Was sind das für kleine Kerle auf meinem Zitronenbaum? (Video)

You’re not going to be calling them “little dudes” much longer. I think those are spider mites and you want to get rid of them asap. They make a fine like weave and will suck the sap out of the leaves until they die. They can reproduce very quickly and be overwhelming. 

I would rinse the leaves, apply a 50/50 mix of water and isopropyl alcohol. Then, apply a miticide or insecticidal soap every 3-5 days. 

If there are other plants nearby, I’d check them and do the same. If they’re not infected, I’d still do the soap once a week.

If you can get your hands on neem oil you are safe