Most of the insects are arriving to either collect pollen and/or nectar, find mates, eat parts of the flowers or leafy parts or deposit their eggs so their off-spring can do so. A few spread their eggs so their off-spring can hitch rides on other flower visitors to become a parasitic guest in their nurseries.
And of course this aggregation of spring insects also draws some predators.
|Promachella pilosa female|
|Promachella pilosa male|
On BugGuide Dr. Eric M. Fisher a Diptera specialist with special interest in Asilidae identified
my patio robbers as Promachella pilosa. I am rather proud to say that this added a new Genus and species to Bugguide. Checking the online species data base of the UAIC, I found that there are no (identified) specimens in the collection either.
While it is nice to photograph something new and special (I found no other photos on the web) there is not much information out there either. I have no access right now to Willcox original 1937 paper. So all I know so far is that this is a fly that is only known from Arizona and from neighboring Sonora, Mexico.
But since the appearance is so similar to that of the widespread genus Promachus, and the female is lacking the dagger-like ovipositor of some genera that stick their eggs into plant material, I guess that the females of the genus Promachella deposit their eggs into the soil.