Cacoxenus indagator (garden)

“Cocoxenus indagator, a ‘fruit fly’ that starves some solitary bees to death

You may see these little ‘fruit flies’ around your red mason bee nest boxes. This feeble flying insect is no fruit fly as a larva. It is a cleptoparasite . They are opportunists and literally hang around watching and waiting. They are looking to sneak into an empty cell, check it out to see if any pollen has been stored. If it has, she will quickly lay some eggs and leave pretty pronto before the host bee returns. The resulting larvae eat the pollen store and in many cases if there are simply too many of them, the bee larva will starve, usually to death. You can find up to ten larvae in one cell.”

Interesting to find it in a Blue mason bee nest