Drips and Drops An animal doesn’t always need a lot of water to cool down. T at’s a good thing for a wallaby. It lives in Australia’s outback. Sometimes, it doesn’t rain there for weeks. T e sun beats down. T e heat rises. T e wallaby stands on its hind legs. It looks
for shade or water. It doesn’t see either. Yet it isn’t in trouble. T e wallaby licks its paws and its arms. In
the hot air, its saliva quickly evaporates. As it changes from a liquid to a gas, the spit absorbs some of the wallaby’s body heat. T at cools the wallaby down.
Sweet Sweat Something similar happens when you sweat. T ink about running a race. You start to get really hot. Before you overheat, your body’s cooling system kicks in. First, your brain sends a message to your
sweat glands. You have 2.6 million of these glands tucked under your skin. T ey make a solution of water, salts, and other chemicals. Soon, millions of drops of sweat squeeze
through pores, or tiny holes, in your skin. Sweat coats your skin. When it touches the air, it quickly evaporates. As it does, it takes extra heat from your body with it. You may feel sticky and sweaty, but you also feel cooler. Dogs have sweat glands, too, but only in
their paws and noses. If a dog gets really hot, it can’t sweat enough to make a diff erence. It’s got another way to keep cool, though. T e dog opens its mouth and lets its tongue
hang out. Saliva drips from the dog’s tongue. As it pants, air rushes over its tongue and into its mouth. Some of the dog’s saliva evaporates, cooling the dog down. Birds and many other animals pant, too.
Fast Fact: A dragonfl y stays cool by standing on its head.
6 NATIONAL GEOGRAPHIC EXPLORER
Busy Bees Insects can’t sweat. Yet a honeybee still uses evaporation to keep cool. Imagine a hot summer day. Inside the hive, thousands of worm-like bee larvae lie helpless in the heat. If it gets any hotter, they could bake. T e adult bees rush outside. T ey take their
body heat with them. T e temperature in the hive drops a little. It’s not enough, though. A few bees buzz off to find water. When
they find it, they return and do a waggle dance. T ey tell the other bees where to go. More bees race off to gulp drops of water. T e drops slide into the bees’ honey sacs. T is body part is like a second stomach. T e bees use it to carry the water back to their hive. T e bees line up around the hive. T ey all
face the same direction. Each bee burps up a drop of water, opens its mouth, and holds the drop on its tongue. T e water evaporates, cooling the nearby air. Wings vibrate, pushing this air toward the hive. T anks to this bee breeze, the temperature inside the hive drops and the larvae are safe.
In this pose, sun hits just a small part of the dragonfl y’s body. It doesn’t get too hot.
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