I was thinking bald faced hornets, they can be very nasty. I have run into them numerous times when trout fishing, the nests are built over the streams. Our main enemies here are yellow jackets and fire ants, they can be very dangerous in large numbers. Not sure if the dry weather is driving them close to homes or not, but we've had a terrible time with them this year.
Another somewhat dangerous insect we are seeing more of is the velvet ant or cow killer. They are huge, have a strong venom, and can sting multiple times. It is actually a wasp.