Water Bugs in Alfalfa??

I found a black bug that looks like a larger version of a blister beetle in our Colorado or AZ alfalfa tonight. I called my hay guy who said they had seen them but they're Water Bugs. The hay is super rich some of my horses aren't finishing it. I can't find ANY information on Water Bugs on water Bugs in Alfalfa online anywhere. Can anyone help me out? No one is sick but I'm fretting.

Water Bugs in Alfalfa??