Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

...Were they intended to be spiders?

They're venomous and emote about clicking their pincers and snapping their mandibles.

Either that or Faerun's Chiroptera aren't as morphologically similar to Earth's as they first appear.

Heh. I came across a char down there that had decided it must be because of the deep mushrooms they eat.

Just imagine them as Predator faced bats!

Image maybe related, if it works:

Spoiler alert. That is the ending of predator vs batman.