Oh mercy! I had chiggers when I was in college back in 1673! They were awful. they itched soooo bad and I scratched them at night in my sleep and the ones on the backs of my legs got infected. I thought they would never heal. Fortunately no scars 'cause i had nice legs when I was young.
Calamine lotion helps on people - dont know about pets. I had to get UV light treatments. OH I had forgotten how awful that was. Icky!
Yes, there is a spray for them and some granules that you can put on your grass to kill them. Sorry i don't know what it's called though. Good luck!