Sponsored by the John’s Hopkins Center for Talented Youth, April 14, 2012
Strategies to Escape Ending up on a Dinner Plate
How do living things avoid getting eaten? One way critters can escape predators is to hide by blending in with their surroundings, a strategy called camouflage. For example, if a butterfly is black and rests on a black tree trunk, then it will be able to hide better than if the butterfly is white. If a bird with a taste for delicious butterflies came along, it would have a much easier time finding the white butterfly than the black butterfly.
Camo Relay Race
To demonstrate how butterflies use camouflage to escape predation we played a game.
For this game, we spread a mixture of hundreds of white and black paper butterflies over either white or black construction paper sheets. Each team was given a set of tweezers and a plastic cup. One by one, each team member had to run towards the table where the butterflies laid and, using their tweezers, pick three butterflies as fast as possible, then run back and hand the cup and tweezers to the next person. The game ended after 5 minutes and each team was asked to count the total number of butterflies picked, and the proportion of white and black butterflies in the cup. After writing the numbers on the board, we discussed the results as a group, allowing the kids and parents to make the connection between the color of most of the butterflies the team picked, and the color of their background. What do you think they found?
After the camouflage relay race, we showed the kids and parents pictures of the famous case of industrial melanism in the Peppered moth and explained that this is a real life example of evolution.
A real Life Example of evolution: Industrial Melanism
In the case of industrial melanism, smog from factories during the Industrial Revolution killed the white lichen on the trees, turning them from white to almost black. Before then, the white lichen on the trees gave the bark a white appearance and the white Peppered moths were able to escape getting eaten by camouflaging on them. When the trees darkened because of the pollution, the white moths became easy targets for predators and the few lucky black moths in the population suddenly had an advantage because they were now able to hide on the black trees. These black moths survived to have more black babies, and their black babies had black babies, and so on, until pretty soon the population of moths evolved to become black!
I Spy a Butterfly
To illustrate how well camouflage works as a way to hide from predators, we played an “I spy” game in which the kids were shown an image of a nature scene and asked to find the well-hidden butterfly or insect. When the kids thought they could see the insect they raised their hand and the first one to do so came to the front and pointed out to the rest of the group where the hidden insect was in the image. To see if they were correct, we then removed the background so everyone could plainly see the insect and where it had been hiding.
Hide and Freak
Camouflage is not the only way that animals are able to escape getting eaten. Another way that an animal can escape predation is by startling the predator. In this case, an insect with a drab appearance looks like a non-threatening meal to the predator. However, when the predator comes along, the insect opens its wings and reveals a startling coloration or pattern that causes the predator to hesitate long enough for the insect to fly away. This is called a startle response.
Insects also use color to warn predators that they are poisonous. For example, the Monarch butterfly extracts toxins from its food when it is a caterpillar and it stores these toxins in its body. A predator that eats a poisonous monarch gets sick and spits out the butterfly. Eventually, the predator learns to avoid brightly colored insects because they might be poisonous. This is called warning coloration. “Might be poisonous” is an important concept here because some insects are brightly colored but are not poisonous. These insects trick the predator into thinking they are the poisonous type so the predator won’t eat them. This is called mimicry. One of the most famous examples of mimicry is the case of the monarch and the viceroy. Monarchs are poisonous and so the Viceroy mimics the Monarch in order to scare off predators. For a long time, scientists thought that the Viceroy was not poisonous and so it tricked predators into not eating it by looking like the Monarch. This type of mimicry is called Batesian Mimicry. Recently, however, scientists have found evidence that the Viceroy may actually be poisonous too. Therefore, it may be the case that the Monarch and Viceroy mimic each other in order to send a clear message to predators: Orange and black coloration=poisonous! This type of mimicry is called Mullerian Mimicry.
To show the kids examples of all the types of strategies insects use to avoid getting eaten, we showed them specimens of real insects from the Yale Peabody Museum.