Four new species of tarantulas have been discovered in the Arabian Peninsula and the Horn of Africa. But these aren’t just any tarantulas.

“Based on both morphological and molecular data, they are so distinct from their closest relatives that we had to establish an entirely new genus to classify them, and we named it Satyrex,” explains Dr. Alireza Zamani of the University of Turku, who led the study that discovered them.

The genus name is a combination of Satyr, a part-man, part-beast figure from Greek mythology with exceptionally large genitalia, and the Latin word rēx, meaning “king.”

But why “king,” and why a Satyr? “The males of these spiders have the longest palps among all known tarantulas,” Dr. Zamani says. Palps are the specialized appendages used by male spiders to transfer sperm during mating. In Satyrex ferox, the largest species in the genus with a legspan of about 14 cm, the male palp can reach an incredible length of 5 cm, which is almost four times longer than the front part of the body, and almost as long as it longest legs.

The name ferox means “fierce”, and it fits. “This species is highly defensive. At the slightest disturbance, it raises its front legs in a threat posture and produces a loud hissing sound by rubbing specialized hairs on the basal segments of the front legs against each other,” Dr. Zamani explains.

“We have tentatively suggested that the long palps might allow the male to keep a safer distance during mating and help him avoid being attacked and devoured by the highly aggressive female.”

As for the others in the group — the researchers named S. arabicus and S. somalicus after their respective regions of origin, while S. speciosus gets its name from its bright and beautiful coloration. The genus also includes an older species, S. longimanus, originally described from Yemen in 1903 and previously placed in a different genus.

“Satyrex longimanus, despite also having an elongated palp, was formerly classified in the genus Monocentropus, where the male palp is only about 1.6 times the length of the carapace and well within the typical range of 1.5 to 2 times seen in tarantulas. The much longer palps of S. longimanus and the four newly described species were among the primary characters that led us to establish a new genus for these spiders, rather than place them in Monocentropus. So yes, at least in tarantula taxonomy, it seems that size really does matter,” Dr. Zamani says in conclusion.

All members of this genus are fossorial, meaning they live underground, in burrows at the base of shrubs or between rocks.

The study was published in the open-access journal ZooKeys.

Research article:

Zamani A, von Wirth V, Fabiánek P, Höfling J, Just P, Korba J, Petzold A, Stockmann M, Elmi HSA, Vences M, Opatova V (2025) Size matters: a new genus of tarantula with the longest male palps, and an integrative revision of Monocentropus Pocock, 1897 (Araneae, Theraphosidae, Eumenophorinae). ZooKeys 1247: 89-126. https://doi.org/10.3897/zookeys.1247.162886