An insect is a small animal with six legs, three body parts, and usually two pairs of wings. Insects include ants, bees, butterflies, beetles, flies, and grasshoppers. They're the most numerous animals on Earth: scientists estimate there are about 10 quintillion insects alive right now (that's a 1 followed by 19 zeros).

All insects share the same basic body plan. Their bodies divide into three sections: the head (with eyes and antennae), the thorax (the middle part where the legs attach), and the abdomen (the back section). Most insects hatch from eggs and transform dramatically as they grow. A caterpillar transforms into a butterfly, and a grub becomes a beetle.

Insects play crucial roles in nature. Bees and butterflies pollinate flowers, helping plants reproduce. Ants and beetles break down dead plants and animals, recycling nutrients back into the soil. Many birds, fish, and other animals depend on insects for food.

People sometimes call spiders insects, but spiders actually belong to a different group called arachnids. You can tell them apart by counting legs: spiders have eight legs, while insects always have six.