Uta,
this is a male Vespidae, subfamily Eumeninae.
It is a male because of yellow clypeus, extracted genitalia and hooked antennae.
Try the subforum "Aculeate wasps and bees / Bienen und Wespen".
I have never seen a male posing like this with genitalia poked out!
I have seen something vaguely similar in a tiger moth (Arctiinae) which emits pheromones, although they are not the genitalia, try an image search for "Creatonotos gangis".
And see this one:
http://www.wired.com/2013/12/this-is-not-a-penis/Do not be put off by the url - it is purely academic!
Regards,
Øistein