I put a toothpick in the soil to gauge how wet it was, and when I pulled it out, there were several very small bugs crawling on the toothpick. They are black and about 1.5 mm long. They are long like a worm and not round. They crawl about quite quickly. I won't post a picture because they are probably too small to see. I haven't put a toothpick in before, so I don't know how long these pests have been in there and if my bonsai is in danger from them. I also don't know where they would have come from. I keep the tree inside. The tree seems quite healthy, so I don't know if I need to be worried or not.