Interesting symbiotic relationships

Symbiosis – living together
We all know what Symbiosis means. It has many different forms, but the main ones are: Mutualism, Commensalism and Parasitism (although there are some discussions among scientists concerning the last two forms).
Anyway, I am not going to argue with them and shall include in this list photos depicting any kind of long-term interaction between two or more species.
Sometimes the symbiosis is not so obvious and I would miss some examples. Please help me to create this list together adding respective remarks to the description of photos you upload.
No doubt, it will be of mutual benefit. (Wow, Mutualism!!!)