Common Name: Orange Kneed Tarantula
Latin Name: Brachypelma smithi
Family: Theraphosidae
Genus: Brachypelma

Range and Abundance
Brachypelma s. are indigenous to Central and South American, however there are hundreds of tarantula species that are found around the globe in tropical and subtropical regions. They also range in behavior and morphology based on elevation levels. This specific species is found in lower elevation areas, like La Selva Biological Research Station in Costa Rica. They are not commonly seen during the day because they are nocturnal, however they have been known to emerge from their nests at dusk.

Brachypelma s.,is very unique and distinctive coloration. It has a black body, but possess distinctive orange bands that wrap around its legs and lower abdomen.

The Brachypelma s. shares a very similar morphology to the Theraphosidae family; they are large, hairy and mildly poisonous. However, their venom is mild and is comparably weaker than honeybees and is therefore harmless to humans. The stark difference between the Brachypelma s.and other tarantula species is that they are three times smaller than the average sized tarantula. They grow to about the size of a human hand and they only weigh a few grams.

The Brachypelma s. uses its front legs as a sensory system, similar to the antenna of an ant, to scour the forest floor. Even though the spider has many eyes it actually utilizes these leg antennae the most when searching for pray. These legs are smaller than the other eight and they grow out right next to its mouth.

The Brachypelma s. possesses signs of sexual dimorphism. The males sometimes can have a more gray and brown colored body and have faded orange bands around there legs. The females usually have bright orange bands and very black dark body coloring. The males also have more hook like front legs in order to secure the female in position to mate.

Reproductive cycle
The male tarantula mates by spinning a web and then injecting sperm along the lining of the web. They wait for the female and then scurry away (sometimes the females will eat the male). The female rubs its lower abdomen up against the web to become impregnated and proceeds to lay 500 to 1,000 eggs per reproductive event. They encase the eggs and sperm in a reproductive cocoon and wait size to nine weeks for the eggs to hatch. They can live up to 20 years and they reach full maturity in 5 years. As they grow they will molt their external skeleton. During this process they can also re-grow stomach lining, genetalia and any lost limbs.

The tarantula has been known to nest in all levels of the rainforest however the majority of them will find a home on the ground. Unlike other spiders tarantulas usually build nests rather than webs. They will make their homes under loose leaves or tree bark, others will find ground living in epiphytes. However, most of their burrows are made of leaf litter collected over the forest floor. They line these nests with a protective silk covering that they create with their feet.

The South American bird-eating spider (Theraphosa blondi) has been known to prey on tarantulas. These birds have a leg span of 18cm and commonly find and eat these spiders, the bigger they are the bigger the meal they get. (This may be a reason why these tarantulas are smaller than other tarantulas). An advantage to these smaller tarantulas they are more agile and camouflaged then others and this may provide a greater means of protection.

Since they are nocturnal they mate and hunt at night. They are very shy creatures and even though they have a venomous bite, they will not bite unless provoked. They only will use venom if they feel like they are trapped, in real danger, or hunting prey because it takes a while for them to replenish their supply. Their venom is not fatal, (comparable to a honeybee) but it can be very painful and many times leaves a nasty deep mark on your skin. Before it bites, as a defense, it may use its back legs to flick off urticating hairs that are located on the back of its abdomen. The hairs can sting if they come into contact with the eyes or mouth. Another aggressive warning behavior that they show is rearing up on their back legs like a horse and hissing.

Brachypelma s. usually eats other arthropods, smaller spiders, ants, beetles ext that are smaller than themselves.

There are some symbiotic relationships with toads and tarantulas however the ones we would encounter in Costa Rica do not have any known symbiotic relationships. The spiders will use the compounds found in the skin of toads as a way to protect it-self against infestations and parasites. The Tarantula will then protect the toad against predators for the resource.
There are also a few wasp species that will paralyze the tarantula and lay its eggs on its back. When the eggs hatch they larvae are able to climb out and eat the living tarantula. However, there are no known interactions between wasps and the orange-kneed tarantula in particular.


Costa Rica :
We found this species on a tree trunk during our second night walk. We believed that the Tarantula was male because its coloration was more faded. The spider did not move while we were watching however, it could have been stunned by the light that we were shining on it or it could have been hunting. In one photo we captured a shot of a grasshopper sitting on a branch not too far away from the tarantula. We assumed that the tarantula could have been on a preditorial pursuit of the grasshopper. We also noted that it was rare for the tarantula to be this high up on the tree because their nest is on the ground. They also forage regularly on the ground. Otherwise It was really interesting have the opportunity to see this spider in its natural habitat.

Work Cited:

Gorb, Stanislav N., Senta Niederegger, Cheryl Y. Hayashi, Adam P. Summers, Walter Vötsch, and Paul Walther. "Biomaterials: Silk-like Secretion from Tarantula Feet." Nature 443.7110 (2006): 407. Print.

Janowski-Bell, Margaret E., and Norman V. Horner. "Movement of the Male Brown Tarantula, Aphonopelma Hentzi (Araneae, Theraphosidae), Using Radio Telemetry." American Arachnological Society 27.2 (1999): 503-12. Print.

Locht, A., M. Yanez, and I. Vasquez. "Distribution and Natural History of Mexican Species of Brachypelma Adn Brachypelmides (Theraphosidae, Theraphosina) with Morphological Evidence for Their Synonymy." The Journal of Aachnology 27 (1999): 196-200. Print.

Punzo, Fred. "The Biology of the Spider WAsp, Pepszs Thisbe (Hymenoptera:Pompilidae) From Trans Pecos, Texas. I. Adult Morphometrics, Larval Development and the Ontogeny of Larval Feeding Patterns." Psyche 101 (1994): 229-42. Print.

"Tarantula; Aphonopelma Chalcodes." National Geographic. Natrional Geographic Society, 2012. Web. 28 Apr. 2012. <http://animals.nationalgeographic.com/animals/bugs/tarantula/>.