Specific to "Polyergus", when the queen first enters a "Formica" nest she releases a pheromone from her enlarged Dufour’s gland. Topoff did experiments to show that this pheromone has an important facilitative effect in colony usurpation; it reduces the aggression of the defending "Formica" workers. The researchers took the Dufour’s, pygidial, and poison glands from freshly mated "Polyergus" queens, using water as a negative control. These were crushed in distilled water to make a solution containing their extracts. Because it was impossible to prevent a "Polyergus" queen from secreting her own pheromones during a live encounter, they used the harvester ant "Pogonomyrmex occidentalis" (naturally attacked by "Formica") as the subject. These ants were dipped in the above solutions, one ant/solution/test at a time, and placed in a petri dish with three "Formica occulta" "attackers". They were observed for three minutes to see for how long the "Pogonomyrmex" was attacked. The results were as follows: "the mean duration of aggression by the Dufour’s gland treatment was 53.3 seconds...The mean duration of aggression for the water, pygidial gland, and poison gland controls were: 143.5 seconds, and 137.2 seconds and 132.2 seconds respectively". Apparently, at some time, "Polyergus" queens evolved the capacity to passively facilitate colony takeovers.