system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Do tiny animals (like flies) have comparably complex digestive systems as humans?

Like I can’t imagine a fly having a small intestine and liver or whatever in such a small body?
gpt
You're right, they don't. It really depends on what  the animal eats and how they've evolved to eat that food.

When you say a human's digestive system is "complex" another way to put it is that we are adapted to eating a wide variety of foods. We have different types of teeth suited for biting flesh, but also for grinding plants. We have a jaw that is fairly strong but not as strong as a gorilla or other apes. We have complex digestive chemicals for breaking down complicated foods like starches but lack the ability digest bones or plant cell walls.

(many) Birds for example don't have the ability grind the seeds they eat, so they have special organs that they fill with rocks that *grind* the seeds into a paste.

Cats and dogs for example, that eat meat, don't have the proper digestive systems to handle lots of sugars.

But, back to your point, most animals, from flies and ants, up to humans and whales, have a basic "mouth (where food is broken down mechanically) - stomach (where food is broken down chemically) - intestine (where nutrients are absorbed into the body) - butt (where waste is removed)" type system. Those specific terms might be human specific but the general steps are the same.

Each animal does some steps differently though, for example humans excrete dead blood cells with our foodwaste which gives our feces that brown color. Birds combine their poop and pee into a whitish paste. Bulls and cows, that eat lots of grasses and other plant matter, remove their waste in the form of political campaigns.