ABSTRACT.1. Patterns of daily and seasonal activity for seven species of tenebrionid beetles, genusEleodes, were investigated in the shortgrass prairie of northeastern Colorado. The relationship between time of activity, body temperatures, and rates of water loss of the beetles was examined in the field and in laboratory experiments.2. Common species were active from April until the end of October; however, asynchronous peaks of abundance occurred.3. Beetles were diurnally active with peaks of daily activity occurring 2–4 h after sunrise and before sunset. Less than a 2 h shift in mean time of activity occurred between seasons.4. Within species, body temperatures measured in the field closely corresponded to temperatures selected in an experimental thermal gradient; hence, species seemed to prefer particular body temperatures and were most active during times when those temperatures could be achieved. Body temperatures measured in the field approximated ambient temperatures measured in the vicinity of the beetle.5. Significant differences among several species were found for times of daily activity and corresponding body temperatures.6. Ability to resist water loss by evaporation was not correlated with daily or seasonal activity pattern