This venomous but docile tarantula is the most common spider used in movies due to its large size and beautiful colouration. A particularly striking tarantula, the Mexican redknee has a dark brown body and legs, with orange-red leg joints (3). The ends of the legs can detect vibrations, smells and tastes, to help the tarantula locate prey and the opposite sex, although it also has a group of eight eyes on the top of the carapace (4).

In the wild, Mexican redknee tarantulas mate in the summer, shortly after the male's maturing moult, usually in the rainy season (July and August) (7). Mating occurs in or near to the female's burrow, where the male uses his pedipalps (front limbs) to transfer his sperm into openings in the underside of the female's abdomen. After mating, some females will try to kill and eat the male, although this has never been observed in the wild (7). The sperm and eggs are stored in the female's body and not laid until spring. In the spring, the female deposits hundreds of eggs and the sperm onto a silk mat which she has made and then fashions this mat into a ball or egg sac. Fertilisation takes place within minutes and the spiderlings hatch in just less than three months (7), but the spiderlings remain in the egg-sac for a further three weeks. Once out of the egg-sac they spend two weeks in the burrow before dispersing. Males mature at about four years of age and females two to three years later at about six or seven years old (3). They are a long-lived species with females living up to 25 to 30 years old (4); however males only live about one year after maturity (7). Hunting at night by lying in ambush, the Mexican redknee tarantula attacks insects, small frogs, small lizards, and mice. An area on the end of each leg is sensitive to smells, tastes and vibrations, and this is used to detect prey. The tarantula holds its prey with its pedipalps (front limbs) and injects it with venom delivered via two hollow fangs. This venom has a double purpose, paralysing the prey as well as beginning digestion. Once the venom has acted, the tarantula is able to suck up the proteins and fats of its prey, leaving just a small ball of undigested body parts (4). This usually docile tarantula will kick hairs off the abdomen with its hind legs when threatened, which cause blindness if they hit the eyes of a predator and can also cause a rash on the skin (4).

Mexican redknee tarantulas are found along the central Pacific coast of Mexico, from southern coastal Jalisco to north-western Oaxaca State and inland to the states of Mexico and Morelos (5).

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

Systems

• Terrestrial

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

Lives in ground burrows (6), in rocky areas under thorny vegetation, usually in scrubland or desert, dry thorn forest or tropical deciduous forest (4) (5).

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

Commensal/Parasitic 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.

Known Predators:

• birds Aves
• moths Lepidoptera
• lizards Squamata

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.

Typical lifespan

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

The Mexican redknee tarantula is classified as Lower Risk / Near Threatened (LR/nt) on the IUCN Red List 2007 under the name Euathlus smithi (1), and is listed on Appendix II of CITES (2).

This particular species is the most popular captive tarantula species in the world, and prior to 1985 it was collected in thousands (6). Habitat loss is now the major threat to the Mexican redknee tarantula.

Conservation Actions

Listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) in 1985, the Mexican redknee tarantula can now only be traded internationally according to quotas and with trade permits (6), and in Mexico permits are required to collect or remove any spider from the Theraphosid family (5).

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