London Zoo’s yearly weigh-in is a bit like a giant birthday party for the animals, but instead of eating cake, they get measured on special scales. Why do zookeepers weigh them? It is simple: weight tells us if an animal is healthy! If a penguin or a snail is too heavy or too light, the zookeepers can make sure they get the right snacks or medicine. How do they do it? The zoo uses some very clever tricks. Some animals walk onto a scale that looks just like their home, while others are gently lifted onto kitchen scales. Even a tiny bug called a katydid, which is only 6 cm long, gets weighed on a teeny-tiny scale. Meet Gizmo and Kiwi, the London Zoo’s capybaras! They are the world’s biggest rodents and love snacking on fresh plants. Kiwi weighed 45 kg and Gizmo weighed 50.5 kg. Keeping track of their weight helps them stay happy and healthy. Snails get a turn, too! A Giant Magnolia Land Snail weighs about 102.5 g, which is the same as a small apple. The tiniest snail, called a Partula, is only the size of a fingernail and weighs less than 1 g. Even these little creatures are super important for scientists. Penguins are part of the fun as well! Keeper Jessica Ray weighs Humboldt penguins, which come from the coasts of Chile and Peru. Knowing their weight helps the zoo make sure they stay strong enough for swimming in cold seas. All these numbers go into a giant computer database that scientists all over the world can look at to learn how animals grow and how to protect them in the wild. Did you know? One kilogram is about the same as a small apple. That means a 50 kg capybara is as heavy as 50 apples! You might wonder: why weigh snails? Because scientists want to learn how they grow and how to keep them safe. It takes about a week to weigh every animal in the zoo! Plus, visitors can often come to the zoo during the weigh-in to see the animals in their habitats. By learning about the animals’ weight, you can see how scientists keep wildlife healthy. Remember, these scales aren't just for fun—they are an important tool to help us protect animals everywhere!