The world's biggest rodent has arrived at Wellington Zoo, but it's not as ugly as you might think.

Capybaras will be unveiled at the zoo for the first time today, with one male and three females having recently arrived.

The South American rodents are the world's largest, and are considered very social and excellent underwater swimmers.

It's great timing for the zoo, which is celebrating its 110th birthday.

To celebrate, the 110th person to enter the zoo each day this week will do so for free.