Worm

Worms are enemies in, , , and , normally encountered by killing a Butcher/Bloater. In SAS 4, they are mentioned as "secondary larval parasites" in the Bloater description, meaning the worms live inside Bloaters, using them as hosts.

While worms do not appear in SAS 2, they do appear in the expansion, Insane Asylum. They return in SAS 3, this time yellow in color. In the mobile port, one Daily Mission specifically focuses on them, with the player having to fight waves consisting solely of the worms, which can be done easily through use of pistols.

"For stronger enemies spawned by Regurgitators, see Puke Worm."

In, they look much different, this time like green slugs. Generally found by killing a Bloater, they can also be encountered living freely through Events, Vaccine, Survivors, Zombie Pods, Meltdown, and Last Stand without spawning from Bloaters. Just like any other zombie, they have Regular, Fetid, Evolved, and Apex versions, according to their host (Fetid Worms from Fetid Bloaters, Evolved Worms from Evolved Bloaters, and so on). Until the October 9th update, they did not have any buffs other than health and damage, and it'll now have the buff the Bloater had, unless encountered living freely, where it will not have any buffs.

Trivia

 * Worms will not spawn any virus vials in Virus Samples, possibly because they are secondary enemies, just like Puke Worms.
 * In the mobile version, Worms are peach instead of green.