House Fly Reaction Time

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life sciences, mathematics






one class period


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You may print this activity
for educational use.


Before their visit, students will learn about ... their abilities to respond (reaction time).

Background Information

If someone throws something at you without telling you, you immediately make a choice: to catch the object or get out of the way. If you catch the object in time, or move and it misses you, your reaction time is quick.

But no matter how fast you are, you're not as quick as a house fly [graphic]. A house fly reacts 12 times faster than a human. A fly's reaction time is about one fiftieth of a second; yours is one fourth. The insect's two large eyes, called compound eyes [definition], are very sensitive to movement. Any tiny motion in its direction, and the fly zips away.

This activity gives your students a closer look at how quickly they react (reaction time).



For each student team:

  • A yardstick.
  • Chart to record reactions.


What's the fastest animal you can think of? Why is it so fast?

What is reaction time? How would you measure the quickness of someone's reactions?


  1. Divide your class into teams with three students in each team.
  2. Have Student 1 extend a hand with the thumb and forefinger separated.
  3. Have Student 2 hold a yardstick at one end so that the other end of the stick is between Student 1's thumb and forefinger.
  4. Have Student 1 watch the bottom end of the stick and when ready tell Student 2 to release the top end. Student 1 tries to catch the stick between the thumb and forefinger.
  5. The distance that the stick falls before it's caught gives a measure of the reaction time.
  6. Have Student 3 record the distance the stick drops before being caught.
  7. Repeat the procedure a couple of times.
  8. Have the three students switch roles.


Who was the fastest in each group? What does that say about reaction time?

Did any of the students get faster after they tried a couple of times to grab the stick?

What does that say about reaction time?

Adapted from

Abruscato, Joe and Jack Hassard. The Whole Cosmos. Santa Monica, CA: Goodyear Publishing Co., 1977.

Additional Sources

Mound, Laurence. Insect. Eyewitness Books, New York: Alfred A. Knopf, 1990.

O'Toole, Christopher. Alien Empire. 1st ed., New York: Harper Collins, 1995.