Mexican Redknee Tarantula, Brachypelma smithi

Redknee Tarantula, Brachypelma smithi. Photographs taken in Zihuantanejo, Guerrero, December 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.

The Mexican Redknee Tarantula, Brachypelma smithi, is a member of the Theraphosidae Family of Hairy Spiders. The Theraphosidae Family consists of 988 members placed into 147 genera. The Brachypelma genus consists of 18 species. This species is often confused with Brachyphelma hamorii because they have both been referred to as Mexican Redknee Tarantulas. The Mexican Redknee Tarantula is known in Mexico as Tarántula de Rodilla Roja

Mexican Redknee Tarantulas are covered in long, brown hairs. They have four pairs of legs on their cephalothorax, one pair of pedipalps, and hollow fanged chelicerae that are attached to venom glands. They use their first two legs to hold and catch prey, and the rest are used to walk. Hairs on their legs allow them to sense vibrations and their pedipalps allow them to smell, taste, and feel. Each foot has two claws which enable them to climb slippery surfaces. Their abdomen is black with two pairs of spinnerets on the posterior side. Their legs are black with orange-red joints, giving them their name. Sexual dimorphism is displayed with females growing larger and having slightly different coloration than the males. Adult males have an orange carapace, while adult females have an almost black carapace with orange around the border. Males can grow up to 4.6 cm (1.8 inches) in length (not including chelicerae and spinnerets), while females being larger that reach a maximum of 5.6 cm (2.2 inches) in length. 

Mexican Redknee Tarantulas are nocturnal and fossorial, burrowing under large angular rocks and tree roots. There are no traces of silk at their burrow entrance and the interior is often multi-tunnelled, especially if populations occur on rocky slopes. Their abandoned burrows also make good retreats for venomous snakes and ground-nesting wasps. Mexican Redknee Tarantulas are polygynandrous. Mating occurs near the female’s burrow during the end of the rainy season and first part of the dry season, between September and January. Before copulation, the male weaves a special web on which he deposits sperm. The male and female face each other and the female opens her jaws wide. The male then uses a special pair of spurs on his front legs to lock her jaws open, before the pair push each other into a reared-back position. With his second set of legs, the male holds the female down and bends her backwards. The male then transfers his sperm to the female’s opisthosoma, a small opening on the underside of the abdomen. Finally, the male releases one of the female’s fangs and positions himself to flee, as the females are known to be aggressive to males after mating. The females store the sperm and eggs inside their bodies until the spring. At this time, females lay 200 to 400 eggs on a silk mat that they have made and covered with a sticky liquid containing the sperm. Fertilization occurs within minutes. The eggs are then wrapped in silk and collected into an egg-sac, which is carried by the mother between her fangs. Egg-sacs may also be placed in hollows, beneath rocks, or in natural debris. Females guard their egg sacs, turn them, and move them around to ensure the appropriate humidity and temperature are maintained. While the eggs hatch in approximately nine weeks, the spiderlings will remain in the egg-sac for another three weeks after hatching. After emerging from the egg sac, the spiderlings remain in the burrow with their mother for an additional two weeks. Males reach sexual maturity at approximately four years of age and live up to ten years, while females mature at six to seven years of age and live twenty-five to thirty years. Captive individuals mature faster than those in the wild. Like many tarantulas, the Mexican Redknee Tarantulas grow slowly. Spiderlings molt every two weeks for the first four months, and less frequently thereafter. While males do not molt after reaching sexual maturity, females will continue to molt infrequently. Molting removes any external parasites or fungus and provides new, undamaged sensory and protective hairs. 

Mexican Redknee Tarantulas are primarily ambush predators and remain in their burrows, waiting for unsuspecting prey to walk across their web. They consume large insects, frogs, and mice. Once prey is detected, they rush out and hold the prey down with their front legs while biting them. Their bite injects a venom into their victims that paralyzes and liquifies them. The juices of the prey are then consumed, while the undigested body parts are typically wrapped up in a web and transported to another area of the burrow. In turn, the Mexican Redknee Tarantula is preyed upon by birds, lizards, snakes, and parasitic wasps. When threatened by large predators, they can flick or drop barbed hairs off of their abdomen. These hairs dig into the skin and can cause an irritating rash. If the hairs penetrate an organism’s eyes, they can cause blindness.  They inhabit dry thorn forests and deciduous forests, living within dense thickets or vegetation. They appear to prefer undisturbed areas shaded by trees or bushes.

Brachypelma smithi is often confused with Brachyphelma hamorii due to their similar appearances and shared common name of Mexican Redknee Tarantula. These species can be differentiated by distinct physical characteristics. Brachyphelma smithi has brighter orange colorations and the lateral hairs along the length of their legs are yellowish. Conversely, Brachyphelma hamorii has whitish lateral hairs along the length of their legs, providing greater contrast with the darker areas. 

From a conservation perspective, the Mexican Redknee Tarantula is considered to be Near Threatened as its populations are believed to be in decline attributed to loss of habitat. Additionally, they have an estimated extent of occurrence (EOO) of less than 20,000 km2 (7,700 mi2). Urbanization and related transport infrastructure are rapidly expanding in the southern coastal region of their range, threatening and destroying several subpopulations. Roads are another threat for populations along the north-south coastal highway, since males are killed by cars while crossing it during the mating season. Mexican Redknee Tarantulas are also heavily affected by overharvesting for use in traditional medicine, especially in the Pacific coastal area of Guerrero State. Some populations in the highlands have been depleted by locals, and others have been depleted by smugglers for the pet trade. While captive populations of this species are reared and sold legally, there is still a large unknown amount of illegal trafficking. Unfortunately their populations are easily accessible by smugglers, increasing overharvesting. In some cases, a single smuggler can catch over a hundred specimens. They are traded internationally to the United States, Canada, Europe, and Asia.