The spider-hunting wasps of the family Pompillidae vary greatly in size. Some are quite small, only 10mm or slightly larger. However, this family includes some of the largest known wasps; these are the Neotropical (tropical American regions) Pepsis species, known as the tarantula hawk wasps. Some species exceed 60mm in length and have wingspans in excess of 10cm! These wasps prey on the giant spiders of the family Theraphosidae, better known to most as the tarantulas.
As previously mentioned, Pompillid wasps generally have long legs and run fast on the ground or on walls, usually in search of spiders. Their nesting habits vary slightly; some species use pre-existing crevices, while some dig simple burrows. They hunt a wide variety of spiders, but each species is fairly specialized in general. For instance, some small species prey on small jumping spiders, only half their body length. However, the above-mentioned tarantula hawks, despite their large size, are dwarfed by their giant prey, yet with their speed and agility, they are able to slip in and deliver a few well-placed stings to the tarantula's unprotected abdomen, effectively paralysing it.
The wasp in the photo above is Leptodialepis bipartitus, one of the larger species in Hong Kong. The photo gives a good idea of how fast these wasps can run; even a fast shutter speed was not enough to overcome the speed of the wasp on foot. They are also swift fliers, and very alert. Therefore, they are quite hard to approach.
The spider-hunting wasps have extremely painful stings in comparison with other species. However, they will never actually attack, and the speed with which they avoid potential danger makes the risk of an accidental sting extremely unlikely.
Follow the links to detailed descriptions and information on various species.