Centris pallida is an exceptional looking bee, somewhat fuzzy and grey in color. It is found in the US Southwest, which is mostly a desert environment. Therefore, it is often referred to as a desert bee, or a digger bee, and sometimes even the pallid bee, due to its habitat, actions, and color. Strangely enough, for a bee that is as striking to look at as this bee is, it lacks an accepted common name.
The adult bee emerges in April or May and only lives for about one month on the surface. By late July it is hard to find any Centris pallida as they have mated, provisioned the new generation, and died.
This solitary native bee is found in dry landscapes. The more arid the better. It is a member of the Apidae family, and some people think it is a strange looking honeybee. But the honey bee is Apis mellifera, a different type of bee.
Over 110 species in the genus Centris are scattered from the US state of Kansas in the north down to Argentina. The densest representation of this species is found in Central and South America, as well as on the island of Jamaica.
This bee is black, with grey fur on the dorsal side. The ventral side is covered in brown or dark yellow fur. Their wings are quite transparent with black veins. Their eyes are prominent and male eyes are more yellow while female eyes are greener.
This 6:44-minute video by Cintia Borda gives great visuals of Centris pallida:
These bees particularly enjoy foraging on orchids and flowering trees. In the US Southwest, Centris pallida is very fond of foraging on the glorious yellow blooms of the Palo Verde (Parkinsonia microphylla) trees, the state tree of Arizona. These unique trees, named ‘green stick’ in Spanish, experience photosynthesis through their green stems. C. pallida also pollinates desert willows, ironwood, creosote bush, and cacti.
Centris pallida has evolved to withstand higher temperatures than most other bees. It is not uncommon for them to have internal temperatures that are within 3 degrees Celsius of death. Males are often 48 to 49 degrees Celsius (118.4 to 120.2 degrees Fahrenheit). If their temperature reaches 51 to 52 degrees Celsius (123.8 to 125.6 degrees Fahrenheit), they get paralyzed and die. They hide in shade during the daytime, so they do not overheat, and are active at night. Their fur and exoskeleton allow them to survive cold nights in the desert.
This solitary desert bee is perhaps best known for its mating behavior and strategy. Once a female decides she is going to emerge, she releases pheromones that attract the attention of males on the surface. Males have two patterns—hovering and patrolling. The first one is that males ‘hang around’ good food sources. When females arrive to forage, the males attack them. The second method is that the males wait near the buried nests and dig up the females as they emerge. Sometimes the males dig up the wrong species, like honeybees and other insects by mistake. They are in such a rush to mate that they dig before knowing if the emerging bee is male or female. Once they establish it is female, they start mating right way in the hole they dug. Imagine this scenario—there can be thousands of males waiting for females to arrive at food sources or outside their burrows waiting for them to emerge.
One scientific paper indicates that female bees can determine the mating strategies of their offspring by how they construct and provision their nests. Size plays a role, and female bees have their say in this system. Smaller males hover near food sources, while larger males dig up the virgin females. The size of the bee depends on how much food the bee had during its developing larvae stage.
Female bees can influence the behavior of their sons by the way they provision and build their nests. For smaller male sons, the female bee will make and provision many small cells in their burrow, whereas if she wants bigger male sons, she will make fewer cells and they will be larger and hold more rations. Although females provide ‘bee bread’ like other species, theirs differs in that it has the consistency of molasses instead of being solid and it is often orange due to the color of Palo verde nectar and pollen.
The greatest threats to these bees are desert birds and lizards which feed on them, as well as rain which can flood their burrows and cause them to drown.
Centris pallida is an excellent solitary bee species to study if a variety of bee mating patterns interests you.