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Brachypelma smithi

By Amanda Giesler and David Zaitz

Geographic Range

Mexican red-knee tarantulas, Brachypelma smithi, are primarily found along the central Pacific coast of Mexico. ("Mexican Red Knee Tarantula", 2009; West, 2009)

Habitat

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. (Locht, et al., 1999; "Mexican Red Knee Tarantula", 2008; West, 2009)

Physical Description

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. ("Mexican Red Knee Tarantula", 2008; "Mexican Red Knee Tarantula", 2008)

  • Sexual Dimorphism
  • female larger
  • Range length
    12.7 to 14 cm
    5.00 to 5.51 in

Development

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. ("Mexican Red Knee Tarantula", 2008; "Phylum Arhropoda", 2002; West, 2009)

Reproduction

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. ("Bio Facts: Red Kneed Tarantula", 2008; Moya-Larano, et al., 2003; "Mexican Red Knee Tarantula", 2008; West, 2009)

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. ("Bio Facts: Red Kneed Tarantula", 2008; Moya-Larano, et al., 2003; "Mexican Red Knee Tarantula", 2008; West, 2009)

  • 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

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. ("Bio Facts: Red Kneed Tarantula", 2008; "Mexican Red Knee Tarantula", 2008; West, 2009)

Lifespan/Longevity

Female Mexican red-knee tarantulas typically live 25 to 30 years while males rarely live more than 10 years. ("Bio Facts: Red Kneed Tarantula", 2008; Locht, et al., 1999; "Mexican Red Knee Tarantula", 2009; "Mexican Red Knee Tarantula", 2008; West, 2009)

  • Typical lifespan
    Status: wild
    male 10 years; female 30 (high) years

Behavior

Mexican red-knee tarantulas are generally docile. When threatened, they rear up to display their fangs. They can also flip barbed hairs off of their abdomen as a defense. Mexican red-knee tarantulas are often aggressive toward rogue spiders, which may be in response to competition. ("Mexican Red Knee Tarantula", 2008; Orkin, Inc., 2009; West, 2009)

Home Range

Little information is available regarding the home range of Mexican red-knee tarantulas. (Locht, et al., 1999)

Communication and Perception

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. ("Mexican Red Knee Tarantula", 2008)

Food Habits

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. (Locht, et al., 1999; "Mexican Red Knee Tarantula", 2009; "Mexican Red Knee Tarantula", 2008)

  • Animal Foods
  • mammals
  • amphibians
  • body fluids
  • insects

Predation

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. ("Mexican Red Knee Tarantula", 2009; "Mexican Red Knee Tarantula", 2008; Orkin, Inc., 2009)

Ecosystem Roles

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. (Hansel, 1993; Nyffeler, et al., 1994; Peterson, et al., 1989; Riechert and Lockley, 1984; Skerl, 1997)

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. ("Mexican Red Knee Tarantula", 2009; Peterson, et al., 1989)

Commensal/Parasitic Species
  • Pepsis wasps Pepsinae

Economic Importance for Humans: Positive

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. (Locht, et al., 1999; "Mexican Red Knee Tarantula", 2009; "Mexican Red Knee Tarantula", 2008; West, 2009)

Economic Importance for Humans: Negative

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. ("Mexican Red Knee Tarantula", 2009; Orkin, Inc., 2009)

  • Negative Impacts
  • injures humans

Conservation Status

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. (Cites, 2009; IUCN, 2009; "Mexican Red Knee Tarantula", 2009; "Mexican Red Knee Tarantula", 2008)

Contributors

Amanda Giesler (author), Rutgers University, David Zaitz (author), Rutgers University, David V. Howe (editor), Rutgers University, Gail McCormick (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Jacksonville Zoo & Gardens. 2008. "Bio Facts: Red Kneed Tarantula" (On-line). Jacksonville Zoo. Accessed November 10, 2009 at http://www.jaxzoo.org/animals/biofacts/RedkneedTarantula.asp.

Nashville Zoo at Grassmere. 2009. "Mexican Red Knee Tarantula" (On-line). Nashville Zoo at Grassmere. Accessed November 10, 2009 at http://www.nashvillezoo.org/animals_detail.asp?animalID=45.

Oakland Zoo. 2008. "Mexican Red Knee Tarantula" (On-line). Oakland Zoo. Accessed November 10, 2009 at http://www.oaklandzoo.org/animals/arthropods/mexican-red-knee-tarantula.

Sea Studios Foundation. 2002. "Phylum Arhropoda" (On-line). The Shape of Life. Accessed November 11, 2009 at http://www.pbs.org/kcet/shapeoflife/animals/arthropods.html.

Cites, 2009. "Cites Species Database" (On-line). Cites Species Database. Accessed November 10, 2009 at http://www.cites.org/eng/resources/species.html.

Hansel, M. 1993. Secondhand silk. Natural History, 10: 40-46.

IUCN, 2009. "Euathlus smithi (Red Kneed Tarantula)" (On-line). The IUCN Red List of Endangered Species. Accessed November 10, 2009 at http://redlist.org/apps/redlist/details/8152/0.

Locht, A., M. Yanez, I. Vasquez. 1999. Distribution and natural history of Mexican species of Brachypelma and Brachypelmides (Theraphosidae, Theraphosinae) with morphological evidence to support their synonymy. The Journal of Arachnology, 27(1): 196-200.

Moya-Larano, J., J. Pascual, . Wise. 2003. Mating patterns in late-maturing female Mediterranean tarantulas may reflect the costs and benefits of sexual cannibalism. Animal Behaviour, 66(3): 469-476. Accessed November 11, 2009 at http://www.uic.edu/depts/ovcr/iesp/Publications/Faculty%20Publications/Wise/Moya-Larano%20J%20et%20al%202003%20Anim%20Behav_Mating%20Patterns.pdf.

Nyffeler, M., W. Sterling, D. Dean. 1994. How spiders make a living. Entomological Society of America, 23(6): 1357-1367.

Orkin, Inc., 2009. "The Mexican Red Knee Tarantula’s Predators" (On-line). Orkin, Inc.. Accessed November 10, 2009 at http://www.orkin.com/other/spiders/the-mexican-redknee-tarantulas-predators.

Peterson, A., D. Osborne, D. Taylor. 1989. Tree trunk arthropod faunas as food resources for birds. Ohio Journal of Science, 89(1): 23-25.

Riechert, S., T. Lockley. 1984. Spiders as biological control agents. Annual Review of Entomology, 29: 299-320.

Skerl, K. 1997. "Spider Conservation in the United States" (On-line). University of Michigan. Accessed November 11, 2009 at http://www.umich.edu/~esupdate/library/97.03-04/skerl.html.

West, R. 2009. "Mexican Red Kneed Tarantula" (On-line). Arkive. Accessed November 10, 2009 at http://www.arkive.org/mexican-redknee-tarantula/brachypelma-smithi/info.html.

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