The 36-year-old actor encountered the spider type for the first time while filming an episode of his nature documentary series Wild Things in Laos, reported Digital Spy.
German spider expert Peter Jager has named the creature Ctenus monaghani in honour of Monaghan thanks to his enthusiasm upon discovering the spider.
"He places nature in the foreground in a very special manner," Jager said.
On Wild Things, Monaghan explores dangerous locales and encounters equally dangerous wildlife, including exotic and deadly snakes.
The Ctenus spider can be between 1-3cms in length, and are a nocturnal species who roam along jungle floor for prey.