Why Are Rats Balls So Big?

If you’re curious about the anatomy of rats, you’ve probably wondered why their balls are so big. This is because male rats have a proportionally large testicles, nearly as large as their heads. The balls are a sign of sexual maturity, as the testicles will not descend until the animal has reached five weeks old.

Rats have enormous balls because they have to compete for sperm in a mating system called polyandry. When female rats are in heat, they breed with many males to increase their chances of fertilization. The larger the testicles, the more sperm a male can produce.

The big balls are a sign of strong competition for sperm. Scientists have studied evolution in rodents to understand the reason. They have demonstrated that the testes of mice can evolve to produce more sperm. This suggests that male rats’ balls may not be as large as their female counterparts’.

During pregnancy, a rat’s belly will grow sideways, which is why they have a sideways belly. The uterus is two-pronged, which is designed to carry many babies. During pregnancy, the baby lies along these horns. The size of a rat’s belly doesn’t indicate how many babies are in a litter, although some people count the embryos in the abdomen.