The animal kingdom is full of many strange animals that can be found on nearly every corner of the planet. If you live in North America, chances are you’ve seen one of these strange animals at some point in your life, probably during the summer months.

The Luna Moth is a large green moth that can be found from Alaska down to southern Mexico. Its lime-green color makes it nice to behold, and its four-and-a-half to seven-inch span certainly makes it noticeable. But the thing that makes the Luna Moth one of the strangest creatures in the animal kingdom is that it doesn’t have a mouth.

Well, it does actually have a mouth, it just doesn’t use it. If only that were the case with some people! One can only dream. But let’s get back to the Luna Moth.

Luna Moths do have mouths, but they are nonfunctioning “vestigial” organs. Many animals, including us humans, have vestigial organs. In order to understand what a vestigial organ is, just consider the origin of the word—vestigial comes from “vestige,” which refers to something that is left over or behind. Therefore, in animals, vestigial organs refer to organs that no longer have a practical function because the species has evolved past the point of needing or using them. The appendix is an example in humans, while the dewclaw is an example in domestic dogs.

I know what you’re thinking: How could a mouth be a vestigial organ for any animal?

The answer comes down to the very short and diverse life cycle of a Luna Moth.

Like all butterflies and moths, the Luna Moth lives most of its life before becoming a fully-grown moth. A Luna Moth will spend about two weeks as an egg, two months as a larvae (caterpillar), and ninth months as a pupae before entering the world as the winged adult that we see flying around.

Then after a week, it dies.

When the Luna Moth is a caterpillar it consumes enough food for the rest of its life cycle. It stores the energy it needs for its adulthood as fat but doesn’t need to eat anymore. As an adult, the Luna Moth’s only purpose is to reproduce.

Then it dies, presumably happy.