I was just north of New Vegas trying to look for something for whatever quest I was doing. I got a bit lost but I wasn't particularly worried. All I'd seen were Viper gang members and they're not particularly bad. I saw several red blips on my compass but I couldn't see anything and I couldn't VATS them anyway. I assumed I hadn't been detected and carried on walking.
BZZZZZZZZZZZZZZZZZZ. Huh? What's that? Bloatfly? Bah, can't see anything. I'll carry on.
BZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ.ED-E HAS DIED.
CASS HAS DIED.
What the hell is happeni--
Before I can turn around I slump to the floor dead. I didn't even see what killed me.

My first ever meeting with cazadors.
I'm not even going to get started on the Radscorpion Queen. :nope: I'm a massive entomophobic.