This is a very large hornet, with queens averaging a shocking 43mm to 46mm or more! Males average 35mm; workers range from 26mm to 39mm. It is a well-built, stocky species with a large head, fully yellow in colour. The head is strongly widened when viewed from the front and well-developed behind the eyes, making the eyes look smaller than those of most other hornets (a feature in common with its close relative Vespa mandarinia. The mandibles are large and powerful. The thorax is mainly black with some orange markings towards the rear. The first two abdominal segments carry a large area of bright yellow and orange-brown, while the rest of the abdomen is black.
Above: Vespa soror
Below: Vespa ducalis
The large yellow head, greatly enlarged and widened behind the eyes, and very slight differences in colour as well as obvious differences in size differentiate this species from Vespa ducalis.
This species is found in Hong Kong and parts of South China (Hainan, Guangdong), Vietnam and North Thailand (Chiang Mai). In Hong Kong, it is not a very common species, although it is not rare in rural, unpolluted countryside. It does not generally fly near people, although it is not at all secretive; seemingly confident due to its large size, it flies slowly and conspicuously in the open.
This species is easily confused with Vespa ducalis. In fact, I have been wallowing in ignorance all these years, assuming it was Vespa ducalis. Only recently did I start to notice obvious differences resulting in two different "types" or "colour forms", as well as different predatory behaviour and different colony cycles. Dr. Junichi Kojima from the Ibaraki University, Japan confirmed this species as Vespa soror, which is in fact the closest relative of the well-known giant hornet Vespa mandarinia. In fact, it was once considered a subspecies of this! This also explains its enormous size, head structure and certain aspects of its behaviour.
This species is a voracious predator; workers frequently attack and kill grasshoppers, cicadas, large butterflies, dragonflies and even mantids and large spiders! This species appears to be a voracious predator that will attack and kill any insect it can overpower, and due to its size and strength, few other insects are a match for it. The photos below show a worker about to carry the meat from a dragonfly away, and another tearing into a freshly killed cicada.
Besides this, Vespa soror often attacks the nest of Polistines (paper wasps), like Vespa ducalis and Vespa tropica. However, instead of attacking singly as these other two species do, Vespa soror often attacks in groups! A friend told me of an incident when a very large Parapolybia indica nest in his garden was attacked by several groups each comprising 4 or 5 workers, effectively annihilating the colony in just a short period. And unlike the other two species, Vespa soror often kills the original inhabitants by biting with its huge mandibles. I have also seen a video of Vespa soror entering a beehive and killing the bees one by one with its mandibles, and some friends and bee farmers in Hong Kong have even reported seeing multiple individuals of this species attack beehives in bee farms, effectively killing whole colonies at a time. All this is similar behaviour to that of its near relative Vespa mandarinia!
The nest of Vespa soror is usually underground or in a crevice. Due to the location, the nest is seldom seen. If dug out, the nest usually appears rhomboid or shaped 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 fairly large colony sizes; a nest I have seen at an exhibition had more than five very large, wide combs. The photos below shows a typical nest site of this species, with workers carrying out excavated pellets of soil in order to enlarge the nest cavity.
In Hong Kong, this species has a long life cycle, with queens emerging in mid-March to April, and colonies dying off only in January.
As long as the nest site is not touched or approached closely, Vespa soror workers do not seem to react to human presence. In fact, the colony that I had been attacked by was not of Vespa ducalis, but Vespa soror! Read more about this here; they crashed into my forehead over and over but did not use their stings. However, these wasps can attack ferociously when provoked, and the sting can cause extreme and long-lasting pain. Fortunately, they usually nest in the countryside and well away from human dwellings.
This is probably the second largest hornet after Vespa mandarinia. Looking at specimens in my collection, it is in fact larger than the famous Japanese form, and is only slightly smaller than the Taiwanese colour form, which is generally larger. The photo below shows them together (both queens).
