I'm honestly curious about this, why do people get scared of in game models of spiders?
Aracnophobia, perhaps on an irrational level for some people. Nonetheless, I feel for the people who are fearful of spiders. At least this game doesn't have clowns in it. The masks in Orlais though? Creepy.
So in the Storm Coast, there's a few caves where they spawn. Scratch the few, they spawn in every cave except for Daerwin's Mouth which is northwest of the western most camp, also known as Driftwood Margin Camp.
They also spawn in places at the Emerald Graves, where exactly I cannot recall, but I do know a big one spawns there. I think it's quest related, because I can't find it after having run around most of the map.
Another location where spiders spawn is in the Hissing Wastes, located at the bottom of the Canyon near where the merchant is. I believe you have to have access to the Western Approach and complete a War Table operation to unlock the zone... found another lot of spiders in the tomb to the far north, where the Colossus is. Being an area in perpetual night, I think most of the tombs will house spiders.
I recall some spawning in the Hinterlands once you move the Druffalo from near that level 12 Fade Rift. Uhm... they also spawn in another area but I can't for the life of me recall where. You know what? I'll jump in game and find the areas I know of, will update as I scour each zone. Will continue this at a later date, the save I'm doing this on is almost complete, however the second game I'm playing through is only just begun so I can list them as I find them.
I haven't run into any that drop from the ceiling, or if I have, I don't recall it. Now the next part is spoilery, so I will put it into spoiler tags.