a dark spider overall with a black abdomen covered by brown hairs. Its legs have orange to dark red-orange "knees" and some smaller patches of orange on the legs. Carapace is usually a creamy beige with a distinctive black square. Can grow to 5 and 1/2 inches in size. A tarantula has two major body sections: the cephalothorax and the abdomen. Appendages on the cephalothorax include four pairs of legs, a pair of pedipalps and a pair of fang tipped chelicerae. (Chelicerae are appendages each of which is made up of a fang and a basal segment containing venom glands and teeth used to macerate prey.) Of the legs, the first two are for holding prey, and the others are used for walking. Mature males have special copulatory organs on the pedipalps and hooks on the first pair of legs. The abdomen has two pair of spinnerets posteriorly.

Common in some coastal areas of Mexico. They are found in dry areas with sparse vegetation. Burrows are found at the bases of cacti or similar plants or at the base of rocky areas, etc.

Large insects and small mammals. Spiders are unable to digest food internally so digestive juices are injected into prey and the remains sucked out.

Nocturnal and solitary. Before copulation the male takes up into his palps sperm that he has deposited on a specially spun sperm web. The sperm is then implanted in the female's storage organs and may remain there for some time. Females lay several hundred eggs which she covers with a sticky liquid containing the sperm. The eggs are wrapped in silk and carried between the mother's fangs. Eggs hatch between one and a half and two and a half months. Spiderlings are guarded for several weeks. Males reach sexual maturity at an age of 4-5 years. Females mature two to three years later than males, a factor which would prevent inbreeding in the wild. In captivity, with optimal conditions, these spiders may mature at a younger age than their wild counterparts. Females may live for 25 years or more. Males rarely live past 10 years.

Two claws on each foot enable the spider to grip and climb up slippery surfaces. Pedipalps (appendages occurring in front of the walking legs) help to guide the animal while moving and eating. It has eight eyes positioned around the head to see both forward and backwards. They do not have great vision, so use their sensitive leg hairs for guidance. Spiders do not hear as such, but they have a very well-developed ability to sense vibrations, both airborne and those transmitted through the surface on which they are standing. This sensory ability is sited in a number of different receptors on their body, but especially on the appendages.

Spiders are known as arachnids; scorpions also belong to this group. Although usually peaceful, when threatened a Mexican Red Knee will rear up to display its fangs and the bristles on its abdomen. By rubbing its backlegs, hair can be flipped as a defense. These "urticating" hairs are barbed and in contact with soft tissue they dig in and cause an irritation. The two hollow fangs may be used to inject venom. People should handle this tarantula very carefully since some may be allergic or super sensitive to the venom or the hairs they flick. Tarantulas molt usually once a year. Molting of the old exoskeleton allows the spider to grow larger, gives it a completely new set of undamaged sensory and protective hairs and also gets rid of any parasite or fungus that might have started to grow on its exterior. Lost or damaged appendages are regenerated gradually with each succeeding molt, even during the adult phase.


Habitat destruction and the pet trade are of concern for these spiders. Listed on Appendix II CITES (threatened and requiring special permits for transfer between countries).


  1. Gurley, Russ. A Color Guide to Tarantulas of the World. 1993. Published by Russ Gurley and Living Art, Ada, OK.
  2. Internet: (Auckland Zoo Education Service)
  3. Preston-Mafham, Rod. The Book of Spiders. 1998. Chartwell Books, Edison,NJ.
  4. Vosjoli, Philippe de. Arachnomania: The General Care and Maintenance of Tarantulas and Scorpions. 1991. Advanced Vivarium Systems, Lakeside, CA.
  5. Wolff, Robert. "Terrific Tarantulas", Carolina Tips. March, 1994.