Daily Nest Opening and Closing of the Ant Pogonomyrmex Californicus

In a study of timing in this ant ten of the twelve nests which were observed opened synchronously in the morning and closed in the evening. However, one was never seen to close and another closed during the day and stayed open at night.A seasonal progression was shown by later opening times and earlier closing times. Opening and closing temperatures at the surface of the ground and three inches deep showed no seasonal progression.In most cases the days when the nests opened the earliest the temperatures at opening time were the highest.Soon after nests had closed they were illuminated but remained closed until the usual opening time. When nests were cooled with ice their opening time was delayed significantly.Possibly opening and closing are clock controlled, occurring if a suitable temperature is reached within certain timed segments of the day; such a clock might be kept in phase by the whole light (or temperature) cycle.