If you asked me 10 years ago if cleaning spider poop would ever be something I would spend a day researching, I could pretty much guarantee the answer would be no.
But here I am, having researched and tested out some spider poop cleaning options. The first thing I tried was some basic soap and water, which really did nothing to cut away at the stains on my siding. Research showed that this was a big problem for boaters in Florida, where spiders would create webs under their boat covers, then drop excrement onto the white boat deck causing black stains. This has lead to commercial products such as Drop Off Cleaner. That website is actually pretty funny to visit.
At any rate, as it turns out tire cleaner does an amazing job instantly removing spider droppings from white siding. I’m not sure what it would do to other colours of siding, I suspect it would change the colour of the siding. First world problems.