Family Empididae, Dance Flies.

Don't know about the dance part -- to me, this is a really gorgeous fly with long long legs.
Wikipedia says they feed on other insects AND nectar and pollen! I never heard of a carnivorous
pollen-eating fly before. Other photos of this species show males probing for nectar.

This is a male of genus Empis, probably E. livida, a widely distributed species in North America and Europe.
Males are said to present prey items to females as a courtship gesture -- maybe that is what is happening here.

Also note: this family is better termed "Dagger Flies;" the true "Dance" flies are now considered a separate
family, Hybotidae (another example of how much taxonomic work remains to be done on order Diptera).