Bad Wasp, Good Penny?

I was talking to Leslie yesterday evening [afternoon in the Bay Area] when she said, "Ow! That little bastard!" "What happened?" said I. "Wasp stung me." "Put a penny on it." I had read this bit of folklore a few months ago and told her about it. "Let's see," she said. "Does it have to be shiny?" "I don't think so." "Oh, it stings." "Maybe that means it's working. You need to keep it in place at least 20 minutes. Got a Band-Aid?" "No." "A handkerchief?" "Are you kidding?" Well, a scarf." After a bit, "I've got a fabric belt." And we went on to talk about weightier matters than wasp stings. Except a few minutes later when she asked rhetorically "Why'd he have to sting me" "He's a mean, nasty critter who hates you." "I hate him too." I asked for an update and hoped for an email today. Nothing.

I've forgotten the source of this bright idea but now I'm curious about it. I'll update when I get more info. There's also the paste of baking soda for wasp and bee stings too, part of a whole list of wonders baking soda performs. We'll see.