Three ways that information can spread in a drone swarm. Direct communication (left) is fast but might saturate the network when many drones send messages simultaneously. Observation (centre) is cheap but often ambiguous: nearby drones’ states and behaviours must be inferred from sensor information. Shared environmental traces or distributed maps (right) enable efficient coordination but require safeguards against unrepresentative or outdated information that could mislead the group. The choice of mechanism depends on the task and on physical conditions.