Twisted-wing parasites start out life as tiny larvae. Very tiny. "Can crawl right inside a bee, silverfish, or cockroach" tiny. Once inside a host, their mere presence causes their host's genitals to straight-up vanish, in the most dickish magic trick since Batman drowned Wolverine. Please note that we haven't even gotten to the worst part about twisted-wing parasites yet, despite spending the previous two sentences describing how they make genitals disappear.
Once they grow up big and strong (relatively speaking), the male twisted-wing parasites leave their host and fly off to fulfill the singular mission of every single pubescent male in the animal kingdom: have as much sex as possible before they die of a spontaneous dick explosion. The problem is, female twisted-wing parasites never grow wings. For that matter, they never develop much past the larval stage, or even leave their host. So how do they bone? In the most terrifying manner possible. The females jam their backsides outside of their hosts' bodies, turning them into walking vagina bouquets, like Cronenbergian pornography.
Woo-wee, look at all them pieces of ass.
And in case you're still planning on sleeping tonight, in some species, the females have entirely given up on concepts such as "normalcy" and "the having of genitals." Among these varieties, the males are forced to impregnate the females using the old stab 'n' squirt method, better-known to science types as "traumatic insemination" and to everyone else as "the facehugger method." Then, during pregnancy, the ungrateful little shits cannibalize their mother from the inside out before emerging to start the cycle all over again.