From my world building notebook for Stuff Blowing up in Space.
A female-only species similar in appearance to humans, the sish reproduce by drinking the blood of a male carnivore when they ovulate. They are sexual predators in the biological sense, that is, they entice their prey with pheromones and simple seduction. They are biologically advanced, physically and mentally, and are even more genetically diverse than humans because of the DNA sequencing used to fertilize their eggs.
While sish are omnivores, their sexual response is tied not only to each other, but also to feeding, making other intelligent species their prime source of live blood and amusement. For the loss of some blood, other species in return receive mind-blowing sex. Sometimes, however, a sish will feed until her source of food dies, either on purpose or by accident, making travel in sish space both pleasurable and dangerous.
Sex dominance is always an issue with sish. Lovers always have a dominant/submissive pairing, and the social structures they form are more advanced than humans, but not necessarily more productive.
Sish seduction biology can create symbiants out of females from other species, exchanging blood for sexual pleasure on a regular basis instead of the infamous sish one-night-stand. Such bonding is rare, but as humans and sish mingle, the number of symbiants has increased steadily over time.
To sish, live food is sex, the more intelligent the live food the sexier it is. Sex is also power, and while the sish consider themselves biologically superior to other species, culturally it could be argued some of their core planets are stagnant, as this excerpt shows.
Princess Oneesha, heir to the throne of Jephinae, could not believe what she was hearing from the Queen.
Oneesha had been crying. Crying for her sister. Crying because she was hungry. Crying because she needed sex. Crying in frustration. Now she was crying in anger as the Queen assailed her ears, angry because Oneesha would not answer her summons and that the Queen had to come to the Princess’s bedchamber.
What the Queen had to say shocked her, all the worse because she almost said yes. Now, Oneesha was angry with herself more than the Queen. “Mother, I cannot partake in the ceremony now! It is out of the question! Crazy humans have kidnapped my little sister! How could you think of such a thing?”
Her mother backhanded her. Hard. She fell to the ground, spots in her vision. The Queen was a very strong sish, and her face throbbed as if it was on fire.
“Do not prattle on with your insolence! You don’t understand the tenuous hold we have, we need to bond the power-players to you or there may not be another ascension ceremony! Ever!”
From the ground, Oneesha stared at her mother. That’s when she knew.
“You’re pregnant,” she blurted out.
The Queen flinched back as if she received a punched in the gut.
“That is no concern of yours, daughter,” she said dismissively.
Oneesha stood up. “It’s true! You were starving her! My sister snapped because she has chaste sickness. It doesn’t matter that I’m older; she was always stronger than I was, more developed. Yet you went ahead and arranged my ascension knowing she was dying! You decided since you were pregnant, you didn’t need her around anymore. That having her die of chaste would make people fear you!”
“People do fear me, as you should.” The Queen advanced.
Oneesha drew her ceremonial dirk and pressed the button on the hilt. Dark fire ran up and down the blade, the deadly hum of its vibro-blade filled her bedchamber.
The Queen stopped, eyes narrowing. “I can take that blade from you, child. Do not be stupid.”
“Lay hands on me again and I will cut that daughter out of you and feed her to the servants.”
The Queen stared.
“So it’s come to this? Treason?”
Oneesha burst out laughing and turned the blade off, sheathing it. “It’s only treason if you admit your weakness to Palace Security. Then what? You’d have no daughters except the one in your belly. Your hold on the nobles would come crashing down sooner rather than later.”
She turned and walked from the room.
“Where are you going? Come back here!” the Queen shrieked out.
Oneesha turned and looked over her shoulder.
“I’m going to find my little sister,” she lied, the first lie she had ever told the Queen.
“Good bye, Mother,” she said, walking away.