Much of that coordination happens through chemical signals.
Ants communicate using pheromones and other chemical cues. These signals can help workers locate food, recognize members of their colony, follow trails, respond to danger, and coordinate defensive behavior.
When the nest is damaged, the chemical environment can change dramatically.
Workers may detect alarm-related signals and begin responding.
Depending on the species, some workers may rush toward the damaged area while others move deeper into the nest.
Some may attempt to carry larvae or pupae to safer locations.
Others may begin repairing tunnels.
This response can happen surprisingly quickly.
To a person standing above the nest, it may look as though the ground has suddenly “come alive.”
But from the colony's perspective, something much more important has happened.
Its protected environment has been breached.
The nest provides shelter from weather, predators, parasites, and environmental changes. Some ant colonies construct elaborate underground chambers with different areas used for brood, food storage, and movement.
Destroying even part of that structure can create a serious problem for the colony.
This is why ants may respond strongly when someone steps directly onto or digs into a nest.
The insects aren't necessarily interested in chasing humans across a forest.
They are responding to a local threat.
However, the defensive behavior of ants varies enormously between species.
Some species primarily bite.
Others can sting.
Some can both bite and sting.