When I was a kid in Oklahoma, there was one year that there must have been millions of them. Although they look fearsome, that didn't seem aggressive at all. Kids started taking them to school to find out what they were, and that's when we found out they were called cicada killers. We were told that they often appear en mass about every seven years, but we never had a repeat year with that many. I've found since, some areas have an appearance from them every year.
Cicadas are what we Okies called "jar flies", and were favorites with the kids. They were easy to catch, and you could keep them quite awhile in a jar as a pet. The year we had the cicada killers, they weren't easy to catch, because the cicada killers were so good at catching them first.