It's all good.
I see sperm as a seed, womb the soil.
I'm not sure the positive/negative thing works for it. It's hard to find examples of the +/- in the real world. I could only think of electricity. Not sure of the parasite thing.
Believe it or not, lobster and crabs are crustaceans and are a part of the arthropod family, which include caterpillars, cockroaches, and spiders!