In summer, I often encounter hornets (Vespa crabro) in the forest near my home town in The Netherlands.
They are seriously big, up to 3.5cm (1.4"), so they are not easily mistaken for common wasps. They like to live in hollow trees, and they use their powerful jaws to enlarge their nest and build the internal structure with cellulose fibers they chew off trees.
Here's a photo of a nest entrance I shot near the local peat bog, the Aamsveen, which is just to the south-east of Enschede, The Netherlands:
Olympus XZ-1, 112mm, ISO100, f8, 1/125s, three-photo montage from hand-held shots of the same tree
It's a busy coming and going, and it is not a good idea to get too close, even though they will warn you well before they start to sting.
Inside the nest, usually started in May, there are workers and a queen. In August, the queen starts laying eggs that will grow into new queens and males in stead of workers. These new queens mate and fly out to find a place to hibernate until May. The males die shortly after mating, mostly without ever having left the nest.
The workers and the queen feed mostly on tree sap; they specially seem to like oak trees. They look for a damaged tree and use their jaws to keep the sap flowing. Here you see a few doing just that:
Olympus XZ-1, 112mm, ISO400, f4, 1/40s
The photo above was taken in May, early in the season, and the bottom one of the three is not a worker, but a queen that hasn't started a new nest yet. It's not often you get to have a look at a queen, as they don't leave the nest once they are settled.
Here's a close-up of this queen (3.2cm (1.25"), this one was) in the same location, feasting on the sweet oak-tree sap:
Olympus XZ-1, 112mm, ISO100, f8, 1/125s
The queen and workers can feed themselves off tree sap, but the larvae need proteins. This is why hornets hunt other insects. You can often see one (they hunt alone) near flowers, not to eat there but to catch the insects that are attracted by the flowers.
When they catch an insect, they strip off all the inedible bits, leaving a nice, clean fillet for the larvae. They use their jaws and front legs for the filleting, and they seem to find it convenient to do this hanging from their hind legs. When you're lucky, as I was, you can catch one in the act:
Olympus XZ-1, 112mm, ISO100, f6.3, 1/200s
Many people seem to think hornets are very aggressive, but despite their size and fierce looks they are actually far less aggressive than most other wasps. They generally avoid confrontation and will only attack if you touch them or when you get too close to their nest or feeding places. Even then, they will usually first do some swoops past your head, buzzing loudly to warn you off. If you retreat, they will leave you alone. If you don't, you have yourself to blame; their stings are very painful.
Thanks for watching and reading!