[Heel n Toe]

I'd guess it was a wasp and when you closed your hand around it and the sponge, the stinger broke off. Something similar happened to me a coupla years ago when dumping a water dish while feeding/watering our neighbor's cat for a few days while she was out of town. I didn't see the small brown wasp in the dish and it hit me in the "webbing" between two fingers.

The pain was so immediate... it went right through me like an electrical shock. I don't remember a lot of swelling, but it hurt for a day or so, and then the worst part happened.

The itching. Ugh. It was relentless. I think I remember Benadryl helping a little.

It might be a good idea to call a pharmacist and ask if there's anything you can get for it right off the shelf.