On holiday in the south west of France we saw some/just one around quite a lot (?) insects that looked like big, fat common wasps. Didn't really have a pronounced waist. My 13-year old nephew, having been taught to sit still if a wasp landed on him, sat and watched one of these big wasps on his arm. While he watched it it brought its mouthpiece from each side together to form a sort of point and stabbed it into his arm! He was left with a small puncture wound (which bled a little) , which was a bit sore, but it clearly hadn't stung him as such as it didn't swell up or anything and disappeared pretty quickly. We think that the same happened to my 7-year old, who was almost hysterical saying that a wasp had stung him, but there was no evidence of a sting (this was before the 13 year old, so at the time we thought he was just being a drama-queen!!). In both cases the boys were wet, having been in the pool. Any idea what these might have been?