Water Striders Can't Skate on Pollution

Water Strider You have probably seen water striders before whether you were aware of it or not. These are the insects you see on the surface of ponds or lakes that effortlessly "skate" along the water. Water striders are predatory insects that can nab their prey the go!

Water striders use the surface tension of water in order to skate on its surface. Water striders are able to evenly distribute their miniscule weight on their lengthy legs that do not break the surface tension of water. But what would happen if water striders were not given pure water to skate on?

Activity: Find out how mixing solutions in water can prove disastrous for water striders!
Materials:
One Penny
One Cup
One Eyedropper
Water
Dish Soap
Procedure:
  1. First, take a guess on how many water drops will fit on a penny (before it starts spilling off). Write your hypothesis down.

  2. Put the water in your cup. One by one count every drop that you put on the penny. Whoa! What are you noticing? What shape is the water forming on the penny? What do you think this proves about water surface tension?

  3. Compare your hypothesis to your results. Are you surprised?

  4. Now dry off your penny. Mix some soap water and pour it in your cup. Make a hypothesis about how many soap water drops you think will fit on a penny and write it down.

  5. One by one count every soap water drop that fits on your penny. What are you noticing? How is this different than the water without soap? Was your hypothesis close?
Now what do you think would happen if a water strider was made to skate on soap water? You guessed it- it would drown. Many ecologists are concerned about pollutants from fertilizers, pesticides, or factories that wash into springs or lakes. These pollutants are hazardous to not only water striders, which are so dependent on surface tension, but to all animals that come into contact with the polluted water.

Water striders are not endangered (although some water strider species are seriously threatened) but there are many insects that are endangered due to human causes. Many entomologists and ecologists are working together to help fix this problem.