by Mary Hoff
When is a stick not a stick? When it's an inchworm caterpillar. This little larva looks just like a twig. If a predator comes to call, the inchworm stands up on one end. Even the most sharp-eyed bird would have a hard time telling it from a real twig.
Many Minnesota animals and plants play tricks on each other. They look or act like something other than what they really are. Unlike human April Fools' tricks, which are just for fun, these tricks are serious business. They help these tricksters stay alive and pass life on to a new generation.
Can you find the treefrogs in this picture? If you look hard enough you can. But if you were a snake searching for food, you might miss them. That's because the frogs are camouflaged--colored so that they blend into their surroundings.
Many Minnesota animals use camouflage to help them hide from predators or sneak up on prey. For example, mottled brown or gray fur coats make deer, wolves, rabbits, mice, and other mammals hard to see against dry leaves, bark, and grass. Birds, especially females, often have earth-tone feathers, which allow them to sit on their nests without catching the eye of a hungry predator.
To hide from fish in search of food, some little wormlike creatures called caddisfly larvae build a shell to cover their juicy little bodies with twigs, sand, or gravel on the bottom of the streams where they live. When disguised, they are hard to tell apart from other bits and pieces of stuff there.
White underwing moths, found in the forests of northern Minnesota, are black and white and gray. That might not seem like a good disguise in a brown and green world. But it is for these moths. That's because they spend their time on paper birch trees. Up against the white birch bark, the moths can hardly be seen.
The underwing moth is an example of a camouflaged insect with a second line of defense called flash coloration. If a predator disturbs the moth, it flashes brightly patterned hind wings and flies off. The predator focuses on the hind wings as the target of its chase. When the moth lands and again hides its hind wings, the befuddled foe is tricked into concluding that the moth has simply vanished.
Other Minnesota critters trick potential predators by mimicking--looking or acting like--things that aren't good to eat.
When its wings are at rest, the tufted bird-dropping moth looks a lot like--guess what? Some members of the leaf beetle family use a similar trick. They look like the tiny droppings of caterpillars.
One species of flower fly looks like a honeybee. Another looks like a hornet. Yet another looks like a yellowjacket wasp. These pretenders even buzz! But they don't sting. Still, would-be enemies stay away because they can't tell the difference between the pretenders and the real thing.
The viceroy butterfly looks almost exactly like a monarch butterfly. How does this protect it? The first time a young bird tries to eat a monarch, it gets an unpleasant surprise. Monarchs taste awful, due to chemicals in the milkweed plants they eat. That bad taste convinces the bird to avoid monarchs--or anything that resembles monarchs, including the viceroy.
When a predator pesters an opossum, this cat-sized mammal tries to flee. But if the opossum can't get away, it might play dead by rolling over, sticking out its tongue, and shutting its eyes. Drool oozes from its mouth. Sound like something good to eat? Not as good as a living, breathing meal. If the opossum is lucky, the enemy will think it is dead and just leave it alone.
When threatened, a hognose snake tries to slither away. If that doesn't work, it hides its head. If that doesn't work, it puffs itself up big and hisses. If that doesn't scare away the enemy, the hognose pretends to die--it throws up, rolls over on its back, oozes blood and feces, and sticks out its tongue. When the threat finally leaves, the snake rolls right side up and crawls away.
Sometimes foolers get fooled. A hognose snake will eat a skink--if it can get a hold of one. About as long as a pencil, this lizard hides under rocks, sticks, and leaf litter. If a snake spies the skink and grabs its long tail, it gets a big surprise: As the skink runs away, its tail breaks off.
Baby skinks have bright blue tails. How do you suppose that helps them survive?
The killdeer knows how to act. If an enemy comes by while the killdeer sits on its nest on the ground, the bird scurries away, dragging its wing as if wounded. Thinking an injured bird is easy to catch, the predator ignores the nest and follows the bird. After the killdeer moves far away from the nest, it flies off, and the attacker ends up empty-pawed.
Not all the fooling that goes on in nature is used to avoid becoming a meal. Some Minnesota plants and animals use tricks to trap a meal.
The pitcher-plant grows in bogs, where the soil lacks the nitrogen plants need to grow. To get a nitrogen-rich meal, the pitcher-plant gives off a sweet smell. When an insect enters the quot;pitcher" in search of a sweet treat, it falls into a puddle of rainwater in the bottom of the pitcher. After the insect drowns, the plant takes up the nitrogen released by its dissolving body.
Design a clever critter to live in your neighborhood. What tricks could it play to survive? Maybe your trickster uses camouflage, mimics something in its surroundings, or acts in a way to scare or attract animals.
Draw or write down your ideas, then share them with your friends and with us. Send them to Letters, Minnesota Conservation Volunteer, 500 Lafayette Road, MN 55155-4046. Or send e-mail to email@example.com.
Mary Hoff, Stillwater, is a science writer and production coordinator for the Volunteer.
A complete copy of the article can be found in the March-April 2000 issue of Minnesota Conservation Volunteer, available at Minnesota public libraries.