Wurms are large limbless terrestrial reptiles. A wurm has an endoskeleton, reptilian scales or plates, and a saurian head similar to a dragon's.   They may be aligned with any color of Magic, but most are wholly or partially green. Most wurms are forest dwellers. They are preternaturally hungry and relentless when pursuing their prey.
Wurms trace their origin to the Elder Dragon Wars, during which the vastly powerful Elder Dragons that were defeated were stripped of their power, limbs, and wings, thereby becoming the Elder Land Wurms. The Elder Land Wurms are the forbears of all other wurms.
Wurms from different planes can have vastly different morphologies, especially in their head and jaw anatomies.
Upon Alara, the wurms occupy the lower reaches of Jund where they displayed a behavior more akin to dragons than normal. After the Conflux, the wurms were pressed into the service of Bant as living siege engines. 
Elder Land Wurms are creatures of immense power that are the descendents of the original Elder Dragons. During the Elder Dragon Wars, the surviving victors of the war went on the spawn the races of the Lesser Elders, dragons, drakes, and viashino. The losers of the war, the Elder Land Wurms, were stripped of their power and even their limbs, and became the ancient ancestors of modern-day wurms. These beasts might have been stripped of most of their power, but they are still fearsome opponents. A thigh bone of one such creature was found – along with four dead Craw Wurms and a Craw Giant Chieftain – at the site of the supposed last battle of the Ironclaw Orcs.
Craw Wurms are one of the more common types of Wurms. One was summoned by the Kieryn Elves while fighting against the Calthyn Elves in the White Woods of Corondor. Also, corpses of four such wurms were found at the site of the last great battle of the Ironclaw Orcs.
These bizarre creatures looked nothing like any other kind of wurm, having strange, flattened heads and insect-like limbs. They appeared on Terisiare during the Ice Age. One of them killed Zillegeth of Clan Ruby.
Otarian Wurms look a lot like Craw Wurms, except for their flattened mouths. Some of them are known to possess metamorphic abilities. Others have begun a symbiotic relationship with Otaria’s insects.
These wurms have multiple jaws and live in the volcanic rivers under Shiv.
Trench wurms are strange-looking, three-pointed-beak wurms. As these wurms do not look typically Phyrexian, but they were nonetheless deployed in the battle at the Caves of Koilos, it is possible that these were transplanted by Yawgmoth from another plane.
The wurms of Innistrad feast on graveyards, full of bodies ripe for their gullets.
Unlike the generally reptilian wurms of many planes, the Zendikari wurm has a monstrous maw more akin to a Hellion and insectlike eyes. They are worshipped in the creation myths of the Mul-Daya as the parent of the sun.
Wurm creature tokens may come in various sizes, with or without abilities:
- X/X green Wurm (e.g., Baru, Fist of Krosa, Wurmcalling, Wurmweaver Coil )
- 5/5 green Wurm with trample (e.g., Armada Wurm, Worldspine Wurm, Advent of the Wurm)
- 6/6 green Wurm (e.g., Crush of Wurms, Garruk, Primal Hunter, Roar of the Wurm , Wurmweaver Coil)
- 6/6 black Wurm with trample (Penumbra Wurm)
- Doug Beyer. (November 14, 2007.) "Drakes and Dragons, Wurms and Worms", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Doug Beyer. (August 10, 2011.) "Magic's Exclusive Creatures", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (June 08, 2009.) "Sketches: Enlisted Wurm", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Doug Beyer. (December 12, 2007.) "Goodies from the Mailbag", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (October 04, 2005.) "Ravnica Style Guide: Selesnya", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (October 12, 2005.) "Sketches: Autochthon Wurm", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (March 21, 2006.) "Guildpact Token Art 1", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Magic Arcana. (May 30, 2002.) "Bambi Meets Wurm", Daily MTG, magicthegathering.com, Wizards of the Coast.