This was at night in a forest park near Nogata, called Tsurugi-dake Natural Park (map here), and it’s a great place to find stag beetles (kuwagata) and Japanese rhinoceros beetles (kabuto-mushi).
I found two species of hornet (and lots of other things!) feeding on sap this evening. The larger one is Vespa mandarina (oo-suzume-bachi) and the smaller one is V. tropica pulchra (kogata-suzume-bachi). By the way, the metallic scarab beetles in the picture are Rhomborrhina japonica (kanabun).
Vespa mandarina is known as the Asian Giant Hornet and not only is it the largest hornet, it’s also the most venomous insect in the world (per sting). Lucky for me that this one was more interested in the tree sap than my thumb!
There’s an interesting article about the Asian Giant Hornet on wikipedia.
Vespa mandarina japonica = oo-suzume-bachi
Vespa tropica pulchra (synonym V. ducalis) = kogata-suzume-bachi
Link here to a page explaining the differences between the two species (in Japanese but with pictures).