Spiny backed orb weaver. Species Gasteracantha cancriformis – Spinybacked Orbweaver – BugGuide.Net
They aren’t in the range of Japan. The shape of the spider and range seem to best match Gasteracantha kuhli. https://en.wikipedia.org/wiki/Gasteracantha_kuhli
You are correct. I was shortcutting to avoid digging in reference.
Spiny backed orb weaver.
Species Gasteracantha cancriformis – Spinybacked Orbweaver – BugGuide.Net
They aren’t in the range of Japan. The shape of the spider and range seem to best match Gasteracantha kuhli. https://en.wikipedia.org/wiki/Gasteracantha_kuhli
You are correct. I was shortcutting to avoid digging in reference.