Little white skinned members of a great barbarian tribe that live in a huge village known as Epididymis
. These barbarians, after falling victim to an "earthquake", go on a great quest to find The Great Orb(the female's egg). They pillage every village along the way, fight random soldiers, and carry on their normal routine until they find what they're looking for.
Eventually these little devils find the orb in question and it selects the greatest warrior out of all 10 million of them. It then rips that warrior apart, uses his DNA, and kills all if his friends with a huge wave of random acid.
And yes that warrior that was selected was you. So anytime u feel bad or feel low, just remember that u were the greatest once.
This entire journey of the sperm takes place within about 1-4 days.