leatherback wrote: Hard to tell what is in the soil. However.. Impossible to tell whether they are actually causing damage. Why don;t you start off by giving your new trees proper care, and see whether the tree stays healthy (As, you would not have bought trees that are clearly unhealthy). In general insects are no problem. There are small animals everywhere, and only a fraction of those are really a problem for your plants. These look more link hunting insects than something feeding of your rooots.

Thanks for the tip! I really hope so, I was of course just being extra cautious and wondering if someone has maybe seen something like this. Otherwise the tree looks normal and is doing pretty ok, even though there hasn't really been any new growth since when I brought it home, but hopefully that will sort out itself soon too.

I'm about two years late, but I recently found these I my bonsai pot as well. I'm in a soil science class right now and they are called orbatid mites. They feed on small fungus, algae, dead plant tissue and nematodes and springtails. They're major decomposes and can be found everywhere in nature. If you see these it usually means there's too much water that promotes fungus and algae. My own bonsai was overwatered when I found them. They won't hurt your bonsai.