common name: human bot fly, torsalo (Central America), moyocuil (México), berne (Brasil), mucha (Colombia), mirunta (Perú), and ura (Argentina, Paraguay, and Uruguay)
scientific name: Dermatobia hominis (Linnaeus, Jr.) (Insecta: Diptera: Oestridae)
Friend had a welt for a while. Turned out to be a bot fly. The welt looked like a thrid nipple for a while. See photo
He finally messed with it enough that he was able to pull it out and flung it on the floor.
Where upon it made a bee line for the door.