Meal worm experiment puzzle with sample solutions

Some experimenters wanted to test the response of meal worms to light and moisture.  To do this they set up four boxes, as shown in the sketch below.  They used lamps for light sources and constantly watered pieces of paper in the boxes for moisture.  In the center of each box they placed 20 meal worms.  One day later they located and counted the number of meal worms at the different locations in the boxes. They found the meal worms had crawled to the different locations in the boxes and recorded the results as below:

mealworm image

The diagrams show that meal worms respond to (respond means move toward or away from):

  1. Light but not moisture
  2. Moisture but not light
  3. Both light and moisture
  4. Neither light nor moisture

Explain your choice.

Student sample answers: Names are fictitcious

Juan Diego

“No definite pattern was followed by the meal worms.”

Norma Kuhn

“Because even though the light was moved in different places, the meal worms didn't do the same things.

Colleen Wiz

“They usually went to the end of the  box with the light.”

Jackie Haun

“Because there are 17 worms by the light and there are only 3 by the moisture.”

Harold O’Kelly

“Because in all situations, the majority go where there’s light. Wetness doesn't seem to make a difference.”

Barbara Danour

      “Boxes I and II show they prefer dry and light to wet and dark, Box IV eliminates dryness as a factor, so they do respond to light only.  Box III shows that wetness cancels the effect of the light, so it seems they prefer dry.  (It would be clearer if one of the boxes was wet-dry with no light).”

David Kentin

“ When the light was on the dry side they all crowded to the dry side.  When it was on  the wet side, an equal amount went to each side.”

Alexa Johnson

“In experiment 3 the meal worms split half wet, half dry.  So it’s safe to assume that light was not the only factor involved.”

Deloris Bates

“I, II, and IV show that meal worms seem to like the light, but in III they seem to be equally spaced. This leads one to believe that meal worms like the dryness and the reason in pictures III and IV they are by the light is because of the heat that the light produces which gives a dryness effect.”

John Blake

“The Meal worms in all cases respond to light.  However in box 3 the division is about 1:1.  This shows that the worms are attracted to the light but not like the situations where the dry area was next to the light.  When there is no choice between wet and dry such as in case IV the worms turn to the light.” They might also test a box like this wet/dry with no light to further verify the effect of moisture.

Or create a matrix:

  Wet Dry Totals
Most light 10 + 15 = 25 17 + 18 = 35 60
Less light 3 + 4 = 7 10 + 2 = 12 19
Totals 32 47  


  Wet Dry Totals
Most light      
Less light      
No light      

Could also add a third to moisture. Wet, moist, dry (moist = 1/2 of what they set it to be) .