My mother is 86 years old with dementia and lives with me. She has hallucinations of bugs and is extremely fearful of bugs, lint, dirt, anything that COULD be a bug. I just found a HUGE fake spider in one of my kitchen drawers! It is a drawer I don't use all that often so it could have been there for a week or more. My husband knows nothing about it so it HAD to be someone doing it to scare my mother. But who????? The only people I leave in the house with her unattended is a couple of occasional sitters. The thought that one of my sitters did this to scare my mother makes me sick to my stomach at the very least.
Linolium floor patterns, any small pattern on material.
Now as far as the fake spider, it is cruel beyond words. All i could think of is to say without accusation that you found it, like look what some kid left here how cruel.
Or somehow monitor the place when you are out.