In the picture below, the two larger black ants are Black Valentine Ant (Crematogaster laeviceps). When I saw this ant in the field, I thought it was the Asian Army Ant (Pheidologeton diversus) as it was too small to differentiate the two. Also, the size and pattern of the marching column looked similar to the Asian Army Ant. The only thing that puzzle me was that the ant was not as aggressive which it supposed to be as Asian Army Ant. When I examined the picture back home with a larger view, it turned out to be another ant species --- no wonder it was not aggressive.
It may look similar to the Cocoa Black Ant (Dolichoderus thoracicus). However, the Cocao Black Ant is larger in size and only slightly smaller than the Black Valentine Ant.