Do hornets always have nest in the trees? Can they be in the ground?

Question

Do hornets always have nest in the trees? Can they be in the ground?

Answer 1

Different varieties create different types of nests.  There are true hornets and wasps.  Yellow jackets build nests in the ground, while bald faced hornets usually build aerial nests.  The website below is helpful in determining if you have yellowjackets or hornets.  There are other sites as well - Wikipedia has a good article on hornets.