‘Giant’ tree-dwelling tarantula discovered in Brazil rainforest is a new species
In southeastern Brazil, researchers set out to look for tarantula species with a rare and “striking” characteristic.
Tarantulas, belonging to the Theraphosidae family, are among the largest spiders on earth — a trait that makes an arboreal, or tree-dwelling, lifestyle virtually unheard of among their kind.
But in this section of the Brazilian Atlantic Forest, lurking in the trunks and branches above the team’s heads, was an entire undiscovered group of tarantulas.
Through their fieldwork and examination of museum specimens, researchers identified seven new tarantula species belonging to a new genus called Arboriticus, according to a study published Aug. 15 in the peer-reviewed journal Zootaxa.
Researchers said discovering three of these new species in highly deforested regions of the rainforest is “astonishing.”
“Many specimens were observed on tree trunks and moving between branches during fieldwork,” researchers said. Adults were often found hiding in the cavities of tree trunks up to 8 feet off the ground, the study said.
Among the new rare tarantulas is one very large species researchers named Arboriticus giganteus, after the Greek word for giant, according to the study. Until researchers examined it more recently, it had been an unnamed museum specimen.
The giant species is about 6.4 inches long, with females being larger than males, according to the study. The females were also observed to have thick, powerful back legs covered in stiff hair-like structures.
In addition to their large size, males of the new species are distinguished by their well-developed mating organs, according to the study. 8
Just two Arboriticus giganteus specimens have ever been collected from the Brazilian Atlantic Forest, in the state of Espírito Santo — one in 1981, the other in 2004, according to the study. None were observed in the wild during the recent expedition.
The limited number of specimens observed in the field or present in museum collections is likely evidence of their rarity, researchers said. That goes not just for Arboriticus giganteus, but for all the newly identified species.
“This is concerning, as arboreal species like these are particularly vulnerable to the intense deforestation of their habitats,” researchers said.
For this reason, and because they are found only in these niche habitats, researchers said the species should be considered threatened and “efforts to protect them are strongly recommended.”
The research team included Leandro Malta Bores, Arthur Diesel Abegg, Andressa Paladini and Rogério Bertani.
This story was originally published August 19, 2025 at 11:18 AM with the headline "‘Giant’ tree-dwelling tarantula discovered in Brazil rainforest is a new species."
