Parasite on Polistes sp.
Thanks to Mattia Menchetti (Italy) for ID (and noticing it in the first place).
Sessile twisted-wing parasite in a wasp's abdominal segment. The animal is really unclear in these images, but you can see the bulge clearly in the first picture, and (barely) the whole sticking-out-part in the second. Unfortunately, taking pictures of a very small part of a big, wriggling wasp in a reflective plastic bag with a clumsy macro lens is rather difficult.
The wasp's observation is https://www.inaturalist.org/observations/2240722 .
I sometimes caught insects in net temporarily, and put the really really flighty and dangerous ones in a plastic bag for ease of picture-taking. They were released.
The Strepsiptera (translation: twisted wing, giving rise to the insects' common name, twisted-wing parasites) are an endopterygote order of insects with nine extant families making up about 600 species. The early-stage larvae and the short-lived adult males are non-sessile, but most of their lives are spent as endoparasites in other insects, such as bees, wasps, leafhoppers, silverfish, and cockroaches.