What are the movement restrictions caused by natural webs?

Question

In relation to the monster ability web walker, in this case from a giant spider:

Web Walker. The spider ignores movement restrictions caused by webbing.

The only other mentions I can find of webbing is in the web spell:

Each creature that starts its turn in the webs or that enters them during its turn must make a Dexterity saving throw. On a failed save, the creature is restrained as long as it remains in the webs or until it breaks free.

A creature restrained by the webs can use its actions to make a Strength check against your spell save DC. If it succeeds, it is no longer restrained.

Do webs as a terrain feature need to be treated as if it was cast by the spell?

For example, if I want the spiders to have covered the floor with a thin (that is, not the absurd five feet deep as specified in the spell description) layer of web, only enough to obscure any pits etc, could that just be counted as difficult terrain? My intention would be to have the webs as a difficult terrain feature that lightly obscure the walls and floor, but not requiring saving throws to avoid being restrained as per the spell. The spider's web sense ability would still function as normal, and players could easily remove the web with fire and the like.

Answer 1

The rules for webs are detailed in the Dungeon Master's Guide on page 105:

...web-filled areas are difficult terrain... a creature entering a webbed area for the first time on a turn or starting its turn there must succeed on a DC 12 Dexterity saving throw or become restrained by the webs. A restrained creature can use its action to try and escape, doing so with a successful DC 12 Strength (Athletics) or Dexterity (Acrobatics) check.

Each 10-foot cube of giant webs has AC 10, 15 hit points, vulnerability to fire, and immunity to bludgeoning, piercing, and psychic damage.

Since the entire section talks about giant spiders, strictly reading, these rules apply only to webs woven by giant spiders. However, it would be a reasonable ruling to extend these rules since the entire floor is covered by webs of some sort, the entire floor area counts as difficult terrain, yet the PCs need not make any saving throws against being restrained as they are not wholly entering the area affected.

P.S. In my opinion, these rules should be detailed in the Player's Handbook as well.

Answer 2

In short, yes. DC 12 DEX save when starting turn in webs or become restrained. If restrained, make a DC 12 Athletics or Acrobatics check as an action to negate being restrained. Giant Spider says STR check only, no proficiency bonus, so I think it's up to the DM to ask for what check he ​wants.

Answer 3

What is difficult terrain?

According to the PHB, difficult terrain is:

dense forests, deep swamps, rubble-filled ruins, steep mountains, and ice-covered ground

All of these features significantly impede movement - they are not just obscuring the floor. If what you have is a "thin...layer of web, only enough to obscure any pits", that is not difficult terrain. That is simply webbing which produces the lightly obscured condition (thus resulting in disadvantage on Perception checks to spot the pits in the floor).

Only if the webs were thick enough to make every step either laboriously difficult (like steep mountains) or treacherously unstable (like ice-covered ground) would a web-covered floor be considered difficult terrain.

However, even such difficult terrain would not result in forcing saves to keep from being restrained. As you note, the web spell does this, but the minimum height of these webs is five feet, enough to completely engulf most characters. Similarly, the mundane webbing that is treated as a dungeon hazard (DMG 105) provokes similar saves, but only when the webs are "across passages" and create "web-filled areas" that can be defined as a "10-foot cube" of webs. Unless there is some way for webs to completely envelop a character, imposing the Restrained condition does not seem appropriate.