Mother Nature is a B*tch.

An article from National Geographic : "Sex Puppeteers" Force Sex Change, Virgin Birth in Bugs via Genes

Fast-spreading parasite species force sex changes on their victims, induce virgin births, and turn animals into "gross monsters"—among other horrors.

Now a new study has decoded how the bacteria may be able to wreak their havoc: by shutting down immune systems.

The parasites, of the Wolbachia bacteria genus, cause a gene in wasps to stifle the insect's protein-based "alarms" against the bacterial invaders, say researchers who mapped the genomes of three species of Nasonia wasp for the first time.

As a result, the wasps' antibacterial defenses are never deployed, allowing Wolbachia to begin their dirty work.
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Males are transgendered into fertile females, or killed. Virgin females give birth—no fathers needed. The sperm of infected males is rendered useless in uninfected females.
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Males get the shaft because Wolbachia can live in eggs but not sperm—only infected females can pass on the bacteria to offspring.

"For the human world this would be science fiction, but in the insect world, it's very much a reality," said Seth Bordenstein, a professor of biology of Vanderbilt University in Tennessee.

Funny things happen to humans too, Professor. Just rarely.

Which isn't to say Wolbachia's handiwork is always spot-on. Sometimes the bacteria can't finish the job, resulting in "gross monsters"—part male, part female—Bordenstein said.

Bordenstein and colleagues don't know exactly how Wolbachia work their genetic sabotage. But they do know that the bacteria go a step further and actually transfer some of their own genes into the wasp's genome.

Gross Monsters - yes, Intersex people sometimes get called that, and worse. In scientific jargon, it's not perjorative, but in the context it's usually uttered to humans, it is.

Interesting that Wolbachia can interfere with the host's genome... one of Mother Nature's more disquieting phenomena.