This was probably the inspiration for a lot of similar programs on Mac/Windows/X11 in the early 1990s in which various things happened to the desktop -- creatures devouring the desktop, creatures just wandering around it, snow accumulating on the tops of windows, etc.

Still available!

https://apps.microsoft.com/store/detail/esheep-64bit/9MX2V0T...

The old version of this inspired me long ago to try to do a malicious version of it. It used a picture of Pikachu, who'd sometimes melt windows in DOOM screen transition style and force them to close. I think I had a working prototype.

The line about the optical illusion of the legs moving due to the background colour reminds me of this recent HN post: https://news.ycombinator.com/item?id=34553705

This is a classic. "Killer crabs start eating their authors" always brings a smile to my face when I remember it.

That's terrifying. More!