Build a Better Moth Trap: Will Different-colored Lights Affect How Many Moths You Catch?
AbstractYou are coming into the house after a game of flashlight tag with your friends, but the front porch light is not on for you to see the doorknob! What is going on? Maybe your parents know that turning a light on means moths will gather there, and they do not want you letting moths inside when you open the door. You have probably noticed how moths are attracted to lights at night. They will even fly dangerously close to flames in their journey toward light. In this project, you will learn a theory about why that is, and investigate whether or not moths are equally attracted to different-colored lights.
David B. Whyte, PhD, Science Buddies
Sabine De Brabandere, PhD, Science Buddies
Determine if moths are equally attracted to different-colored lights.
Moths are not as colorful as butterflies, but they can still make for remarkable pictures and show some intriguing behaviors.
Figure 1. Grass moth (Wikimedia commons user Fir0002).
Many people wonder, at one time or another, why moths fly toward lights at night. Are they searching for something near the light? Or are they, perhaps, looking for a place to get warm? While there is no clear and definitive answer to this question, scientists generally agree that the answer has to do with the moth's use of the Moon to direct its flight, and its confusion when an alternative light source is present. When moths fly at night, they use light from the Moon for navigation. Light from the Moon comes from very far away, so the light reaches both of their eyes with the same brightness. Using this environmental cue from the Moon, a moth can fly in a straight line. If the light is from a closer source, however—such as a lightbulb or a campfire—it is perceived as stronger in one eye than in the other eye. This may cause the moth to turn in its flight path, rather than flying straight. Because it continues to turn as it flies, the moth approaches the light in a spiral path. At some point, the moth actually flies into the light source. Another question you might have is why do the moths tend to settle down near the light source? Some researchers have suggested that, having reached the bright light, the moth is tricked into thinking the Sun is out, and since it is nocturnal, it then settles in to sleep. In this project, you will set up light sources of various colors to determine if and how the color of the light affects the moth's behavior.
Terms and Concepts
- Environmental cue
- Why don't insects fly toward light sources during the day?
- Based on your research, what other kinds of environmental cues do insects and other animals use to help them navigate?
- Can you think of reasons why it would be to the moth's advantage to fly toward a light source? Hint: See the HowStuffWorks, Inc. entry in the Bibliography, below, for some possibilities.
- HowStuffWorks, Inc. (n.d.). Why are moths attracted to light?. Retrieved July 15, 2009.
- Stevensen, A. (2008, October 20). Why are moths attracted to light?. Retrieved July 14, 2009.
- Farly, C. (2011, August 7) The Moth Trap. Retrieved August 3, 2015.
- Butterfly conservation (n.a.) Finding Moths www.mothscount.org. Retrieved August 3, 2015.
Materials and Equipment
- A way to keep track of the moths that come; see the Procedure for suggestions.
- Small table or desk lamps (4); should hold standard screw-in lightbulbs
- Colored lightbulbs, standard size; red (1), green (1), blue (1), and white (4); all available at most large hardware and department stores. Use the same wattage for each color of bulb.
- Extension cord(s); to power lamps, if needed
- Tape measure
- Masking tape
- Permanent marker
- Timer or clock
- Flashlight, so you can see as you make notes
- Lab notebook
- Graph paper
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You will need access to moths with which you can experiment. Doing this project will depend on the seasons, since it involves studying moths around your house. Perform the following steps to make sure you will have enough moths to study.
- Locate outdoor lights near your home that are on at night, such as a porch light.
- Observe whether moths are flying around the light.
- If there are moths, proceed with the rest of the experiment.
Decide How To Count Moths During the Experiment
You will have to figure out the best method for keeping track of the number of moths in each experimental setup. Below are some suggestions to get you started. As you choose your method, we suggest a goal of 30 moths or more so you can make meaningful comparisons, but use your judgement to decide on the right number of moths.
- If you have plenty of moths in your area, you can count the moths continuously for a given interval (like 15 minutes). Put out a white sheet or towel near each setup and count how many moths land on it.
- If you have a high-quality flash camera, you can take pictures of the lightbulbs and nearby moths, and count the number of moths in the picture. Be sure to include the masking tape labels (which you will be making later) in the pictures.
- Moth traps, like the one shown in this video, are a better option in areas where moths are less abundant, as the moth traps can be left out all night.
Setting Up Your Experiment
In the steps below, you will set up your lamps, and possibly white sheets or moth traps. First you will count the number of moths that are attracted to white light at each spot. With white lightbulbs in four of the lamps, you would expect to get similar numbers of moths at each light, right? But what if there is a stronger wind at one spot, or some other reason that the moths do not go to the white lightbulbs equally? The data with the white lightbulbs helps control for this kind of variation that is not due to the color of the lightbulb.
Place the four lamps outdoors at night, as follows:
- Plug them each into a power source.
- Set up the lamps in areas that do not have other strong light sources.
- The lamps should be separated by at least 5 meters (15 feet). You can change the distance they are separated, if you choose, but avoid having one lamp too close to another lamp.
- Label the lamps 1–4, using the masking tape and the permanent marker.
- Make a note in your lab notebook about the location of each lamp. Also make a sketch, showing the position of each lamp.
- Remove the shades from the lamps. Any color in the shades could affect your results.
- Before you plug in your lamps, insert a white lightbulb into each lamp.
If you use white sheets or moth traps for counting, place them near each lamp at an equal distance from and the same orientation to each lamp.
- Measure the distance of the sheets or moth traps from each lamp and record these distances in your lab notebook.
- Make a sketch of how the sheets or moth traps are placed near each lamp.
- Make a table like Table 1. It will help you record your observations.
|Trial 1||Trial 2||Trial 3||Average|
|Only white lights||Light #1|
|Different-colored lights||Light #1 - White|
|Light #2 - Red|
|Light #3 - Blue|
|Light #4 - Green|
The goal here is to count enough moths that you can make meaningful comparisons between the different lamps. Counting at least 30 moths might be a reasonable goal, but use your judgement to decide on the right number of moths. Change the observation time period, as needed, to count a sufficient number of moths, but once you settle on a time period, stick with it and make observations for this duration each time.
- Ensure all lamps have white lightbulbs. If they do not, replace the colored lightbulbs with white lightbulbs.
- When it is dark, turn on the four lamps.
- Make observations:
- Record the date and time at which you start observing.
- Count the number of moths attracted to each light during a specific time period.
- Record the observation time period.
- Record the number of moths counted in your data table for each of the four lamps.
- Turn off the lights and let the lightbulbs cool before replacing three of the white lightbulbs with the other three different-colored lightbulbs. Important: Be sure to unplug the lamps before you change out the lightbulbs.
- Note in your lab notebook which of the original white lights have been replaced with colored lightbulbs. Remember to adjust your data table, if needed.
- For example: Lamp #1 - White, Lamp #2 - Red, Lamp #3 - Blue, and Lamp #4 - Green.
- Make a sketch of the positions of each colored lamp.
- Turn on the lights.
- Repeat step 3.
- Repeat steps 1–7 two more times for a total of three trials. Having several sets of data ensures that your results are accurate and repeatable. Note: Do not change the position of the colored lightbulbs for subsequent trials, since this would add another variable.
Analyzing Your Results
- Graph the data for each trial. Put the number of the lamp and the color of the lightbulb on the x-axis and the number of moths caught on the y-axis.
- Make side-by-side bar charts for all three trials and compare trends.
- Average the data by adding the data for each trial and dividing by three (the number of trials you performed). Record the average in the last column of your data table.
- Graph the averages on another graph.
- Looking at your graphs, can you make any conclusions about whether or not one color appears to attract more moths?
Ask an Expert
- As another control, count near a light that is not turned on. What does this control tell you?
- Repeat the procedure, but put the lights in different locations. Does this change your results?
- Test if heat is attracting the moths, rather than light. To do so, compare incandescent bulbs (they will be warm) with LED bulbs (very low heat output). Choosing colored lightbulbs will help limit the difference in light spectrum emitted by the different light source types.
- Study how a white LED lightbulb compares to a white incandescent lightbulb. This study might not reveal what exactly attracts the moths, as there are several differences between these two light sources (like heat output, light spectrum, etc.). The study is still relevant however, as its outcome can help predict the impact that switching outdoor lighting has on moths.
- Try a black light to determine if moths respond to ultraviolet (UV) light.
- Use the data from the trials with all white lightbulbs to correct for variation not due to color. For each light, divide the number of moths caught with the colored lightbulb by the number of moths caught with the white lightbulb. For example, if light #2 had 30 moths with the white lightbulb and light #2 had 15 moths with the red lightbulb, the ratio would be 15/30 = 0.5. Graph this ratio for each light.
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