How to Make a Fly Trap

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  • 2 liter plastic soda bottles (have students bring these to class)
  • Heavy scissors
  • 24" lengths of string
  • Hole punch
  • Bait: Raw meat soaked in a small amount of water (or old beer); old piece of fruit, like ripe banana
  • Cotton ball

Making the Fly Trap
(For student participation, have all elements prepared for assembly–depending on abilities)

  1. Using 2 liter plastic soda bottles, remove label and rinse out with water.
  2. With heavy scissors separate the top of the bottle from the bottom (see diagram). The cut may need to be started with a razor blade or knife.
  3. Invert the top into the bottom part of the bottle.
  4. On opposite sides of the container, punch holes using a hole punch.
  5. Lace 24" of string through the holes and tie with a secure knot to create a hanger, or use string with paper clips attached to each end if students are not ready to tie the string.

Trapping Flies

  • To add the bait, slide the top up the string and drop in bait. If your bait is runny, place a piece of paper (or wire screen) under the bait so that insects do not drown.
  • Set trap in a tree so that rodents (or children) will not be enticed. To protect the flies from heat stress, place the trap in a shaded area. Depending on the weather, season, the bait and the amount of time the trap is left outside, the trap may attract other insects. Be watchful for honey bees.

Handling Flies

  • After retrieving the trap, place it in a refrigerator or ice chest (with ice) for one hour until the flies fall to the bottom. Prolonged chilling may kill them. All the insects in the trap will be chilled and not fly away. Work quickly as the insects may recover rapidly. At this time, separate the flies and other insects from the bait and dispose of bait appropriately. You can handle the insects with tweezers being careful not to pinch off wings, legs or squeezing them too hard. Release other insects outside and place flies in observation chamber and leave at room temperature to resume normal activity.
  • After completing the observation and activity, release the flies. If you need to use flies for experiments the next day, place a piece of apple or wet raisins in the container for the adult flies.

Flies are harmless.

Adapted from Wisconsin Bottle Biology Project. For additional information write: Bottle Biology Program, c/o Wisconsin Fast Plants, University of Wisconsin, Dept. of Plant Pathology, 1630 Linden Drive, Madison, WI, 53706.

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Center for Insect Science Education Outreach The University of Arizona
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