I think that's a ground hornet's nest you dug into. Don't dig into it again if it's warm. I've run into those while mowing and they come out and swarm sting you. I'm relatively immune from bee stings, but I still had mild anaphylaxis.

Les Stroud had a general rule about bugs (from Survivorman series)... if it's slow, stinks and has colors, avoid. It's the bug that behaves as if they're afraid of you that are safest to eat.