- Outdoor temperature between 55 and 100 degrees Fahrenheit (during an evening is ideal)
- Access to an outdoor area with crickets, or purchase crickets from a pet store. If you purchase crickets, make sure they are adults.
- Outdoor thermometer
- Piece of scratch paper and pencil or pen
- When it is between 55 and 100 degrees Fahrenheit outside (and keeping in mind that evenings are usually best for hearing crickets chirping), go to the area with crickets. Make sure you hear some chirping. Alternatively, if you purchase crickets, set them outside in a cage in the shade that allows the outside air to easily reach them. Wait until you hear chirping.
- Have a thermometer set up so that it is measuring the outdoor temperature in the area.
- Pick out the chirping sound of a single cricket.
- Count how many chirps the cricket makes in 14 seconds. How many chirps did the cricket make?
- Write this number down.
- Do this two more times, counting how many chirps the cricket makes in two more 14-second intervals. Write these numbers down. How close were the numbers to each other?
- Average the number of chirps the cricket made in the 14-second intervals.
- Add 40 to the average number of chirps the cricket made in 14 seconds. This equation (which is one of the oldest and easiest-to-use cricket thermometer equations, and is published in the Farmers' Almanac) should give you the approximate temperature in degrees Fahrenheit. According to the cricket, what is the temperature?
- Check the temperature on the outdoor thermometer. How close is the temperature based on the cricket chirping to the temperature based on the thermometer? If they are different, by how much are they different? Why do you think they might be different?
As far back as the late 1800s, there have been articles published noting that a cricket's chirping rate (or number of chirps per second that it makes) changes based on the outdoor temperature. There have been many equations published describing the relationship between the number of chirps per second and the temperature. These equations all vary slightly, depending upon the species of cricket. Using this activity, you may have found that the cricket was within about five degrees Fahrenheit of the temperature measured using the outdoor thermometer, and probably even closer than that. If you did this activity multiple times and found that based on the cricket's chirps it is colder than it is based on the thermometer, this could be because the cricket is farther away from a warm building than the thermometer is, and/or because the cricket is closer to the cold soil. The snowy tree cricket is frequently cited as the most accurate at predicting temperature.
How is a cricket's chirp related to temperature? Crickets, like all living things, have many chemical reactions going on inside their bodies, such as reactions that allow muscles to contract to produce chirping. Insects, including crickets, are cold-blooded and take on the temperature of their surroundings. This affects how quickly these chemical reactions can occur. Specifically, an equation called the Arrhenius equation describes the activation energy, or threshold energy, required to make these reactions occur. As the temperature rises, it becomes easier to reach a certain activation or threshold energy, and chemical reactions, like the ones that allow a cricket to chirp, can occur more rapidly. As the temperature falls, the reactions' rates slow, causing the chirping to also slow.
How do crickets make their distinctive chirp? They do this through a process called stridulation, where special body parts are rubbed together to make a noise. Generally only male crickets make noises. There is a special structure on the top of their wings, called a scraper. Crickets raise their wings to a 45-degree angle and draw the scraper of one wing across wrinkles on the underside of the other wing, called a file. It is somewhat like running your finger along the teeth of a comb.
- To see how accurate it is to use a cricket to tell the temperature in general, repeat this activity when it is different temperatures outside (but still between 55 and 100 degrees Fahrenheit). How accurate is the cricket at telling the temperature when it is warmer or colder outside? How accurate does it seem overall?
- Based on the Farmers' Almanac, you can use a cricket to tell the temperature in degrees Celsius by counting the number of chirps in 25 seconds, dividing this number by 3, and then adding 4. According to the cricket, what is the temperature in degrees Celsius? How accurate is this?
- For an advanced challenge, compare which equation gives the best fit with your calculated temperature data: The linear Farmers' Almanac equations (used in this activity) or the Arrhenius equation, which contains an exponential factor. Information on the Arrhenius equation can be found in the related project idea linked below. Which equation is most accurate?
- Compare the chirps of different species of crickets, or different insects altogether, such as katydids. Which makes the best "insect thermometer"?
If learning about insects and animals appeals to you, you may want to consider a career as a zoologist or wildlife biologist.
For a printable version of this activity visit Science Buddies.For more insect-related fun, try making a bug vacuum.