Lots and lots of ants
I’m sure all of us have walked by a dropped fruit on the ground and have seen a pile of ants warming around it. I have seen this countless times, but never when I happened to have my camera and MP-E 65 on me. Several days ago, I was lucky.
From some research on the Internet, I believe this is Tetramorium caespitum, or the standard pavement ant. They are famous for getting in fights with other colonies, though I do not believe that is what is occurring here.