In Star Trek, the Arachnid Nebula is an interstellar dust cloud located far from the planet Vulcan. The Arachnid Nebula was featured on the front cover of "The Cosmos A to Z", an astronomy book by Laura Danly that claimed the nebula was 6.5 billion kilometers in diameter. The book which was an inspiration to Captain Jonathan Archer in his childhood. In 2151, the NX class starship Enterprise and a Vulcan civilian transport vessel, the Vahklas, completed a survey of the nebula. The crew of the vessels found that it was actually more than 8 billion kilometers in diameter, not 6.5 billion. They also noted over 20 million cubic meters of disodium and traces of ethylchlorate in the nebula. Enterprise intended to send back the new information to help revise the astronomy books. (ENT: "Fusion")

In astronomy, there is no actual nebula called the Arachnid nebula. However, the image used to display the Arachnid nebula in Star Trek bears a striking resemblance to the Tarantula nebula (aside from the blue colour used in the Star Trek image). The Tarantula Nebula (also known as 30 Doradus, or NGC 2070) is an H II region in the Large Magellanic Cloud. The Tarantula Nebula has an apparent magnitude of 8. Considering its distance of about 180,000 light years, this is an extremely luminous object. Its luminosity is so bright that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies. It is also the largest and most active such region in the Local Group with an estimated diameter of 200 parsecs. The closest supernova since the invention of the telescope, Supernova 1987A, occurred in the outskirts of the Tarantula Nebula.

The tarantula is, of course, classified in biology as an Arachnid.