Great Black Wasp

I've been interested in bugs my entire life (being a gardener) and always lived in town. Now I've been on a farm for 6 yrs and still amazed by how many bugs I've just recenly discovered. One in particular is a little scary. I was mowing our lane (driveway) and about a quarter mile from the house. Suddenly a huge black thing started flying near my riding mower. Being afraid of wasps, I stopped and watched it warily, wondering if I should run for it. It seemed more interested in the engine than me. It made about 5 passes within 3-4 feet of the front of the mower, then zoomed away over the corn. I've seen it (them?) several times since then, usually 50 yrs or more from the house. It flies very fast, almost more like a hummingbird than a wasp... but it's not THAT big. I haven't seen one sitting still, so it's a challenge to accurately describe. It seems blue-black like a mud dauber, and a few inches long with a couple bulbus body parts like a lg wasp. I don't know of a nest anywhere, which makes me wonder if I should be wary or if it was just out hunting. I usually run screaming from wasps, the only insect I can't stand to be near, and would hate to get stuck so far from the house with no defenses. Is the Great Black Wasp common in eastern Iowa? I can't believe I never knew of these before now.
luchiaan