Crawler
Crawlers are hideous, slithering invertebrate creatures that resemble enormous earthworms or maggots. They are most commonly encountered amid decay and corruption, particularly within the rotting remains of Barrow-wights. Adventurers who fell such undead foes may find that their struggle is not yet over, as a maddened Crawler will sometimes burst forth from the corpse of a vanquished Wight.
Several distinct sub-species of Crawlers are known. These include the Glow-worms, luminescent, serpentine creatures native to the depths of Moria, and the Sand-sifters, a desert-dwelling breed found in the wastes of Shagâna in Haradwaith. Though differing in habitat and appearance, all Crawlers are equally repulsive and share a disturbing affinity for darkness, decay, and confined spaces.
Despite their appearance, Crawlers should not be confused with Worms, a term reserved for a breed of Dragon-kind. The similarity is purely superficial and taxonomically misleading.
Background
Crawlers do not appear in the work of J.R.R. Tolkien. They were created for The Lord of the Rings Online. As with Tolkien's giant spiders, the game assumes that many insects and invertebrates of Middle-earth exist in grotesquely enlarged forms.
A list of all known sightings: