What type of animal is a wern?

There is no animal known as a "wern". It's possible you've misheard or misspelled the name.

Could you please clarify or provide more context? Perhaps you meant:

* Wren: A small, plump bird with a short tail and a distinctive song.

* Werwolf: A mythical creature that is a human who transforms into a wolf.

* Worm: A long, slender, limbless invertebrate.

Let me know what you had in mind, and I'll do my best to help!