Traumatic Insemination
Male bed bugs bypass the female's reproductive tract entirely, stabbing through her abdomen to inject sperm directly into her body cavity.
Bed bugs practice one of the most violent mating methods in the animal kingdom: traumatic insemination. Males don't use the female's reproductive tract at all. Instead, they pierce the female's abdomen with a needle-like penis and inject sperm directly into her body cavity.
The sperm then travels through her blood to reach her ovaries. This process is so traumatic that it leaves permanent scars on females, and excessive mating can significantly reduce female lifespan.
Why did this brutal system evolve? One theory suggests it gives males an advantage in sperm competition — by injecting sperm directly into the body, they bypass any female defenses in the reproductive tract. It may also be a form of manipulation: the wound and stress may cause females to lay eggs sooner.
Females have evolved some counter-measures: many species have developed a specialized organ called the "spermalege" on their abdomen where males typically pierce. This organ has immune cells and may help reduce infection from the wounds.
Some related insects have evolved similar traumatic mating systems, suggesting it's evolved independently multiple times — a disturbing example of convergent evolution.