Very little, almost cell-sized anthros, living inside bodies called "cities". Each "city" has one "care taker that makes sure everything is ok and the host is healthy. The benefits are that the tiny anthros have shelter, and the host (who knows nothing about this), is a little bit healthier thanks to the germ police.
Citisents travel from "city" to "city" with special buses-aeroplanes. They take electricity from their host's blood. They have long potruding towers in the blood vains that the blood cells rub against and create an electric charge (thanks to brother captain stern for this part)
Special scientists gather food from the host's stomach, process it in factories and sell it in the market. Because no hosts eats all kind of foods, care takers will export and import goods from other cities. The city's waste is carried and mixed with the host's own waste. The amount is so small that its not detected even by analysis. Special lights simulate night and day.
The care taker's main office is usually located in the head, where he can monitor everything. Normal citizents don't know they live inside a body.
When Babe got shot, his care taker, Bard refused to abandon him, so as he was turned into a robot, his care taker had his helpers to do the same to him. They then, abandoned him. Bard then proceeded to create a series of nanobots to live inside Babe, and slowly, he build an entire city (see the story stranded)
Both male and female models are extremely strong - females are perfect for more "delicate" works around the protector's body. They are just as durableas males, and their lighter body - frame makes them faster than the male models.
Even though nanos are made of metal (harvested by the Protector),they still have facial expressions and eyebrow movements like a fleshy anthro would have. They even have tongues.
Having children: Nanos do not mate, as in, they do not have sex. If a pair wants a child, they file their request at the Population Control Center and if their request is accepted they receive a small nano baby.
Growing up and upgrades: Metal can not grow on its own. When it is the time for the child to "grow", the parents reiieve "upgrades" from the factory. Other upgrades a nano can make, can be "work-out" upgrades on a particular body part(s)-depending on what/how much time the nano has excersized that body part. Those upgrades usually dont alter the appearace of the nano, but it increases strength in that particular body part. Those upgrades are "muscle" upgrades. Other upgrades can be for appearance purposes, like "tattoos", body mods. etc-anything normal people do but in a metal world.
Currency: Nanos use no currency. They will exchange services/products with other services/products/
World view: Unlike care takers, nanos are aware that they are inside a living robot. And again unlike the care takers, nanos are made from material from their host, so in a way they feel like they are part of him. Removing a nano from the Protector, will be a punishment worse than death.
There's a huge difference between care takers and Nanos (except the organis-metallic one). Care takers are NOT part of their host. They move inside a city and occupy it, A nano is made FROM parts of the Protector himself. If a nano would be forcefully removed from home he would suffer more than a care taker.