The genus Sphex is a group of typical Sphecid burrowing wasps. They are distributed worldwide, and are roughly similar in habit. Some groups of species look very similar, and are difficult to identify to species.
They range from around 14 mm to 40 mm body length; the 2 or 3 species more commonly found in Hong Kong generally range from 20mm to 32mm, and there is a very large, all-black species in Singapore, Sphex madasummae (pictured below), which can occasionally reach an impressive 40mm. The shape of this group of wasps is distinct. Many also have attractively marked wings, with dark adorned edges. Generally they have a thin petiole (“waist”), a small oval-shaped abdomen, a rather rounded head with strong, curved mandibles. Their front legs have distinct spines, which serve as digging tools. They are capable of inflicting a painful sting, but never attack of their own accord.
This group of wasps usually prefer to dig in drier, sandy soil, and usually utilize grasshoppers or crickets as prey. They seem to be quite prey-specific, as they usually only target one species of grasshopper or cricket. Usually the burrow is prepared over a long period, and the digging activities are obvious. However, the wasp usually abandons the nest site at the slightest disturbance and starts a new one several feet away. The wasp may also circle or investigate anyone who approaches the nest, but this is never in a hostile manner, and the wasp will soon go back to its digging.