I most often see bee flies hovering around flowers, or if resting, usually on the ground, on bare soil. They are extremely wary and difficult to approach. No doubt their large compound eyes give them good vision, plus they have that air-motion sensing mechanism that helps the ordinary house fly avoid the swatter. Adult bee flies drink nectar, but the larvae are parasites of beetle larvae as well as the brood of solitary wasps and bees, the hole or burrow-nesting insects. I've heard tales of female bee flies hovering over a hole in the ground, flicking her eggs into the hole. I'm skeptical of these claims. I've often seen female Bombylius sitting in very loose soil, vibrating her butt like mad, so that the dirt is actually thrown outwards (see our Bombylius major pictures). One source says these flies are "gathering sand to coat their eggs", ostensibly to keep them from drying out.