It takes less time to invent an animal than a humanoid species, gods, or even monsters because animals aren’t as complex. Plants are even simpler. First we’ll consider whether we should invent them or not. Then we’ll look at specifics for each and then considerations that apply to both.
Appendices 5 and 6 are templates for creating a plant or animal respectively. They include more comments and advice, and editable Microsoft Word files that can be downloaded for free by signing up for the newsletter at https://artofworldbuilding.com/newsletter/
Should You Create Plants and Animals?
Creating plants or animals unique to our setting is one of the more optional world building tasks for fantasy, where no one expects it or will complain if we don’t. We tend to assume a fantasy world is much like Earth, with the addition of elves, magic, and monsters, for example. We can create just a few plants or animals, tons of them, or none at all. Given that it’s optional, we can benefit from thinking about why we’re creating them, which is the focus of this section.
In SF that takes place exclusively on space craft, we can ignore the subject altogether unless the ship is from Earth or if we want to comment on what the crew are eating, for example. Or if they have an area similar to a greenhouse, zoo, or nature preserve for the same reasons we have parks in major cities: respite from steel, plastic, and concrete surroundings.
In SF that takes place on non-Earth planets, or ships originating from them, we can’t expect the same plants and animals. Even if the world is Earth-like, the life could be very different. Something that looks like a bear at first glance might be an herbivore that makes a good pet. Details are what distinguish life forms from each other.
Vegetation doesn’t need to be wildly different in basic form; there will still be trees, shrubs, and flowers, for example, but we have the option to imbue them with new properties, colors, and significance. This is fairly easy and maybe even necessary to be believable, but we don’t need to invent an entire ecosystem.
Similarly, animals from another planet will still fall into broad categories like fish, amphibian, mammals, birds, and more. Since animals move and are prey and/or predator, behavior becomes an important aspect of inventing something different from an Earth analogue. For example, a horse with two more legs will strike the audience as exactly that. The appearance, size, temperament, and behavior of such a non-Earth “horse” (we’ll want to call it something else) should likely be different in meaningful ways so the audience does not have that reaction. Details are how we achieve this. How to do so is discussed more in the next section.
What is our purpose with inventing this life? Do we need an animal that’s based on an Earth one but which has physical or behavioral attributes that Terrestrial ones don’t? Our characters might use a horse-like animal or giant bird for travel. Maybe we need a lion that can be tamed and ridden like a horse. We might need a snake for its venom that an assassin will use. We might have a humanoid species that wears a bear pelt, except that in the absence of bears, we need a similar (but not too similar) animal. Perhaps we have a wizard who needs a rare plant for casting a deadly spell. And most common of all, we could have either a plant or animal that preys upon our humanoid species. Having a goal helps.