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I couldn’t believe my eyes. There, right in front of me, was a small piece of wood eating a green leaf. I looked again. It was still snacking on the leaf. Was I seeing things? Had the hot, tropical sun gotten to me? After all, it was summer in Costa Rica. That's a country in Central America.

I paused, wiping sweat from my eyes. Then I poked the wood with my finger. It stopped. It looked up at me with big, triangular eyes. Surprise! It wasn't a piece of wood at all. It was a mantid, a kind of insect.

The mantid was hanging upside down on a branch. Its wings made it look like a piece of tree bark. Then I noticed something else. The leaf wasn't a leaf at all. The hungry mantid was really eating another insect—a katydid.

By now, all that was left of the katydid was a pair of wings. A few moments later, the wings dropped to the ground. The mantid was done eating.

The mantid folded its long legs. It sat still. Now it looked even more like a piece of wood than when I had first seen it.

I am an entomologist. That's a scientist who studies insects. Insects are invertebrates. Those are animals with no backbones.

That doesn't mean that insects don't have skeletons. They do. A bug wears its skeleton on the outside of its body. That is known as an exoskeleton. The exoskeleton helps protect the bug from injury.

I thought about how I had been fooled by these crafty critters. Then I thought about how the two insects go about trying to trick each other.

Both mantids and katydids are masters of disguise. Katydids are particularly good at it. There are nearly 7,000 known species of katydids. Many look like something they are not. This is called mimicry.

Katydids often look like plants. Many seem to be leaves. Others look like blades of grass. A few resemble plants covered with mold.

All day, the bugs try to stay perfectly still. Because their bodies look like plants, most predators don't bother them.

That suits katydids well. These bugs are herbivores. They eat plants. They would rather hop away than fight a predator. They are even happier when other animals don't see them.

Once the sun sets, katydids stop sitting still. Suddenly, the plant-like creatures come alive. They begin walking, feeding, and singing.

Eyes are of little use at night. Katydids use their excellent sense of smell to find food. Their long antennae scan the air for whiffs of rotten fruits and other treats. Their antennae can also detect danger. For example, a bug might feel the wing beat of a bat that's too close. Bats eat katydids.

Katydids also have good ears. Their ears, however, are not on their heads. They are on the bugs' knees. Those ears can pick up sounds that humans cannot hear.

Sometimes a predator does get too close. Even then, a katydid can fight back. The bug's strong back legs can propel the katydid into the air. That helps it escape danger.

The katydid's jaws can cut through skin. I know. More than one katydid has sliced through my fingers.

There is one predator most katydids do have trouble fighting, though. It is the mantid. There are roughly 1,800 species of mantids.

Mantids are crafty predators. They eat prey most other animals avoid. Stinging wasps, toxic spiders, and spiky caterpillars are all on the mantids' menu. So are katydids.

Like katydids, mantids often look like plants. They wait for prey to walk by. Their eyes help them look in all directions. Mantids can even see behind their heads.

As soon as a mantid spots a katydid, the hunt is on. The mantid begins to move slowly. Inch by inch, it crawls toward its prey.

Finally, the mantid is close enough to attack. It stops. It waits. It doesn't want the katydid to know what's happening.

Quietly, the mantid folds its front legs back. Then it lashes out, grabbing the insect. The mantid hangs on tightly. It holds the katydid away from its body. That way, the katydid cannot bite the mantid.

Then the mantid begins to munch. It starts with a soft spot behind its prey's head. It eats almost everything. The katydid's wings are the only leftovers.

Katydids and mantids are true survivors. They have lived on Earth since the first dinosaurs.

Scientists first thought that mantids and katydids were closely related. Now we know better. In fact, the cockroach is the mantid's closest cousin.

Still, mantids and katydids need each other. I bent over and picked up the pair of leftover katydid wings. I felt a bit sorry for the katydid.

Yet I knew that it had helped a mantid live for another day. Next time, I might find a pair of mantid wings on the ground. That's the way things go in nature.

Article by Piotr Naskrecki. Top-of-page photo by James Robinson/Animals Animals. "Bug Battles" appears on pages 12-17 of our May 2006 issue.

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