Larger females are able to better control the size of their offspring. As stated in the Life Cycle section, more bee bread leads to larger offspring. Larger females are able to gather more pollen and nectar in a shorter amount of time when compared to smaller females. This means that during rich conditions, the larger females can have larger offspring with greater fitness, or if conditions are poor, the females can simply choose to have smaller offspring. There is a lower limit to how small offspring can be, and thus, smaller females can’t make this reduction or increase in size in response to the environment. Smaller females are still able to exist since larger females can’t take advantage of having larger offspring when the density of nesting grounds is low. To put it another way, larger male offspring are less effective in low density nesting grounds since they don’t have as many opportunities to use their size to fight off other males; thus, in low density nesting grounds, small and large males have similar fitness which means that the extra bee bread which the larger male received served no purpose. Smaller males actually do better in low density areas because they don’t have to fight with larger males as much, and by extension, expend less energy. This lack of a reason to produce larger offspring reduces the fitness of the larger females since they have to dig larger tunnels to fit in, but still produce the same size offspring as smaller females.
Centris pallida are able to withstand very high internal temperatures when compared to other bees. Males regularly have thoracic temperatures of 48 to 49 degrees Celsius (118.4 to 120.2 degrees Fahrenheit). If the thoracic temperature reaches 51 to 52 degrees Celsius (123.8 to 125.6 degrees Fahrenheit), the bee will become paralyzed and die. Most of the cooling occurs when heat radiates off the abdomen. To prevent overheating, C. pallida have a very high thoracic conductance (rate of heat transfer from the thorax to the abdomen) which is 45 percent higher than that of sphinx moths of the same size. Other than this high thoracic conductance, no other mechanism has been found to help the bee reduce its internal temperature. C. pallida do not appear to have evaporative cooling in the wild as honey bees and bumblebees do.
Centris pallida are located in dry, hot environments of North America. Specifically, they are in Arizona, Nevada, southern California, New Mexico, and western Mexico. They are a very common bee (especially in Arizona), and are thus classified as Least Concern in terms of conservation. The fur and dark colored exoskeleton allow the bees to survive the cold nights in the desert. During the daytime, C. pallida are almost completely inactive, hiding in shade or in burrows to prevent overheating.
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