Bembix and a few related genera are rather stout Crabronid wasps, which do not have such an obvious petiole ("waist"). They are powerfully buiilt wasps, ranging from small to quite large, and are usually dark with light steely blue-gray, yellow or whitish stripes and markings. Their eyes are unusually large and somewhat reminiscent of flies (which incidentally are their main prey). The species shown below is one of a few species which can be found in Singapore. I have never taken a close look at specimens and have little information on them, so I have not been able to identify them to species.
They dig burrows in the ground, and are difficult to approach. They are skilled and swift fliers, being able to hover and fly at top speed. When digging their burrows, they are quite nervous and abandon the site if approached; they start a new burrow a distance away. They appear to have very keen eyesight and will react to the slightest movement.
Most species in this group are mainly predatory on flies, although some have been known to take other insects as prey. I have seen the species below catch fleshflies (Sarcophaga sp.). In Singapore, they are found mainly near the sea. Possibly they hunt near rotting shellfish, as Vespa affinis does (read more here).