Kelly Dorgan

kelly.dorgan at berkeley.edu

Worms in Jell-O

Set-up for worm burrowing demonstration:

Fill a glass aquarium with double strength gelatin mixed with seawater. If you buy the gelatin in bulk, the recipe is 28.35g/L seawater. It is important to use a glass aquarium rather than plastic because plastic is birefringent and will show stress that will mask any stresses in the gelatin. It is also important to boil ALL of the seawater to kill bacteria.

You can buy linear polarizers from Polarization.com . Cut two squares of polarizing film to fit your aquarium and line them up on either side of the aquarium so the polarizers are crossed (and appear dark). Set up a light on one side and observe on the other.

Large worms work well because they are less fragile and the stress fields are larger and easier to see. I recommend using large Nereids. To get the worm to burrow, you need to make a crack on the surface of the gelatin and push the worm down into the crack. I recommend making the crack perpendicular to the polarizing film so you can see the stress when the worm pushes on the crack wall.

Here is the handout I gave to students.

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