Colony Density and Activity times of the Ant Camponotus semitestaceus (Hymenoptera: Formicidae) in a Shrub Steppe Community1

Colony densities and above-ground activity periods were determined for Camponotus semitestaceus colonies within a shrub-steppe community. Colony densities ($$\bar x$$ ± SD) averaged 0.088 ± 0.032 per m² and 0.048 ± 0.028 per m² on two sagebrush-bunchgrass sites and 0.028 ± 0.028 per m² on a burned site. Seventy-five percent of the nest entrances were located alongside the stems of sagebrush, indicating a preference for these microhabitats as nest locations. Above-ground activity times were determined by using time lapse photography. Activity commenced shortly after sunset, when light intensities dropped to 2.5 to 1.0 foot-candles (ca. 27 to 11 lux) and terminated just before sunrise. Light intensity appears to be the primary cue for controlling above-ground activity periods of this species, but temperature also appears to be an important factor. When soil surface temperatures drop to 1.7 to 3.9°C, all above-ground activity ceases, irrespective of light intensity.