Today, while looking at a fern sporangium at 100X magnification through a microscope, where the sporangium looked like a miniature forest, my son Liam and I were surprised to see first one and then another tiny white spider come walking out of the miniature forest.
They were very busy moving about and had spun a very fine thread of web between two bits of the sporangium. We estimate their size to be no bigger than 0.1 mm in diameter, invisible to the naked eye, but clearly a plump, waxy white spider with medium length legs as seen through the microscope.
Thanks for this. We went and looked at pictures of spider mites, which we didn't know could also spin webs, and these are certainly the right size. We couldn't find any that looked quite like the ones we saw, which are very typically spider-shaped, but I guess that is a question of identifying the specific species.