  Ants have evolved to seek and retrieve food by leaving trails of pheromones.
This mechanism has inspired several approaches to decentralized multi-robot
coordination. However, in this paper, we show that pheromone trails are a
fragile mechanism for coordination, and can be sabotaged to starve the colony.
We introduce detractors: malicious agents that leave a misleading, but
indistinguishable, trail of food pheromone to distract and trap cooperator ants
in the nest. We analyze the effectiveness of detractors with respect to
parameters such as evaporation rate of misleading pheromone and fraction of
detractors in the colony. In addition, we propose a countermeasure to this
attack by introducing a new type of pheromone: the cautionary pheromone.
Cooperator ants secrete this type of pheromone atop existing food trails as a
warning. When the cautionary pheromone intensity exceeds the food pheromone
intensity, cooperator ants ignore overlapping food pheromone. We show that,
despite its simplicity, this defense mechanism can limit, but not nullify, the
effect of detractors. Ultimately, our work shows that pheromone-based
coordination, while effective, is also fragile.
