Genus of spiders
Brachypelma is a genus of spiders in the family Theraphosidae (tarantulas). They may have bodies up to long with legs of similar or greater lengths. Some species have brightly colored legs, with red or orange marks and rings.
The taxonomy of the genus and its species has been the subject of considerable debate. In 2020, the genus was split, with a group of species (the "red rump" tarantulas) being moved to a new genus, "Tliltocatl". As now circumscribed, the genus "Brachypelma" is found only in Mexico. Many species of both genera are popular with tarantula keepers as pets; the females in particular are long lived. All species are protected, and trade is regulated under CITES. Although they are bred in captivity, they continue to be exported in large numbers. Members of the reduced genus "Brachypelma" (the "red leg" group) are considered to be in most urgent need of further conservation efforts.
Description.
Members of the family Theraphosidae, the tarantulas, to which "Brachypelma" belongs, are generally large compared to other spiders, and are commonly seen as "objects of dread". Tarantulas do not use webs for capturing their prey, relying on their venom and their size and strength. "Brachypelma" species are noted for their large size, colorfulness and docility in captivity. Larger species of "Brachypelma", such as "B. smithi", have body lengths in the approximate range with legs up to long. Females on average have longer bodies than males but shorter legs.
Species have bright red markings on their legs. "B. boehmei" has been described as the "most gorgeous" species of the genus. The parts of the legs closest to the body are black, then three segments (the patellae, tibiae and metatarsi) are bright orange-yellow, followed by black tarsi. Although brightly colored, "Brachypelma" species are cryptic when in their native habitat.
Diagnosis.
The distribution of hairs on the legs and palp and the shape of the male and female genitalia are the diagnostic features of the genus. In common with species of "Tliltocatl", the prolateral (forward facing) surface of the trochanter and femur of the first leg and the retrolateral surface of the pedipalp have plumose hairs, and there is no pad of plumose hairs on the femur of the fourth leg. The male palpal bulb has a flattened, spoon-shaped embolus; females have fused spermathecae, with a flat cross-section. "Brachypelma" can be distinguished from "Tliltocatl" by presence of the red or orange patterns on the legs of all species except "B. albiceps", which can be recognized by the golden yellow carapace. "Brachypelma" species lack spines on the patellae of the pedipalps and legs, unlike "Tliltocatl" species. The shape of the genitalia differs between the genera; the apex of the male palpal bulb is shorter in "Brachypelma" and the female spermatheca baseplate is more strongly developed and hardened.
Life history.
All the species of "Brachypelma" that have been studied in detail live in burrows. These have a single entrance, a little larger than the spider, opening into a horizontal tunnel that usually leads to two chambers: one where it molts and one where it rests and consumes its prey. The entrance is blocked with material, such as soil and leaves, bound together by silk when the spider is inactive for significant length of time; otherwise the entrance is open with some silk visible. North American tarantulas like "Brachypelma" are "sit and wait" predators, seizing prey passing by the burrow entrance.
Compared to related genera, "Brachypelma" species are long-lived. The maximum life-span recorded in two Berlin zoos was 12 years for "Brachypelma annitha" (now a synonym of "B. smithi"). In the wild, females take around 9–10 years to reach maturity, but can then live for another 10 years. Males can take 7–8 years to reach maturity, afterwards usually dying within a year, probably because when mature they actively seek mates and rarely feed while doing so, whereas females remain around their burrows.
Studies on species in the wild showed that pre-adult and adult spiders molt towards the end of the dry season, which lasts from June to November. After their last molt, adult males search for females, travelling in the daytime, particularly in the morning and evening. Females produce an egg sac before they molt. The eggs hatch a few weeks before the rainy season begins. The spiderlings molt every two weeks for the first few months, then less frequently as they mature. A full-grown "Brachypelma" may molt as infrequently as once a year.
Taxonomy.
The genus "Brachypelma" was erected by Eugène Simon in 1891 for the species "Mygale emilia", originally described in 1856. "Brachypelma" is derived from the Greek (brachys), meaning 'short' and (pelma) meaning 'the sole of the foot'. However, arachnologists have conventionally taken "pelma" to refer to the tarsal scopula, producing the overall meaning '(with) short scopula'. (See also Tarantula § The element "pelma" in genus names.)
The genus has not always been recognized. In 1897, Frederick Pickard-Cambridge considered "Brachypelma" to be a synonym of "Eurypelma", regarding the two as not distinct from one another. ("Eurypelma" is now a synonym of "Avicularia".) In 1903, Reginald Pocock recognized "Brachypelma", listing four species and noting that there were more. Other arachnologists, like Robert Raven in his 1985 monograph of Mygalomorphae, treated "Brachypelma" as a synonym of "Euathlus". In 1992, Günter Schmidt clarified the difference between "Euathlus" and "Brachypelma", resulting in the latter's acceptance as a distinct genus.
The genus "Brachypelmides", erected by Schmidt and Krause in 1994, is considered a synonym of "Brachypelma" by some sources, including the World Spider Catalog, although this has been rejected by Schmidt. When broadly defined, "Brachypelma" is distinguished from related genera by the plumose setae (hairs) on the prolateral (forward-facing) side of the trochanter and femur of the first leg and on the retrolateral (outward-facing) side of the pedipalp.
A 2017 study concluded that the genus "Brachypelma" as then circumscribed was not monophyletic, and that only eight "red leg" species belong in "Brachypelma" sensu stricto, the remaining species (the "red rump" group) being misplaced. In 2020, they were transferred to the new genus "Tliltocatl".
DNA barcoding.
In 2017, Mendoza and Francke applied DNA barcoding to some Mexican species of "Brachypelma". In this approach, a portion of about 650 base pairs of the mitochondrial gene cytochrome oxidase I (COI) is used, primarily to identify existing species, but also sometimes to support a separation between species. One cladogram resulting from the DNA barcodes is shown below. Although "B. hamorii" and "B. smithi" are very similar in external appearance and have not always been treated as separate species, they are clearly distinguished by their DNA barcodes. All the species in the cladogram below belong to "Brachypelma" sensu stricto (the "red leg" group).
Phylogeny.
In 2017, Steven Turner and colleagues reported on a phylogenetic analysis of the family Theraphosidae based on mitochondrial DNA. A cladogram based on Bayesian analysis of a sample within their proposed tribe Theraphosini is shown below, with current genus names added.
The cladogram shows that the genus "Brachypelma" as then circumscribed was not monophyletic, but fell into two distinct clades. All analyses supported the view that "Brachypelma" (along with "Aphonopelma") was made up of deeply divergent subgroups. Detailed analysis further suggested that the species in the "red rump" group were closely related, with several supposed species, particularly those labeled "Brachypelma vagans" (now "Tliltocatl vagans") not being monophyletic. The authors cautioned that the necessary use of specimens obtained through the commercial pet trade meant that their exact geographical origins were often unknown, leading to uncertainty as to their identification. Subsequently, a new genus "Tliltocatl", was erected for the "red rump" group.
Species.
As of March 2020[ [update]], the World Spider Catalog accepted only the species listed below. All other species formerly placed in "Brachypelma" have been transferred to other genera, most to "Tliltocatl".
Two species have been moved to the genus "Sericopelma":
Distribution.
All the species remaining in "Brachypelma" are found in Mexico. Within Mexico, the largest number of species are found along the Pacific coast. The majority of species are restricted to small endemic ranges in this area.
There is uncertainty over both the distribution of some "Brachypelma" species and their identity. Stuart Longhorn has criticized several arachnologists, including Günter Schmidt, for describing new species based on pet-trade specimens without accurate locations, resulting in vague or inaccurate distributions. He argues that locality information is vital for "scientific rigor", since without it important questions relating to the identity of species cannot be answered. Steven Turner and colleagues have also noted difficulties in identification resulting from the use of imprecisely sourced pet-trade specimens.
Conservation.
Habitat destruction and collection for the pet trade have led to these spiders being among the few arthropods protected under international Convention on International Trade of Endangered Species rules. In 1985, "B. smithi" (then not distinguished from "B. hamorii") was placed on CITES Appendix II, and in 1994, all remaining "Brachypelma" species were added. Large numbers of Mexican tarantulas caught in the wild continue to be smuggled out of Mexico. It is reported that at least 3,000 specimens of Mexican tarantulas were sent to the United States or Europe a few years prior to 2017, most of which were Mexican red knee tarantulas ("B. hamorii" and "B. smithi"). Turner and colleagues suggest that members of "Brachypelma" s.s. (their "red leg" group), which have small ranges and are slow to mature and reproduce, should be the focus of urgent conservation measures, with threats to species in the genus "Tliltocatl" (their "red rump" group) possibly being downgraded.
In captivity.
"Brachypelma" species are docile tarantulas which are easy to keep in a terrarium. The best-known species in this genus are the Mexican red knee tarantulas "B. hamorii" and "B. smithi", as well as "B. boehmi", the Mexican fireleg. They feed on smaller invertebrates and occasionally vertebrates, but while insects are the norm, they may also eat lizards or frogs. These species, like most tarantulas, are cannibalistic, so in captivity, individuals must be kept alone, though brief captive introductions of a mate for breeding purposes can prove unproblematic, so long as they are separated once mating has occurred.
Large spiders used in Hollywood movies (e.g., Indiana Jones series, "The Mummy Returns") are often "Brachypelma hamorii" or "Brachypelma emilia" because they are very docile, though the much less expensive and only moderately more aggressive Chilean rose tarantula is frequently used, as well. While it is almost unheard of for a "Brachypelma" to bite a human, they are quick to kick urticating hairs in self-defense, though their hairs can be less irritating than those of other species, especially the goliath birdeater.
References.
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