Your screensaver is a folder of 4K video, and it downloads more
Aerial wallpapers and screensavers are full video files stored locally, added to each time you preview one. Where they are and how to remove them.
The aerial wallpapers and screensavers on modern macOS are not images. They are 4K video clips, they are downloaded on demand, and previewing one in System Settings is enough to fetch it. Nothing removes them afterwards.
Where they are
du -sh /Library/Application\ Support/com.apple.idleassetsd 2>/dev/null
du -sh /Library/Application\ Support/com.apple.idleassetsd/Customer 2>/dev/null
ls /Library/Application\ Support/com.apple.idleassetsd/Customer 2>/dev/null | headOn the Mac these measurements come from the folder was empty, because no aerial had been used. That is the honest result and it is the point: this costs nothing until you browse the wallpaper gallery, and then it costs a few hundred megabytes per clip you look at.
Why it grows without you noticing
- Previewing downloads. Scrolling through the gallery in System Settings fetches clips as they are shown.
- Each clip is a video. Several hundred megabytes each, in 4K, and there are dozens.
- Nothing prunes them. The one you set as your wallpaper and the twenty you looked at are treated the same.
Removing them
The files are named by identifier rather than by the name shown in Settings, so removing a specific one by hand is guesswork. The practical options are to remove all of them and let macOS refetch the one you actually use, or to leave them alone.
sudo du -sh /Library/Application\ Support/com.apple.idleassetsd/Customer/*
# then remove individual .mov files you no longer wantSetting a static wallpaper first is worth doing, so macOS is not using the file you are deleting. After that, the gallery will show the aerials as available to download again rather than as missing.
Whether it is worth doing
On a Mac where someone has browsed the gallery, this can be several gigabytes for a feature that shows for a few seconds a day, which makes it one of the better ratios of effort to space on this site. On a Mac that has never touched it, it is zero, and that is worth checking before spending time on it.
If you are working through the system folders generally, what System Data is made of covers the categories this falls into, and Apple's downloadable asset packs are the larger relative on a developer Mac.
Common questions
Where are aerial screensavers stored on a Mac?
In /Library/Application Support/com.apple.idleassetsd, under a Customer folder, as individual video files named by identifier rather than by the name shown in System Settings.
Why do aerial wallpapers use so much space?
Because each one is a 4K video clip of several hundred megabytes, and macOS downloads them as you preview them in the wallpaper gallery. Nothing removes the ones you looked at and did not choose.
Can I delete aerial wallpaper videos?
Yes. Set a static wallpaper first so macOS is not using the file, then remove the video files. They show as available to download again in Settings, so the choice is not lost.
Do aerial screensavers download automatically?
They download when previewed or selected, and macOS also fetches new ones it offers. A Mac where nobody has opened the wallpaper gallery may have none at all, which is worth checking before spending time on it.