Between, behind the amazing compound eyes are three additional eyes. What must it be like, to see in such different ways? Why have those three extra eyes, in addition to the huge compound eyes? My guess: rapid response, for predator evasion. The simple eyes point in the direction a predator is likely to come from. They can be hardwired to the brain, not requiring complex processing before the beefly can take instinctive evasive action. (Even though I moved fairly close, I moved slowly, and the beefly seemed to remain relaxed, cleaning itself off.)