I’ve occasionally seen very small spiders, some with webs and some just scooting around, between closed window panes where there should not be any food available. Also seen between screens and closed windows. What the hell are they living on?
Obviously those environments that you think are sealed aren’t.
They may be young spiderlings that got into the space but will eventually die of starvation or leave. But there may be even smaller insects or arthropods living in the spaces and eating mold, bacteria, or algae, like mites or book lice, that provide them with food. These may be so small that you don’t notice them.
little spiders are so cool. small moving dots.
a spider may lay eggs in the cracks between the window and frame. when these hundreds of eggs hatch then the little buggers go in all directions.
many things like insects produce hundreds of off spring to have a few survive.
The modern-day equivalent of toads inside rocks, I guess.