I have them come out twice a year, middle of winter on bright sunny days and Spring, when they cover the ground in a mass about 100 x 100', the ground looks like a fluid rust moving. And yes, they do bite when they're hungry, kinda hurts but short lived pain.
Well, turns out these little critters can fly at least 9000' high while migrating to the valley floor from the Sierra.

Check out this 80 mile wide swarm, that's Right, 80 freakin miles wide.

https://www.youtube.com/watch?v=aAbLskXc_Jk

Here's the actual radar cloud.

https://www.youtube.com/watch?v=U9UoTjOmJaQ