Thank you all for your feedback and links. Much appreciated.
Looks like I am hooked on this subject now. Has anyone seen this post:
https://forum.inaturalist.org/t/why-was-this-xylocopa-bee-so-fixated-on-one-place/24263/5
In a hot climate it makes sense (to me) to be keeping still and rest during the hot hours of the day. I keep seeing flies (that would normally be taking off very fast) resting (sleeping?) very prominenty on an exposed leaf in the shade, letting me move around them taking pictures. I guess it’s safe to assume that they, too, prefer to conserve energy (and humidity) when it’s so hot.