My friend Tirill told me a few years ago about some interesting strategies with regard to reproduction. I´ve retold this story countless times at parties and to friends, seeing as how it´s an excellent example of how interesting and absolutely weird biology can be. (I´ve had this story confirmed by Tore Slagsvold, one of my professors in behavioral ecology, who does a lot of interesting research on fidelity in birds.)
In many rodents, it´s quite common that after delivering the load, the male will squirt some sort of gel plug . In doing this, they effectively block the uterus for sperm delivered after their own, like a diaphragm. This is quite a clever strategy. If you can´t be sure your partner is faithful, just give them contraception without them knowing after you´ve impregnated them yourself. In this way you can ensure that those pesky kids she forces you to care for and feed really are your own progeny.
And that´s not all. Apparently, in at least one species of squirrel, the female has somehow discovered this. After fornication, she´ll hop along and when in privacy, either pulls out or squeezes out the plug. Then she´s free to run around and collect more lovers who will all try to help her out with her kids, all thinking they´re exclusively theirs. Girls rule.
Sadly for womens rights, this method of blockage is quite widespread in the animalkingdom, as it ensures a first come-first serve policy that will be transferred to all following generations. In many insects, similar methods are employed, but here, the ladies aren´t quite as lucky. The males eject a chemical mix that will harden to a cement-like structure, completely hardening and blocking any access at all for later suitors.
But in one species of insect, the bedbug(Cimex lectularius) sneaky-sex-strategies has been taken to a whole new level if you ask me. (I don´t have a reference for this, but my Professor in Evolutionary Biology (Glen-Petter Sætre) told us in class.)
Apparently, the bedbugs don´t fornicate like regular folks with the male injecting sperm into a vagina or at least in the vicinity of female reproductive organs. No, he pokes her with a stinger and injects the sperm into her circulatory system. That´s right, into her body. From there, the sperm are carried throughout the body until they reach the appropriate area, enter there, and fertilize her eggs. Wow. And this allows for a whole new version of cock-blocking.
Since the boys don´t have to have access to a female reproductive organ to feel satisfied, rape amongst males is quite common in this species. Now, one might think that this would be at a cost to the males, as they would be wasting valuable sperm on someone who wouldn´t give them any babies. But actually, the sperm enter the circulatory system, travel through the body and to the unfortunate recipients reproductive organs, entering his testes and mixing with his own sperm. So the next time that fella is out on the town and getting lucky, he might be getting lucky on behalf of his attacker.
Now that´s weird.