Which organisms are extremely small and use hosts as both home and food supply

The organisms are a type of pathogen called a parasite. Parasites thrive, by hitchiking on a host organism. The host usually provides some sort of protection, and just as well nutrition and either through directly eating from the host (ticks and blood, or Brain eating amoeba and brain tissue), or stealing nutrition from the host's digestion like the Tapeworm. 

Usually most parasite would be considered harmless, as they are merely looking for food and shelter. However this does interfere with our bodily processes which can be dangerous and cause illness. 

I’ve personally felt invisible all my life, especially when a friend turned out to be fake and didn’t seem to take any type of interest in what i said or any type of input i said. being invisible is a terrifying feeling to experience due to the fact you feel like no one sees you and just sees you (sorry if that doesn’t make sense). it’s like a deep emptiness that no one can fill, just you; you have to fix that emptiness by yourself and you don’t really want , or in some cases want to be invisible. i can see many invisible people when they intentionally stay away from people that can potentially hurt them in any way. also, when a person intentionally breaks off a connection so they aren’t seen by people.hope it

They break down fat