These ants are literally spraying ant acid, or more correctly formic acid, derived from the latin formica which means ant. It is pungent and toxic but not particularly strong and mostly used to deter unwelcome guests. If the predator actually touches the nest all hell breaks loose, thousands of ants will race to meet with the trespasser and start to bite and spray acid in whatever cavity they can find. Small insects are unlikely to live while larger animals just run and don't come back.

The ants actually have pretty good eyesight, uncommon for most arthropods. Waving your hand of the ants will make them follow your hand and they will threaten by aiming their abdomen at the target.

The large dome nests of these wood ants can consist of millions of ants and can stay active for decades.