I think this is a hornet which often visits delfinium flowers that are in bloom now to get their nectar. Some people say it's not a hornet, so I am really not sure it is or not. They work very hard to get nectar. When I observe them hard, I find they prefer deep flowers which they need to get in to get the nectar. For example, delfiniums and Nasturtiums etc.
I guess those flowers hold very yummy nectar :)