Mexican red-knee tarantulas are large, dark spiders that range from 12.7 to 14 cm in length. They have a black abdomen that is covered in brown hairs. Their legs have orange to dark red-orange joints, giving them their name. Their carapace is creamy beige in color and has a distinctive black square. The cephalothorax has four pairs of legs, a pair of pedipalps, and hollow fanged chelicerae connected to venom glands. They hold and catch prey with the first 2 legs and walk with the other legs. There are 2 pairs of spinnerets on the posterior side of their abdomen. Adult males have special copulatory organs located on their pedipalps. Females are generally larger than males.
Range length: 12.7 to 14 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; venomous
Sexual Dimorphism: female larger
Mexican red-knee tarantulas reside in dry areas with little vegetation, usually in scrubland, deserts, dry thorn forests, or tropical deciduous forests. They live in burrows in rocky areas at the base of thorny vegetation like cacti. Burrows usually have one entrance that is a little wider than the tarantula itself. A web carpet extends from the burrow out of the opening but is usually covered or coated in the substrate of the area. When the burrow is in use, silk can be found near the entrance. During the reproductive season, extra silk is present in the burrows of mature females.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest ; scrub forest
Habitat and Ecology
Mexican red-knee tarantulas prey on large insects, frogs and mice. Mexican red-knee tarantulas remain in their burrow, waiting to ambush prey that walk across their web. Prey are detected using palps on the end of each leg, which are sensitive to smell, taste, and vibrations. Once they detect their prey, Mexican red-knee tarantulas rush out to bite prey and return to the burrow. They hold down their pray with their front legs and inject their venom to paralyze and liquefy their victims. They consume the juices of their prey, leaving behind undigested body parts. These are typically wrapped up in a web and transported to another area of the burrow.
Animal Foods: mammals; amphibians; body fluids; insects
Primary Diet: carnivore (Eats terrestrial vertebrates, Eats body fluids, Insectivore )
As generalists, Mexican red-knee tarantulas do not control species of prey. As a whole, however, tarantulas help stabilize or regulate insect populations, as tarantulas are one of the biggest families of insectivores and exhibit a wide variety of lifestyles and foraging strategies. Spiders are also important prey for birds, moths, lizards, and other insectivores. Spiders are primary food sources for bark-gathering birds. Birds also use the silk of spiders to build nest, as the protein fibers of their silk adds stability.
Mexican red-knee tarantulas are parasitized by pepsis wasps, which use their body as a nest. Pepsis wasps seek tarantula burrows and vibrate their body, mimicking prey. When a tarantula emerges from its burrow, the wasp stings it and lays eggs in its paralyzed body. When the larvae hatch, they feed upon the tarantula.
Ecosystem Impact: keystone species
- Pepsis wasps Pepsinae
Mexican red-knee tarantulas are preyed upon by birds, moths, lizards, and other insectivores. When threatened by large predators, Mexican red-knee tarantulas can flick or drop hairs off of their abdomen. These "urticating" hairs are barbed and dig into the skin, causing irritation or a painful rash. If the hairs penetrate an organism's eyes, they can cause blindness.
- birds Aves
- moths Lepidoptera
- lizards Squamata
Life History and Behavior
Mexican red-knee tarantulas have eight eyes located around their head so they can see both forward and backward. However, their vision is relatively poor. Hairs on their legs are used to sense vibrations, and the palps on the end of their legs allow them to smell, taste, and feel. Each foot has two claws, enabling the spider to climb slippery surfaces.
Communication Channels: visual ; tactile
Other Communication Modes: vibrations
Perception Channels: visual ; vibrations ; chemical
Mexican red-knee tarantulas, like many tarantulas, grow slowly. Females wrap fertilized eggs in silk and carry the egg-sac between her fangs. After 1 to 3 months, the eggs hatch. Spiderlings molt every 2 weeks for the first 4 months, and less frequently after that. Males do not molt after reaching sexual maturity at 4 to 5 years of age. Females, though infrequently, continue to molt after reaching sexual maturity at 6 to 7 years of age. Molting removes any external parasites or fungus and provides new undamaged sensory and protective hairs.
Female Mexican red-knee tarantulas typically live 25 to 30 years while males rarely live more than 10 years.
Status: wild: male 10 years; female 30 (high) years.
Mexican red-knee tarantulas mate shortly after the male's maturing molt. Before copulation, males weave a special web on which he deposits sperm. Mating occurs near the female's burrow. The male and female face each other, and the female opens her jaws wide. The male uses a special pair of spurs on his front legs to lock her jaws open. They then push each other into a reared-back position. With second set of legs, the male holds the female down and bends her backwards. The male then collects his sperm with his pedipalps and transfers it to the female's opithosoma, a small opening on the underside of the abdomen. The male releases one of the female's fangs, positioning hims legs for retreat. After mating, males generally flee, as females are known to be aggressive to males after mating. Some females may try to kill and eat the male, although this has not been observed in the wild. Mexican red-knee tarantulas are polygynandrous.
Mating System: polygynandrous (promiscuous)
Mexican red-knee tarantulas mate soon after the male's maturing molt, which usually happens between July and October during the rainy season. Females store the sperm and eggs in her body until the spring. Females make a silk mat, on which she lays 200 to 400 eggs, which she covers with a sticky liquid containing the sperm. Fertilization occurs in minutes. The eggs are wrapped in silk and collected into a ball or egg-sac. Females carry the egg-sac between their fangs. Eggs hatch in 1 to 3 months, though spiderlings remain in the egg-sac for another 3 weeks after hatching. After leaving the egg-sac, spiderlings spend another 2 weeks in their burrow before they disperse. They reach independence at this point, usually at 12 to 16 days of age. Males reach sexual maturity at approximately the 20th instar (the stage between molts that comes at about 4 years of age). Females mature 2 to 3 years later than males, at 6 to 7 years of age. In captivity, Mexican red-knee tarantulas mature more quickly than in the wild.
Breeding season: Mexican red-knee tarantulas typically mate between July and October, usually in the rainy season.
Range number of offspring: 200 to 400.
Average gestation period: 9 weeks.
Range time to independence: 12 to 16 days.
Range age at sexual or reproductive maturity (female): 6 to 7 years.
Average age at sexual or reproductive maturity (male): 4 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Female Mexican red-knee tarantulas wrap their eggs in a silk egg-sac and carry them between their fangs. Egg-sacs may also be placed in hollows between or beneath rocks or natural debris. A female guards her egg-sac, turns it, and moves it around to ensure appropriate humidity and temperature are maintained. Eggs hatch in approximately 9 weeks, though spiderlings remain in the egg-sac for another 3 weeks. After emerging from the egg-sac, they remain in the burrow with their mother for an additional 2 weeks. Mothers guard their offspring until they disperse around 12 to 16 days of age.
Parental Investment: precocial ; female parental care ; pre-hatching/birth (Protecting: Female); pre-independence (Protecting: Female)
Mexican red-knee spiders are considered "near threatened" by the IUCN and are on Apendex II of CITES, which limits trade of individuals between countries. It is illegal to catch and sell wild individuals. Mexican red-knee spiders are at risk because of the pet trade and habitat destruction.
US Federal List: no special status
CITES: appendix ii
IUCN Red List of Threatened Species: lower risk - near threatened
IUCN Red List Assessment
Red List Category
Red List Criteria
- Needs updating
- 1994Insufficiently Known(Groombridge 1994)
- 1990Insufficiently Known(IUCN 1990)
- 1988Insufficiently Known(IUCN Conservation Monitoring Centre 1988)
- 1986Insufficiently Known(IUCN Conservation Monitoring Centre 1986)
Relevance to Humans and Ecosystems
Mexican red-knee tarantulas are generally docile and do not harm humans. However, when threatened, they can shoot their urticating hairs for defense, which can cause irritation. Their bite, while venomous, is not fatal and can cause pain equivalent to a bee or wasp sting. Some individuals are allergic to spider venom and have more severe reactions.
Negative Impacts: injures humans (bites or stings, venomous )
Because they are docile and colorful, Mexican red-knee tarantulas are popular in the pet trade, generating considerable income. They are also kept in many zoological institutions. Mexican red-knee tarantulas are commonly used in Hollywood films, as well.
Positive Impacts: pet trade
Mexican redknee tarantula
Mexican red-kneed tarantula (Brachypelma smithi) is a terrestrial tarantula native to the western faces of the Sierra Madre Occidental and Sierra Madre del Sur mountain ranges in Mexico. They are a large species, and are a popular choice for enthusiasts. Like most tarantulas, they have a long lifespan.
The mature Brachypelma smithi has a dark-colored body with orange patches on the joints of its legs. The second element of the legs is orange-red. Following molting, the colors are more pronounced. The dark portion is very black while the orange-red portions will be far more on the reddish side.
An adult male has a body roughly 4 inches long, with a leg span of 6 inches, and a mass of approximately 15 grams. Both sexes are similar in appearance, with the male having a smaller body, but longer legs. Though the male is of comparable size to the female, the male has a much smaller mass.
The Mexican Red Knee grows very slowly and matures relatively late. The females of this species can live up to 30 years, but the males tend to live for only 5 or so years.
Like all tarantulas, the Mexican red knee is an arthropod, and must go through a molting process in order to grow. It is an essential part of their life process. Molting serves several purposes, such as renewing the tarantula's outer cover (shell) and replacing missing appendages. As tarantulas grow they will regularly molt (shed their skin), on multiple occasions during the year, depending on the tarantula's age. Since the exoskeleton cannot stretch, it has to be replaced by a new one from beneath. A tarantula may also regenerate lost appendages gradually, with each succeeding molt. Prior to molting the spider will become sluggish and stop eating in order to conserve as much energy as possible. Their abdomen will darken; this is the new exoskeleton beneath. Normally the spider will turn on its back to molt and lie still in that position for several hours. Once this has been accomplished, the tarantula will not eat for several days to weeks, and it is not uncommon for them to not eat for up to a month or more after a molt, as its fangs are still soft: the fangs are also part of the exoskeleton and are shed with the rest of the skin. The whole process can take several hours and sheathes the tarantula with a moist new skin in place of an old, faded one.
Like most New World tarantulas, they will kick urticating hairs from their abdomens and their back legs if disturbed, rather than bite. They are only slightly venomous to humans and are considered extremely docile, though, as with all tarantulas, allergies may intensify with any bite.
They carve deep burrows into soil banks, which keeps them protected from predators, like the white-nosed coati, and enables them to ambush passing prey. The females will spend the majority of their lives in their burrows. The burrows are typically located in or not far from vegetation and consists of a single entrance with a tunnel leading to one or two chambers. The entrance is just slightly larger than the body size of the spider. The tunnel, usually about three times the tarantula's leg span in length, leads to a chamber which is large enough for the spider to safely molt in. Further down the burrow, via a shorter tunnel, a larger chamber is located where the spider will rest and eat its prey. When the tarantula needs privacy, e.g. when molting or laying eggs, the entrance is sealed with silk sometimes supplemented with soil and leaves.
Their natural habitat is in deciduous tropical forests in the hilly southwestern Mexico, especially in Colima and Guerrero. In 1985 the species was listed as endangered by CITES because the wild-caught specimens shipped for the Chinese market were decreasing in size. The smaller sizes were suspected to be a consequence of a declining population due to excessive export. Exporting is not the only threat however; some local people have reportedly made a habit of killing these spiders in a nearly systematic way using pesticides, pouring gasoline into burrows or simply killing migrating spiders on sight. The reasons for these actions seem to be an irrational fear based on myth surrounding B. chinese and related species. Thus, whether the listing strengthened the B. smithi wild population or not remains uncertain. The species has nonetheless been bred successfully in captivity, making them readily available on the pet market despite almost no export of wild-caught spiders from Mexico.
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- Locht, A.; Yáñez, M.; Vázquez, I. (1999). "Distribution and Natural History of Mexican Species of Brachypelma and Brachypelmides (Theraphosidae, Theraphosinae) with Morphological Evidence for Their Synonymy". The Journal of Arachnology 27: 196–200.
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