sting

I just noticed a weird circular mass on my 6 month old boxer puppy. Has anyone seen anything like this? He was chasing bees yesterday so I wonder if its a sting? Or something more serious... I plan on calling my vet but thought I'd ask here now just to see if anyone has seen anything like it.

Our bosses dog (whom we are babysitting for a week) loves to romp in the grass and once in awhile will graze for a minute. Yesterday she chomped on a wasp and got stung. Her whole face got swollen and while the swelling did go down, you can see where she was stung on the side of her lip. And...