Mud dauber wasps build nests of mud, in a similar way to potter wasps. Their nests are usually long, sealed up, tunnel-like bodies of mud, containing several cells. In each cell, prey will be provided and an individual larva will grow up and pupate into an adult wasp.
Mud daubers are usually slender-bodied, with a very thin petiole (“waist”). There are a number of Sceliphron species found in Asia, and a couple more in Europe and the Americas; these are generally fairly large (14 to 30mm) and mainly black with yellow markings. Another diverse group in Asia and probably elsewhere is a group of probable Chalybion species. These are smaller (15mm average), metallic blue wasps which are common around urban areas. The individual below (from Singapore) is one of the largest I have ever seen, at nearly 30mm.
Mud daubers prey predominantly on spiders; the female paralyses them with her sting, and loads several spiders into each nest cell and lays an egg. When she has stocked the cell with enough spiders, she seals it with another layer of mud, and then immediately starts building another nest cell just next to it. It is not uncommon to find large clusters of such nests in a certain location. Also, if the location is good, it is not unknown for several female mud daubers to start building next to each other, again resulting in a large cluster of nest cells. It is wonderful how each female can recognise her own nest! The photos below show a single nest cell and a cluster.
The photos below were taken in Singapore; in the first, the large mud dauber (Sceliphron sp.) is probably just starting work on its nest. In the second, the mud is still wet, but the tubed shape taking form is already distinct. The other cells have already been completed and have been sealed for some time. First photo copyright and courtesy of Tan Siong-Kiat. Second photo copyright E-Trails Singapore.