Fearing being killed by sexually aggressive females, male tarantulas evolve extra-long genitals

Scientists have discovered four new species of tarantulas in the Arabian Peninsula and the Horn of Africa. The unique thing about these creatures is their extra-long genitalia located at the front of their mouth. The creatures use this body part, known as palps, to mate with the female tarantulas. Researchers say this is the longest-ever palp ever seen in tarantulas. It is believed that the tarantulas have evolved these enormous genitals to protect themselves from the fierce female tarantulas while mating. The other half of these spiders are known to be pretty aggressive and are even capable of killing the male tarantulas. The study was led by Dr Alireza Zamani of the University of Turku, who said that the new species is so different from its closest relative that they had to "establish an entirely new genus to classify them". The tarantulas have been named Satyrex, after a part-man, part-beast figure in Greek mythology with exceptionally large genitalia. "Rex" in the name means king. The tarantulas might be afraid of the female spiders, but at least their name doesn't give away their secret. The study aptly named “Size matters: a new genus of tarantula with the longest male palps” has been published in the journal ZooKeys.

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How do tarantulas mate?

Male tarantulas do not mate with their female counterparts traditionally and instead use these specialised appendages called palps to transfer the semen. Lengthy palps ensure they are far away from the females, which can even kill them with their aggressive mating behaviour. The largest of the four new tarantula species is the Satyrex ferox, which has a legspan of 5.5 inches, with a palp nearly two inches long. Dr Zamani said that his species is extremely defensive, and "raises its front legs in a threat posture and produces a loud hissing sound by rubbing specialised hairs on the basal segments of the front legs against each other." The study authors have suggested that the long palps are an evolutionary mechanism to help them "keep a safer distance during mating" and “avoid being attacked and devoured by the highly aggressive female.”

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The other tarantulas are S. arabicus and S. somalicus, named based on the region they were found in, and S. speciosus, named after its bright colour. An older species of tarantula, S. longimanus, first discovered in Yemen in 1903, is also part of the new genus.