Hornet grubs are carnivorous, the adults bring them prey which consists mainly of other insects. This is chewed up into a paste by the workers and queen and fed to the grubs. As many of these prey items are regarded as "pests" by gardeners, it is clear that the hornet should be regarded as the gardener's friend.
Adult hornets prefer sweet foods such as nectar, and as the adults feed the grubs the grubs exude a sweet liquid which the adult wasps lap up. Towards the end of summer when the queen has stopped laying eggs and all the grubs have hatched into adults, there is no more need for the adult hornet to bring back insect prey, and no grubs to give the adults the sweet substances they crave. So the adults go out and search for sweet substances.
Flight speed of hornets
Hornets are speedy fliers with a flight speed of 6.0 metres per second and 100 wing beats per second. Compare this with other insects.They are expert fliers and can fly up, down, forwards and backwards.
The larvae are carnivorous eating chewed up bits of insects fed to them by workers. In return the grubs exude a sweet secretion in their saliva which is lapped up by the adult hornets.
The lifecycle is similar to that of bumblebees, and the queen will have mated the previous summer/autumn.