Mexican Red Knee Tarantula

Mexican red knee tarantula（圖片來源：George Chernilevsky，CC0 1.0 公共領域）

The Mexican red knee tarantula (Brachypelma smithi) is native to the Pacific coastal region of Mexico, particularly in the dry scrublands and tropical deciduous forests of Guerrero. In the wild, these spiders usually inhabit burrows among rocks and tree roots, or they expand pre-existing cavities in the soil. These burrows typically have a narrow entrance that leads to one or two concealed chambers, protecting the spider from predators such as white-nosed coatis, lizards, and birds. Female spiders spend most of their lives inside these burrows, hunting by ambush and waiting for insects, frogs, or even small mammals to approach.

This species is robust in build, with adult individuals reaching a leg span of about 12 to 14 centimeters. Females are generally larger than males and may live for 25 to 30 years, while males usually survive only 5 to 10 years. Their appearance is highly distinctive: the body is black, while the leg joints display bright red or orange-red coloration, giving rise to the name “red knee.” Sexual differences extend beyond lifespan. After reaching maturity, males develop specialized reproductive organs on their pedipalps and stop molting. Females, however, continue to molt periodically even after adulthood, which helps remove external parasites or damaged body hairs.

In nature, breeding typically occurs during the rainy season. After reaching maturity, a male constructs a sperm web and deposits sperm from his testes onto the web. He then uses his pedipalps to collect the sperm before approaching a female's burrow to attempt mating. Although females may sometimes attack the male, he often manages to retreat safely. After mating, the female produces an egg sac in spring containing approximately 200 to 400 eggs. She carefully guards the sac and regularly rotates it to maintain proper humidity and temperature. Once the spiderlings hatch, they remain inside the mother's burrow for several weeks before dispersing and beginning independent lives.

Mexican red knee tarantulas are widely known for their calm temperament. Even when threatened, they are more likely to raise their front legs or flick urticating hairs from the abdomen as a defensive display rather than bite. Their venom is not considered dangerous to humans, though it may cause pain and irritation. Because of their striking appearance, slow movements, and relatively manageable care requirements, they have become one of the most popular tarantulas kept as pets.

Mexican red knee tarantula（圖片來源：André ALLIOT，CC0 1.0 公共領域）

Housing Requirements in Captivity

When keeping this species in captivity, providing an enclosure that resembles its natural environment is extremely important. A suitable terrarium can be a transparent glass or plastic container. The length and width should ideally be two to three times the spider's leg span, while the height should be roughly equal to the leg span to reduce the risk of injury from falls. Although Mexican red knee tarantulas are capable of climbing, they are not particularly stable climbers, and an enclosure that is too tall may increase the chance of accidental falls.

Temperature should be maintained between 24 and 27°C, with relative humidity around 60% to 70%. If the environment becomes too dry, occasional misting or evaporation from a water dish can help regulate humidity. The enclosure should provide adequate ventilation but must be protected from direct sunlight or strong lighting. As nocturnal animals, these spiders do not require ultraviolet lighting.

The substrate may consist of a mixture of peat moss, coconut fiber, and vermiculite, with a depth of at least 7 to 10 centimeters to allow the spider to dig and modify its burrow. Pieces of bark, wooden shelters, or ceramic pots should be placed inside the enclosure to serve as hiding places that resemble natural burrows, which helps reduce stress in the spider. Artificial plants may also be added to create a natural appearance without the hygiene problems associated with decaying live plants.

The enclosure must be kept secure at all times to prevent escapes. Mexican red knee tarantulas should not be housed together, as they are solitary animals and may engage in cannibalism if kept communally.

Feeding Conditions

Mexican red knee tarantulas are carnivorous and primarily feed on large insects. In captivity, the most common live feeder insects include crickets, Dubia roaches (Blaptica dubia), and mealworms. Occasionally offering different insects can increase dietary variety. Spiderlings may initially be fed fruit flies or small crickets, and the prey size can be increased gradually as the spider grows.

Live prey is necessary because these tarantulas detect food through vibrations. After capturing prey, the spider injects venom and digestive enzymes through its fangs, liquefying the internal tissues before consuming the resulting fluid. The remaining insect exoskeleton is typically wrapped into a small pellet and discarded. For this reason, keepers should regularly inspect the enclosure and remove leftover remains to prevent mold or parasite growth.

Adult spiders usually need feeding once or twice per week. Overfeeding should be avoided, as excessive food may lead to obesity or physiological stress. If the spider is preparing to molt, it will often refuse food. During this time, all live prey should be removed from the enclosure immediately, since insects such as crickets may bite the spider while its exoskeleton is still soft, potentially causing fatal injuries.

A shallow, wide water dish should always be provided. The water should be dechlorinated and replaced daily to maintain cleanliness. Spiderlings may drink from droplets present on enclosure surfaces. Sponges or gel-based water sources should be avoided because they can easily harbor bacteria.

Breeding Conditions

Successful breeding of Mexican red knee tarantulas requires simulating rainy season conditions. Humidity should be increased to around 80%, and temperatures may be slightly reduced. Mature males construct a sperm web on the ground and transfer sperm to their pedipalps before approaching a female.

The mating process must be conducted carefully because the female may attack the male due to defensive instincts. Breeders often introduce the male several days after the female has been fed and only when the environment is quiet and undisturbed.

If mating is successful, the female will produce an egg sac several months later that may contain several hundred eggs. At this stage, temperature and humidity must remain stable, and disturbances should be minimized. After the egg sac hatches, the spiderlings remain under the protection of the female for several weeks before dispersing. Once the young leave the mother, they should be separated promptly to prevent cannibalism.

The breeding process—from selecting healthy breeding individuals to simulating appropriate seasonal conditions and separating spiderlings—can be complex. Without sufficient experience, breeding attempts often involve considerable risk and may result in the loss of adult spiders or offspring. For most keepers, maintaining a single individual for observation is a more practical choice.

Preventing Invasive Spread

Because of its vivid coloration and calm temperament, the Mexican red knee tarantula has been widely exported around the world, and illegal trade has also occurred. In fact, this species was listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) as early as the 1980s, placing strict controls on international trade. Many wild populations have suffered from overcollection, so it is essential to obtain individuals through legal and responsible sources.

In regions outside its native range, escaped, released, or abandoned individuals could potentially establish populations if natural predators are absent. Such introductions may disrupt local ecosystems by affecting native insects and small vertebrates.

For this reason, pet owners must follow the principle of responsible ownership: never abandon or release captive animals into the wild. If circumstances prevent continued care, the spider should be transferred to a qualified keeper or an appropriate animal rescue organization. Releasing it into natural environments is unacceptable and contradicts the responsibilities of pet ownership.

Author: Shui-Ye You