There could be plenty right nearby, or right here. We don't even know what is on the sea floor, or not even very deep underground. If trees are thinking, we do not know it. Something that lives a thousand times our speed would be invisible.
If they don't interact with E-M fields, we could walk right through them, or they us. Our ground wouldn't hold them up against gravity, but they could have ground of their own, with a surface a thousand miles up, or down.