You know, I always wondered about that myself. Since garters start out as eggs, and have no connection to the body like mammals do, then why do gravid females gain so much weight? You would think that the already fertilized eggs developing would simply convert some of their weight to the babies and there would be no gain, but that's not what happens.

If there's going to be a gain, I would think it would be as the eggs are being formed in the body, before they are fertilized, not after. I laugh when people say their garter is gravid and "eating for two" so to speak. They are not. The nutrients are already there in the yolks, and have been since conception. And yet, the mother continues to gain weight long after the babies start growing. The only matter exchange happening after conception is gas exchange. That doesn't seem to account for enough weight.