Look up “anglerfish reproduction”. The males are tiny and permanently fuse themselves to a female, basically becoming a parasite of balls.

Wikipedia:

When a male finds a female, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male becomes dependent on the female host for survival by receiving nutrients via their shared circulatory system, and provides sperm to the female in return.