My Basset Hound, Cooper

Question
Today when my friend arrived home our basset was rolling in the floor and scratching. We then noticed he had large hives all over him and his head area was swollen. He then ran outside and vomited. We gave him 12.5 mg of benadryl and rushed to the vet where he received IV benadryl and a steroid injection. He is doing fine 7 hours later. I have been through the whole yard looking for ant beds and wasp nests. I found nothing but 2 frogs over by the A/C unit where water was dripping. Is it possible Cooper's allergic reaction was from a frog?  Thank you!!

Answer
Something like that happened to my puppy last year, out of nowhere her face started swelling up until her eyes were almost closed.  I had to take her to the vet for a shot.  Good thing it was taken care of, because a dogs throat can swell up and close and they can die.  We never figured out what caused it, and there was no bite mark area.  I have never heard of a frog causing a reaction.  I am not sure.  It could have been a spider bite, or maybe a bee sting.