That's too bad! I have just missed those underground nest several times and I thanked my lucky stars! Our BO wasn't so lucky last year at team penning, as his horse was stung and he was unseated and broke his arm. I hope the two of you are ok.
Eek, that must have been scary - did you guys get stung? I am super paranoid about wasps/bees as we get a lot of nests around here in summer and after being stung quite a few times this year I have developed a nasty allergy to them and swell up like a balloon. My boy is a very calm horse but I do worry about him getting stung and what his reaction would be - I think it would end with me on the ground.
I am on my knees thanking my lovely armadillo family that clears our area.... I will gladly put up with my plants being dug up if only for this reason. I bless the spiders, even the black widows that take care of the wasps in post toppers and various other areas. I am also in Stumpy's (rat snake) debt for the removal of the rats, mice and various other critters that wreak havoc in the barn.
So sorry you ran into them. Hopefully you are both doing well.
Both him and I got stung a bit, he threw some little bucks while I was on him, but was able to get off before he went into his big bucking spree. Lol but ouch I forgot how a wasp sting felt like. Lol haven't been stung in a few years! I felt awful for my horse, poor guy got most of the stings. :/