At around 8 am, and just about 70 degrees Fahrenheit, many Centris Bees were actively collecting among the bright yellow flowers that are just beyond their prime by now. But equally many were still asleep, clinging to twigs with their tarsi, but even more firmly with their strong mandibles.
Most insects are ectotherm, meaning that their body temperature depends completely on environmental factors and fluctuates. They can only regulate it somewhat through their behavior. Birds and mammals produce and regulate their body temperature actively through endogenous mechanisms (shivering, panting, sweating, addipose tissue metabolism), which makes them endotherm (this is not to say that they do not use behavioral means of thermoregulation in addition).
But there are exceptions among insects. Big hairy bees and big active sphingid moths, as well as some big beetles and Robber Flies (my own observation) are able to elevate their body temperature using muscle activity that does not translate into movement or at least locomotion, just like their avian and mammalian counterparts who shiver to get warm.
|Birds are highly effective thermoregulators, they can shiver and increase their insulation when it's cold|
|Promachus albifacies buzzing its wings to warm up before it can actually fly|
|Male Centris pallida|
|female Centris pallida|
The sleeping bees do not warm up quickly. While it is usually difficult to get a close look at those constantly hovering Centris Bees, this is an opportunity to study them.
|Male on theft, female on the right|
The faces of the female bees are more fuzzy and grey.
Another difference: his eyes are bigger and more bulging. Male Centris bees are extremely eager suitors, to the point that they try to dig up their late-born sisters to mate with them. Much of that activity is pheromone driven. But often, the males also relentlessly pursue flying females. Those big bulging eyes - to better see her in three-dimensional space?
|Centris bee digging her brood chamber|
|Scopa of the hind leg and setae brush on the front legs of the female|
|Corbicula, a bare concavity into which moist pollen is crammed, on the hind leg of a Honey Bee|
Here is another look at the male Centris pallida - he does not have those brushes of long hairs on the hind tibiae.
Lastly, he also has no ovipositor and that means no stinger. I have handled individuals of both sexes when they were still too cold to fly and none tried to sting me, but I'm too careful to find out whether that is the rule for Centris Bees. They are certainly not as aggressive as social bees and wasps but the females probably can sting.
Literature quoted: The corbiculate bees arose from New World oil-collecting bees: implications for the origin of pollen baskets. Martins AC, Melo GA, Renner SS,Mol Phylogenet Evol. 2014 Nov;80:88-94. doi: 10.1016/j.ympev.2014.07.003. Epub 2014 Jul 15.