Monster Monday - Spiders

I began to write this last week, but have been sick. I'm trying again this week. Spiders are ubiquitous to dungeon delving. Even outdoor adventures run into the eight-legged monstrosities. They may pop up in cities.
Spiders come in sizes ranging from fingernail-sized, up to (and maybe beyond) the size of a pony. Some are poisonous, and some are merely environmental hazards.
Spiders are essential to megadungeons. They are more important than goblins, trolls, dragons or any other fantastic beast. They lend an air of realism to the dark places. They can tap into dark fears of players.
But, it's what they do inside of the game that makes them shine as monsters.
Want a section of dungeon to look undisturbed for a long period? Cover the hallway in cobwebs.
Want to remove the orcs from an area and replace them with something else?
Leave their web-wrapped, desiccated corpses in corners, and out of the way places.
Need a magical component for Leather Armor? Send the PCs to the lair of Kk'eez, the Spider Demon. His webbing is said to be of great strength, and light weight. He will not give it in an easy bargain, though.
Speaking of Kk'eez, he can be a phenomenal long term villain. His plans spiral out like a spider's web. They touch things that don't seem connected, until the investigators are in the middle. . .

Artwork: © Jack Badashski, 2016 (bought rights on RPGNow)