Tarantula Species With Penis That Dwarfs Its Body Discovered By Stunned Scientists
Researchers suspect these exaggerated organs evolved as a survival tactic, keeping males at a safer distance from their cannibalistic mates.

Zamani et al. 2025
Scientists have stumbled upon four new species of tarantulas whose males have such outrageously long genitals that they had to invent an entirely new genus to classify them: Satyrex, named after the mythological satyr—half-man, half-goat, all libido—and the Latin word for king, rex. The males of the newfound species boast palps (spider sperm-delivery appendages) that stretch up to four times the length of their upper bodies and rival their legs in size. Most species top out with palps twice the length of their head and thorax combined. But in Satyrex ferox, the largest and fiercest of the bunch, the male’s palps clock in at a full 2 inches—nearly half its leg span. Researchers believe these exaggerated organs evolved as a survival tactic, keeping males at a safer distance from their famously cannibalistic mates. Satyrex arabicus was found in Saudi Arabia, Satyrex ferox in Yemen and Oman, and Satyrex somalicus and Satyrex speciosus in Somaliland. The spiders live in rocky crevices. “At least in tarantula taxonomy, it seems that size really does matter,” said Alireza Zamani, the study’s lead author and an arachnologist at the University of Turku in Finland.

The palps shown in images C to F are from the newly identified tarantula species—while A and B are from previously known tarantula species for comparison. The small black lines are scale bars representing two millimeters.
Zamani et al. 2025
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