Their small size coupled with their extremely short lifespan has made male X. vesparum very difficult to study.

They reside in the wasp's body cavity and never develop mouthparts, legs, eyes or wings, and their only form of genitalia is the ventral opening where males can inseminate them, as well as being the point of larval escape.

[7] In the case of the former, they then must locate a foraging wasp using chemical cues, and then grasp on to it and be carried back to the nest.

The exact mechanism for this is unknown, but it is possible that the parasite's surface has chemical properties that allow it to remain concealed from the host immune system, and the ability to moult without ecdysis is likely a method to retain this protection and is a preadaptation for its endoparasitic lifestyle.

[1] The fourth and final life cycle stage is the development to the free living male or neotenic female form, followed by their whole or partial emergence respectively.

[8] Conversely, the female develops into the final neotenic form and extrudes from the host abdomen far enough for the genital opening to be reached by a mate, as well as far enough to allow larvae to escape.

Additionally, the male wasp dies before winter, eliminating the chance of the larvae spreading in hibernating aggregations.

[1] A trend noted in paper wasps infected by this parasite is that they appear to exhibit a strong preference to congregating on Campsis radicans (trumpet creeper) bushes.

Parasitized female wasps feature undeveloped ovaries as well as lowered levels of juvenile hormones and they abandon the colony without performing any of their caste's duties, meaning the host is castrated and reproductively "dead", leading some to describe X. vesparum a parasitoid as it applies to female wasps.