I spent a couple of sunny hours photographing lichens in our churchyard using close-up filter and focus stacking. I was surprised to see a purple trail across one finished stack and found it was caused by a minute purple organism that had walked across the frame during exposure. Unfortunately with 1/15 second exposure it isn't totally sharp. I later identifed this as Vertagopus arboreus about 2mm long and a member of the Collembola, or Springtails, one of the largest groups of insect-like organisms found in the soil. A close relative of silverfish, these arthropods include over 6000 separate species world-wide. They are no longer considered insects but remain arthropods for classification purposes.