solitary populations, nesting begins later and only one brood is produced. The brood has a sex ratio made up of 60% males, similar to that of the final brood in social populations. This brood is also produced at about the same time that the final brood is produced in social populations so that the colony cycle ends at about the same time regardless of where the population lives. Body size Temperature affects not only the sex ratio, but also the size of offspring in the first brood of Halictus rubicundus, with warmer temperatures strongly correlated with larger offspring; there are various hypotheses that offer explanations as to why such is the case: At optimum temperatures, the maximum offspring size will be produced. Smaller sizes will be the result of both higher and lower temperatures based on differing stresses. So varying conditions around one optimum temperature will lead to different offspring sizes. This hypothesis is not supported by existing data. Low temperatures may reduce flowering, or reduce bees' ability to forage during the day, and therefore effect the rate of cell provisioning. If the rate of provisioning is lower, females may lay eggs on pollen masses before the mass reaches an optimal size. This hypothesis is supported by existing data. An offspring's size is not correlated with the size of their mother; foundress females that are smaller than the population average produce offspring that are larger than they are, and foundress females that are above the population average produce offspring that are smaller than they are. Once a nest contains workers, the size of offspring ceases to correlate with temperature, and instead correlates very strongly with the number of workers foraging for pollen, with the largest offspring (both males and females) being produced in nests with the greatest numbers of foragers. Behavior Halictus rubicundus is widely studied for their variability in behavior depending on geographic location, and with changes in temperature. Those at low elevations are known to exhibit eusocial behavior, while those at high elevations and latitudes are known to be solitary. Dominance hierarchy There is a caste system in H. rubicundus. The nest-founding females recruit their early-emerging daughters as workers, but later-emerging offspring mate prior to dispersal and hibernation. These behavioral categories are not thought to be genetically predetermined, but determined instead by mating behaviors and social factors in the first few days of adulthood. In this hierarchy, there