Tarantula, red-kneed

Euathlus smithi (also Brachypelma smithi)

phylum: Arthropoda

class: Arachnida

order: Araneae

family: Theraphosidae

status: Lower risk; near threatened, IUCN

range: Mexico

Description and biology

The red-kneed tarantula is one of the biggest spiders in the world, with a body length from 2.5 to 4 inches (6.4 to 10.2 centimeters) and a leg span of 4 to 7 inches (10.2 to 18 centimeters). It can weigh up to 2.5 ounces (71 grams). The tarantula's body is dark brown and covered in tiny hairs. The joints (knees) on its eight legs are bright orange and red, which is the basis for its name. It has two claws on the end of each of its legs for climbing and gripping. Although the red-kneed tarantula has eight eyes set above its mouth to give it forward and backward vision, it has very poor eyesight. It uses its sensitive leg hairs to feel its way about.

The red-kneed tarantula lives in a burrow it has dug out underground and lined with its spun silk. Its diet consists of centipedes and millipedes, beetles, crickets, grasshoppers, small frogs, lizards, and sometimes mice. It hunts at night, locating its prey by means of a special sensitivity to its sounds and vibrations. The tarantula sits quietly, hidden in the dark, and then springs upon its victim. It grasps the prey with its two pedipalps (special appendages located near the mouth), and enfolds it with its eight legs and then bites it, injecting its venom. Tarantulas cannot digest food inside their own bodies; the venom they inject must serve two purposes. First, it stuns the prey into submission, and then it begins to digest the animal, turning its insides to liquid proteins and fats. The tarantula then sucks out the predigested liquid.

In late summer, male tarantulas look for females to mate. The male enters a female's burrow and then uses his pedipalps to inject sperm into the female's reproductive tract. He has to be very careful, though, because the female may attempt to kill and eat him. After mating, the female spins a web and lays anywhere from 50 to 700 eggs upon it. She then wraps the eggs in the silk ball and carries them between her fangs to incubate (keep warm until ready to hatch) for several weeks. Male tarantulas usually live about 8 years, while a female may live between 20 and 30 years.

Despite people's fears, red-kneed tarantulas are not as dangerous as they look. Although their bites are painful, they are generally not any more powerful than a bee sting. When threatened, red-kneed tarantulas display their red bristles and sometimes rub their back legs in order to drop hairs on their enemy. The hairs can cause rashes and even blindness. Even humans handling these spiders get rashes from their hairs. Generally, though, the red-kneed tarantula is not aggressive to humans. For this reason and because of its beautiful coloration, this tarantula became prized as a pet and has been one of the favored spiders for use in movies.

Habitat and current distribution

Red-kneed tarantulas can be found in deserts and rain forests. They are known to occur in southwestern Mexico along the Sierra Madre mountain range along the Pacific coast in the Mexican states extending from Jalisco (pronounced hah-LEES-coe) and Colima down to Oaxaca (pronounced wah-HAH-cah).

History and conservation measures

The friendliness to humans, brilliant coloring, and long life of the red-kneed tarantula have made the species verypopular among spider collectors. Up until 1985, thousands of these tarantulas were imported from Mexico and then sold as pets. After years of this trade, the population of spiders in the wild declined, and in 1985 the Convention on International Trade in Endangered Species (CITES) banned the exportation and importation of red-kneed tarantulas that have been caught in the wild. Only red-kneed tarantulas bred in captivity can be traded legally. This is the only species of tarantula to be protected under CITES. Destruction of its habitat in Mexico is also responsible for decline in this species' population.