Nest: workers of different sizes and colouration (differing degrees of orange and black)
Strobe ant. There turned out to be many on this tree; since a group of weaver ants was also on this tree, I am guessing that some mimicry is involved.
Here is a video of it exhibiting very jittery movements: https://www.youtube.com/watch?v=z63wH0H_FBc&feature=youtu.be
Another such ant on the same tree was https://www.inaturalist.org/observations/2757897