Scientists identify new tarantula species thanks to their giant male genitalia

A new type of tarantula has been discovered and classified by scientists due to their exceptionally large male genitalia.

The spiders – who have been given the genus Satyrex – live in the Arabian Peninsula and the Horn of Africa.

Researchers have identified four different species and the largest, the Satyrex ferox, has a leg-span of about 14cm.

Its palp – a specialised appendage used by male spiders to transfer sperm during mating – can reach an incredible length of 5cm. This is almost four times longer than the front part of the body, and almost as long as it longest legs.

The spiders are highly aggressive and scientists believe their huge genitals may have evolved to help them avoid being eaten by females during mating.

‘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,’ said Dr Alireza Zamani of the University of Turku, who led the study that discovered them.

‘The males of these spiders have the longest palps among all known tarantulas.’

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.’

Ferox, meaning fierce, was chosen for one species as it is so aggressive.

‘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 said.

‘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 said.

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.

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