I brought my mandevilla inside to winter over, but yesterday when I was moving it discovered a large amount of these fine black excretions in the pot saucer...they seem too regular to be dirt and have a sort of "gummy" feel to the touch



anyone know what it is? Couldn't find any bugs on the plant but I moved it out to be sure there wasn't something hiding and infecting other plants.

Could be millipedes. You generally won't see them come out, but you'll find their poop every time you move the pot (as me how I know ). The poop is gross, but they're harmless at least.