Xenos vesparum

Xenos vesparum is an insect species, whose females are permanent entomophagous endoparasites of Polistes paper wasps. They dwell their entire lifespan in the abdomen of the wasp. Two particular species of social wasp it has been known to infect are Polistes gallicus and Polistes dominula.[1] Younger members of a wasp colony tend to be targeted, although X. vesparum displays parasitic behavior in all stages of this host.[2]

Xenos vesparum
Male Xenos peckii in its winged insect stage (1), and female Xenos rossii in its neotenic stage (2).
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Strepsiptera
Family:	Xenidae
Subfamily:	Xeninae
Genus:	Xenos
Species:	Xenos vesparum Rossi, 1793

According to Fabio Manfredini of Pennsylvania State University, co-author of an animal behaviour study of this insect's odd life cycle, published on 8 October 2011, the parasite infects a European paper wasp and completely alters its worker caste behaviour. The infected wasp begins to suffer nutritionally, then flies to meet with other infected wasps. The male parasite, which pupated in the infected wasp, exits the wasp's abdomen as a winged insect and mates with the female parasites which stay inside their host. Wasps infected with the male parasite die. Wasps infected with the female parasite then fatten themselves up much like queen wasps do. They then fly to meet with other uninfected queen wasps. Then when the parasite is mature, the infected wasp flies to mingle with other uninfected wasps, thereby spreading brood and larvae into new environments.[1][3][4]