This is a fairly large hornet, ranging from 23mm to 35mm in length. The size difference between queens and workers in this species is not very great. It is a fairly slender species with a fully yellow head. The thorax is mainly black; the pronotum (two sides at the front) may be yellow-brown or black. The first two abdominal segments carry a large area of brown, yellow and black striping, while the rest of the abdomen is black. There may or may not be a yellow stripe on the margin between the third and fourth sections.
This species is found in Hong Kong and much of China, Taiwan, Korea, Japan and even Siberia. In Hong Kong, it is the least common species but can be found in quite a wide range of habitats, including urban areas in less congested or polluted regions. It does not generally fly near people, and is fairly secretive and timid; it does not always flies in the open.
This species is also similar in appearance to Vespa soror; in fact, I considered all such wasps in Hong Kong to be Vespa ducalis until I noticed substantial differences in structure and behaviour and then sent specimens for expert verification. Vespa ducalis is smaller and more slender than Vespa soror; it has a normal sized head (not greatly widened behind the eyes), and the stripes of various colours on the abdomen are darker and far more contrasting than those on Vespa soror (shown below). It is important to be able to differentiate the two species in the field, for both species differ greatly in temperament and it would be risky to mistake a nest of Vespa soror for that of the gentle Vespa ducalis!
This species was formerly considered a subspecies of Vespa tropica. Several recent papers have been written on these two species, confirming Vespa ducalis as a valid separate species. Structural characteristics aside, it is totally different from Vespa tropica in appearance and behaviour. The two species also have very little geographical overlap, and in fact, Hong Kong is one of the few places in which both occur together. It should be noted that past research on Vespa tropica (sometimes listed as subspecies "Vespa tropica pulchra") in Japan actually concerns Vespa ducalis.
This species specializes in attacking the nests of Polistines (paper wasps) and capturing the larvae to feed their own larvae. It is said to be almost exclusive in choice of prey, and very rarely takes other prey. It is said that a colony of Vespa ducalis needs at least 120 to 150 colonies of Polistine wasps to survive! Vespa ducalis, like its near relative Vespa tropica, usually hunts singly among trees and shrubs in search of such wasp nests. When it locates one, it will land on the nest, immediately proceeding to pull out larvae and pupae, often tearing the cells in the process. The original occupants usually hide in a corner or flee the nest, never fighting back! Like Vespa tropica, and unlike Vespa soror, this species seldom kills the original occupants, being content to drive them to one side so it can capture the larvae without resistance.
The nest of Vespa ducalis is usually underground or in a crevice. Due to the location, the nest is seldom seen. If excavated, the nest looks like an overturned bowl, with an open bottom (as opposed to the completely sealed nests of most aerial hornets). The nest envelope is laminar (comprising of distinct, broad individual layers) and very brittle. This species supposedly has the smallest colony sizes of any hornet. Nests usually have a maximum of 3 combs and no more than 200 to 300 wasps; in fact, 50 to 60 wasps at any one time is more usual. The photos below show something not commonly seen; a nest of Vespa ducalis not built in a cavity, but in an exposed location under an overhead bridge. This was truly a great opportunity to watch these wasps, and I revisited the site for many weeks; the two photos show it in an early stage and then towards completion. However, since then I have seen and heard of several other instances of such behaviour; it seems that besides underground, this species does sometimes nest under large overhead bridges in Hong Kong.
In Hong Kong, this species has an extremely short life cycle, with queens emerging only in mid-May, and colonies starting to die off in September.
Vespa ducalis is known to be a very mild-tempered species. It tolerates virtually any activity near the nest as long as the nest site is not touched. In August 2006, I relocated the nest pictured above, which by then had around 30 or 40 wasps and 3 combs. When the nest was brought down in a net, the workers that escaped made no attempt to attack, but simply tried to return to the nest. Also, in an attempt to photograph the nest below, which was built in some bushes, I trimmed the bushes with a pair of shears in order to be able to photograph the nest. Since there were no workers on the envelope at that point, I used a stick to brush the envelope in order to get some workers out so I could photograph them on the nest. Only a few wasps emerged; they walked about the envelope, one of them gave the stick a lazy bite, but that was all, and they disappeared into the nest almost as quickly as they emerged. A friend who relocated an underground nest told me of how he simply enlarged the entrance with a shovel, then pulled the nest out with bare hands after stupefying the wasps with smoke! This is incredibly unaggressive by hornet standards! Still, it can give a painful sting (the only time I have been stung was by accidentally squeezing the leg of one), so it would be wise not to deliberately disturb a nest. It may occasionally nest inside houses, in structures such as cabinets or bookshelves. This is very rare in urban Hong Kong, although it may happen in the more rural estates. However, this species is certainly not a major threat to us.
