The red "backpack" on the second ant is a mite that lives only on the bodie of army ants. Mindo, Pichincha, Ecuador.
Liometopum occidentale velvety tree ant workers tending larvae of the copper butterfly Lycaena xanthoides. The caterpillars produce a substance attractive to the ants, and the ants provide protection from predators and parasites. Kern County, California, USA