Snakes were a group of reptiles which lacked limbs. Snakes were sometimes referred to informally as serpents. Some snakes were venomous.
On Earth, there was an ancient African myth about a giant serpent called the night beast. (ST: "The Girl Who Made the Stars")
The 22nd century Earth Starfleet survival training course involved living on recycled sweat and snake meat. (ENT: "Desert Crossing")
In the mid-22nd century, Hoshi Sato and two other teachers from Amazon University took a hydro-skimmer to visit a tributary of the Amazon River. Sato saw sloths, pink dolphins, and many kinds of snakes there, which frightened her a lot. (ENT: "Fight or Flight")
A snake that would fall down on a hapless victim when a doorbell was pulled was part of the Sherlock Holmes holographic story that Data and Geordi La Forge ran in 2365. (TNG: "Elementary, Dear Data")
When Commander Riker was suffering from acute lack of REM sleep in 2367, he hallucinated that there were snakes underneath his blanket. (TNG: "Night Terrors")
In 2370, the D'Arsay archive turned parts of a photon torpedo on USS Enterprise-D into living snakes. (TNG: "Masks")
The group of snakes included garter snakes, rat snakes, and milk snakes, all common and harmless.
A green and white striped snake was native to the planet Bajor. Vedek Bareil saw one of these snakes during an Orb experience in 2370. (DS9: "The Collaborator")
The snake in Bareil's vision was an emerald tree boa (Corallus caninus).
A yellow snake species was also native to the planet Soukara. Jadzia Dax and Worf encountered one of them during their mission on Soukara. (DS9: "Change of Heart")
The snake on Soukara was an albino Burmese python (Python molurus bivittatus), a color variant popular in the pet trade.
Trakor's Third Prophecy made reference to vipers, indicating the existence of snakes on Bajor. (DS9: "Destiny")
Types of snakes and serpents
A creature that appears on Dakala in ENT: "Rogue Planet" was referred to, in that episode's final draft script, as a snake, but is referred to as a "bug" on screen.
Sentient snake-like species