Cricket behavior: observing insects to learn about science & scientific inquiry.
Students have probably already informally observed some behavior of the patterns of crickets and they may have already wondered about the romantic sounds they make during the night. Although they may have listened to crickets, they probably have never actually watched them "sing." In the classroom, where these insects can be conveniently observed, students can take time to carefully notice in new ways how crickets behave. I have found that students will delight in the surprising minute details of how these little animals move and interact with each other. Small changes in postures, appendage movements, song variations, feeding behavior, range of movements, and interactions between individual crickets begin to complicate what students think they know. Soon, discussions include intellectual attempts to relate what they see and hear to broader evolutionary and ecological questions. Students can learn to test ideas and ways to conceptualize why these creatures might behave the way they do. Through these processes, students learn not only a lot about these particular insects but they also learn about scientific reasoning and habits of mind as they practice original scientific inquiry as described in the National Standards (American Association for the Advancement of Science, 1993; National Research Council, 1996). These propensities, attitudes, actions, and the related scientific habits of mind that are involved in designing and carrying out original experiments are too often lacking in American classrooms. However, the lessons learned are vital to scientific literacy as described in the National Standards.
The cricket behavior investigations and experiments explained here are adaptations of classic experiments that I used every fall to introduce my students to biology (adapted originally from Alexander, 1961). Please also see Dingle (1975a,1975b) as well as the recent work of Cade and Cade (2007) and articles published in this journal (i.e., Whiteley et al., 2007). They require very little equipment and can be used in any school setting from grades 5-12. Although this study takes no sophisticated equipment, it does take some imagination, ingenuity, and class time. In the beginning, it takes several class sessions to set up the original experiments and model the kinds of inquiry students later do independently. After the original class sessions, students need several 10-15 minute observation sessions and at least one whole class session (for debriefing and discussion) per week during these activities. I found that the relatively large, common black crickets of the genus Gryllus work well because they are active, relatively large, quite territorial, and display easily-observed social behaviors. Although it is far better to use wild-caught crickets, I have also used Acheta domesticus, the brown cricket available at pet stores and bait shops. These common crickets are much less aggressive and their behavior is less dramatic. More importantly, they probably have been held in large cultures for extended periods of time and will not likely display wild-type behaviors. I have also used Nemobius crickets but I found them less desirable because of their smaller size. Dingle (1975) suggests that other cricket species will work and will provide interesting comparative studies. Have your students visit the Ohio State University Extension site at http://ohioline.osu.edu/hyg-fact/2000/2066.html or the Featured Creatures site of the University of Florida http://creatures.ifas.ufl.edu/misc/crickets for the natural history, identification, and information about which species they might find in your area of the country.
In addition to the investigations and experiments described here, my students have also designed and carried out experiments that relate to reproductive potential, food preference, and song frequency, as well as other topics that pique their interest. These extensions address learning goals and objectives often left out of our classroom instruction such as: writing hypotheses, designing experiments, setting up controls, deciding how to collect qualitative and quantitative data, organizing and analyzing data, deciding what counts as evidence, making conclusions, and reporting experimental results. I have found that discussing their ideas for experiments also provides students with many opportunities to discuss the ethical issues related to the treatment of living things in laboratories and in the wild. Students invariably agree that school experiments should never be hazardous to animals in any way and I have very seldom had to deal with cricket abuse.
Crickets, like other insects, have many reasons for moving about, including foraging for food, competing for space, searching for a mate, avoiding parasites, and escaping predators. The world is a dangerous place for small creatures and although moving about is beneficial and necessary for survival, it is always very risky and costly. Predators such as birds, snakes, and other insects are adapted to key into this movement and the sounds it produces. Although many are caught and eaten, a critical percentage of crickets in a population must eat, grow, and reproduce in order for the species to be successful. The individuals successful in avoiding predators and parasites, while participating in the sexual selection process, make a contribution to the gene pool and future generations (i.e., Sugden, 2006; Fedorka & Zuk, 2005; Simmons, Zuk & Rotenberry 2005; Tregenza, Simmons, Wedell & Zuk, 2006) while those who are not make an immediate contribution to the food chain.
A conceptual device scientists can use to understand cricket movement behaviors is the Optimal Foraging Theory. Scientists use this theory to help them think about the cost-benefit ratio associated with the behavior of prey species (Abrahams Carter, 2000; Dawkins, 1995; Lima & Dill, 1990; McCleery, 1978; Stephans & Krebs, 1986). According to this theory, animal decisions about the risks of predation are assumed to represent a balance between costs and benefits of the related behaviors. For example, prey species seem to balance different stimuli and responses to take advantage of any cover or shelter. Recent studies support this reasoning and have suggested that the risk of exposure and predation can influence an animal's behavior when foraging for food or engaging in reproductive behavior (Abrahams Carter, 2000; Wellborn, 2000). Cricket survival behaviors that are related to shelter, nutrition, and reproduction compete with each other and with the need for cover and safety.
Another cricket behavior, "singing," also illustrates the relationship between costs and benefits. Cricket singing is beneficial in courtship but, like moving about, it is also very costly because it takes energy and potentially exposes the individual to predators and parasites. This makes singing interesting to scientists, and recent studies have suggested that cricket song is species specific (Gray, 2007) and that behavior changes, evolves, or adapts as a result of age (Jacot et al., 2007), size and hunger (Nosil, 2002), aggression (Brown et al., 2007; Hofmann & Schildberger, 2001; Hurd, 2006), temperature (Martin et al., 2000), and the behavior of parasitic wasps (Gray et al., 2007; Sugden, 2006).
In addition to asking questions about cricket songs and cost/benefit relationships, scientists also study social behavior of crickets. For example, crickets exhibit agonistic behavior as individuals compete with each other for space, food, and opportunities to mate and reproduce. The associated behaviors might represent a rather complex social organization called dominance hierarchy or even territoriality (Dingle, 1975a, 1975b). Dominance hierarchies can be simple in that one animal is dominant over another or they can be linear like a pecking order in chickens. Careful observations under controlled conditions can help scientists decide which kind of behaviors are exhibited. Territoriality that defends a personal space is related to dominance in that an animal might be more aggressive, not necessarily bigger or stronger, than another individual near its own physical marker, shelter stone, or burrow. The same animal venturing into the other individual's territory might now reverse roles and retreat from the defender of that space. In this way, dominance might depend on the defended territory in which an encounter takes place.
[FIGURE 1 OMITTED]
If we place a cricket in a new environment like a classroom arena, it will look for shelter and structure and limit its time away from such cover. To minimize movement and exposure, it might spend its time near relative safety and as close as possible to available food. Especially if cover is limited, it might even defend this space from other crickets. If an individual defends this space against others of its own species, the action is called territorial behavior and the defended space is called a territory. Each territory will have a boundary or limit beyond which the individual will not defend. The boundary might or might not be directly apparent to the human observer. The boundaries might coincide with physical markers or they might be marked chemically and therefore be invisible.
In discussing these things, students might also wonder if females and males, large and small, young and old, hungry or satisfied crickets behave differently. Also, saying that these insects "seek," "look for," or "defend" these places fits the criteria of good hypotheses since these statements explain something observed and also predict what will happen if crickets are observed on other occasions. This kind of questioning and reasoning naturally leads to discussions about anthropomorphism and why scientists try to avoid it. Students should look up and discuss the scientific meanings (versus common or colloquial meanings) and uses of terms like territory, dominant, agonistic, and aggression.
This simple behavior study can be done in a typical school classroom with very inexpensive and readily-available materials. You can find most of these materials at your local hardware or building supply store. The study involves placing several black crickets, male and female, into a test arena, controlling for variables, and observing their behaviors. The size of the arena is important only in that it should be large enough to give the crickets freedom of movement and to find their personal space. Although a glass 10-gallon aquarium works fairly well, it is somewhat small. I constructed an arena out of clear plastic (Plexiglass[R]) and a glue specifically made for it. Making my own arena allowed shorter (15 cm) side walls that the crickets were not able to climb or jump over and yet were short enough for easy observation (see Figure 1). A clear cover helped maintain moisture and kept the crickets from escaping. The arena cover should have drilled holes to give adequate ventilation. Students can easily draw a grid on the cover with a permanent marker that will help in recording data. The plastic must be clear because students need to look through the walls or cover of the arena to make their observations. If your classroom is relatively humid, you might be able to eliminate the cover of the arena and thus make close observation easier. Place the arena on a table that is low enough that students can comfortably see inside for extended periods of time. The arena should have a couple inches of moist, but not wet, sand in the bottom, deep enough for the female to insert her ovipositor and lay eggs. Play sand available at your local hardware store works well. Small physical markers like stones, sticks, or other objects should be placed in the arena. Small matchboxes or small earthenware pot trays with a small section of the rim chipped away work well as shelters. You can purchase cricket food from pet shops, biological supply houses, or feed them a mixture of oatmeal, cracked corn, and other seeds. They also live well eating dry cat or dog food. Water can be supplied with a small alcohol burner or film canister fitted with a wick, filled with water, and turned on its side so that the wick stays wet. An occasional slice of apple or pear can also be used to supply moisture if they are replaced often to prevent mold. Crickets can be marked by placing a small colored dot on their thorax using a permanent marker with a fine point. Leave plenty of foraging space and do not overcrowd the arena. When the experiment is carried out, the lights should be dimmed, and students should be quiet. They should stand or sit close enough to see, but far enough away that they do not disturb the crickets.
* 12 or more male and female crickets
* observation arena equipped as described above
* small plastic containers with covers to isolate crickets. Cover the bottom of the container with sand and provide shelter, water, and food.
* small alcohol burners or plastic film canisters with wicks for supplying moisture
* suitable cricket food (see above)
* stopwatch or clock with second hand
* tape recorder with external microphone for taping cricket sounds and playing them back
Be sure to introduce this experiment by discussing predator-prey relation ships, the niches of different kinds of insects, and the behaviors of various insect predators and parasites. Remind students that a high population of a species of insect at the bottom of the food chain supports the nutritional needs of a large variety of other creatures. Students can also reason that it is beneficial that the reproductive behavior of an insect species selects for the most fit individuals to reproduce and contribute to the gene pool. Perhaps discuss how human trophy hunting might cull a deer herd in a very different way by selecting for the strongest and best specimens in a population. Brainstorm the concepts of optimal strategies and stimulus response, as well as specific examples.
Do not discuss agonistic or territorial behavior with your students before they begin their experiments. Instead, ask them to tell stories of cricket sightings. Students might also tell folklore stories about song frequency and other behaviors. You will need to decide if it is best to discuss optimal foraging theory before or after the experiment. Discussing it before the experiment gives students a framework for reference and a theory to test. On the other hand, it might seem like giving away some of "the answers" or giving the impression that scientists set out to prove theories, a common misconception among many people. Either way, students should be able to explain how animals, when foraging for food, need to find it efficiently. Energy expended obtaining food must be less than energy gained from the food while at the same time, minimizing the risk of exposure to predators. Ask students if they think these behaviors are learned or inherited and what evidence they have for their decision.
After this discussion, students should be able to help design this study and develop their own specific procedures and experiments. Discuss why it is important to control for variables such as sex, age, health, scents in the test arena, and presence or absence of food. Also discuss why it is important to conduct several trials with different crickets. Students should work in small groups designating a timer, recorder, and cricket handler (a small aquarium fish net works as a capturing device). Other students can take observations that correspond to timed intervals. Discuss why it is important, in any scientific experiment, to make as many observations as possible (see Table 1). As students often do not know how to observe closely, you will probably have to help them record their first observations and teach them the differences between observations, inferences, and conclusions. Discuss the need for a control in any experiment and consider establishing a different arena with a control group of animals. Students should record cricket songs whenever they can and label the different recordings according to situation. They can use a simple tape recorder with external microphone to tape their own crickets. They could also download cricket songs from the Featured Creatures site of the University of Florida (http://creatures.ifas.ufl.edu/misc/crickets). However, if they download songs, they should discuss the different variables this introduces to the investigation. For example, the recorded crickets might be of a different species or live in different geographic locations. Discuss possible ways to use checklists and data tables to record cricket positions, postures, and orientations at timed intervals for repeated trials (see Table 2).
Crickets--A New Space--Observing First Encounters
Some of the most interesting cricket behaviors happen when crickets find themselves in a new space and in the presence of others that they have never encountered. For this first experiment, prepare the testing arena with moist sand but do not provide food, shelter, or water.
1. Using small plastic containers, isolate four to five marked male crickets from each other for at least 24 hours.
2. After the isolation period, place all of these crickets in the test arena and immediately begin taking observations. When the designated timer calls "time" (every 30 seconds), the recorder marks the individual position on the grid (Table 2), using an arrow to note the direction the cricket is facing at the time, and consecutive numbers that correspond to timed intervals. Participants should record observations as they wait between time intervals. Pay special attention to times animals come in contact with each other (see Table 1). Look for subtle as well as not so subtle behaviors: antenna movement and positioning, stance, orientation, etc. Although the more time intervals the better, a 15-minute testing time should be sufficient for this first experiment.
3. Establish a classification scheme for observed behaviors. Be sure students record body movement, posture, antennae movement, and cricket sounds as crickets interact.
4. Dingle (1975a,b) and Alexander (1961) suggest that encounters vary in intensity depending on certain observable behaviors. Dingle and Alexander also record "win and loss" tallies for individuals. Have groups discuss the encounters they observe and if they should classify their cricket behaviors in the same way that Dingle and Alexander did. What evidence do they have that suggests that the observed behavior is agonistic? What evidence do they have that there are "winners and losers?" Are these descriptions appropriate for insect encounters?
5. Discuss if there is a dominance hierarchy among these crickets and how long it took to establish it. What evidence do groups have for their assertions? Is the hierarchy simply linear or is it more complex than that? Where on the hierarchy does each cricket belong?
6. Discuss and test other variables in which student groups are interested. For example, repeat the experiment with females only, with females and males, with same-age or mixed-age crickets. Does size of antennae or other physical characteristics make a difference? Remember to discuss the need for evidence in any tentative claims. Discuss with the class what constitutes evidence in each case.
[TABLE 2 OMITTED]
Territoriality And/Or Personal Space
Perform Steps 1-5 (above) when animals first encounter each other. The following set of investigations is designed to test other variables associated with cricket behavior. Before beginning, place food and water into the arena.
1. Place five or six marked male crickets and the same number of shelters into the arena. Place some physical markers such as small stones, sticks, and other small objects into the arena. These markers should be chosen carefully so that crickets can't use them as shelters. For a period of one week, record observations and discuss any data that can serve as evidence for personal space or territoriality. What behaviors classified in the previous section are observed during the week of acclimation? Where do encounters take place? Do you observe any different behaviors? Modify your behavior classifications according to what you see.
2. Place another marked male cricket (but not another shelter) into the arena. Observe any interactions and record any behaviors of the crickets. If you tentatively found a dominance hierarchy in the previous section, be sure to keep these findings in mind.
3. Repeat using different crickets representing different positions on the hierarchy.
4. Discuss the nature of the encounters and their relationship to space and hierarchy assertions.
5. Write hypotheses about your crickets' behaviors and design other experiments to test your hypotheses. Try to test only one variable at a time and control for confounding variables carefully.
Sexual Behavior in Crickets
In the previous sections, you tested for cricket behaviors that were related to space, aggression, and territory. Although you may have already observed some male/female interactions, in the following section we will focus on these sexual behaviors. Before starting, isolate males from the females for several days. Record cricket songs whenever you can and label the different recordings according to situation.
1. Place a marked male cricket into the test arena, let him acclimate for a short time and then add a female. Record the behaviors during the initial encounter and further encounters over time. Repeat this experiment but vary the order by placing the female into the arena first and then adding the male. Repeat with different males and females. Do individual dominance and hierarchy positions seem related to what you observe?
2. Place one female into the arena and add two males. Observe what happens. Repeat with different marked males from the previous two sections.
3. During each of the encounters, be sure to record behaviors, sounds, and sequences in behaviors. Discuss how song, frequency of sounds, and other behaviors seem to be related to sex.
4. Introduce a female into an arena with a group of males (as in the Territoriality experiment) who have established personal space and are defending territories. How does the cricket behavior change? Which males are successful in mating with the female? Does the presence of a receptive female have any effect on the dominance hierarchy and territoriality?
Nature & Function of Song
In the previous three experiments, you may have wondered if cricket songs depend on certain contextual variables. For this last experiment, use the songs you previously recorded. Discuss if students can make inferences about different songs and their purposes. What evidence do they have for their inferences? For discussion, ask if some songs are courtship songs, calling songs, or defensive songs.
1. Play selected songs to different crickets you have intentionally chosen. How does one particular song affect a particular dominant male? A particular female? A group of males?
2. Discuss your results in the three previous experiments and write possible hypotheses that are related to song. Remember that a hypothesis must tentatively explain something observed as well as predict the results of future experimentation. Have students design and carry out experiments to test their hypotheses. For example, does a female's behavior depend on which male the song belongs to? Are males attracted to song? Does the song of a courting male result in different behaviors of a female than a calling song? Be sure to discuss what evidence students have that a particular song has a particular affect. What is it about a song that makes it different? Is it frequency? Rate? Pattern? Other variables? Do your crickets behave differently to pre-recorded songs of different species?
Students should be able to brainstorm other hypotheses to test. In making any changes to the study, make sure students discuss other possible variables that might affect their results.
Assessments of Student Learning
Assessments should always relate closely to the goals and objectives for student learning. As stated above, students will learn about a cricket species specifically, insect behavior, and animal behavior in general. They also should learn about the process of scientific inquiry that includes observing and recording skills, representing data in charts and graphs, the importance of using averages (means), and how to analyze data using mathematics. In addition, other important lessons include: a spirit of inquiry, curiosity, to ask good questions, and to make predictions. Students also gain experience in designing and carrying out their own investigations and experiments; necessary components of a standards-based curriculum. Although there are a variety of creative assessment strategies that could be used, one way to measure student learning is through an individual or group lab report that follows a typical scientific publication format. This includes: introduction, literature review, methods, data analysis, conclusions, and suggestions for further study. For an example of an assessment rubric, see Table 3, "Cricket Behavior Report" below. Have your students organize a cricket behavior conference where individuals or groups of students present their findings either as Power Point' presentations or poster sessions. This could be done during the school day, inviting other students, or it could be organized as an evening event with parents and community members invited.
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Rop, C. (2000). Mouse Behavior: Conjectures about adaptations for survival. The American Biology Teacher, 63(5). 346-350.
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Whiteley, A.R., Woolf, J, Kennedy, K., Oberbillig, D. & Brewer, C. (2007). Crickets in the classroom show how biologists use sampling and mathematics to estimate population size. The American Biology Teacher, 69(5), 292-297.
CHARLES J. ROP, Ph.D, is Associate Professor of Science Education, University of Toledo, Byron Center, MI 49315; e-mail: Charles.Rop@utoledo.edu.
Table 1. Timed cricket observation sample data chart. TIME OBSERVATIONS OF CRICKET BEHAVIOR INTERVAL # SECONDS KEYED TO TIME INTERVAL 1 0-30 2 31-60 3 61-90 (Events should be recorded at the appropriate time interval.) 4 91-120 5 121-150 (Continue the Table for the correct number of time intervals.) Table 3. Cricket Behavior Report: Sample Lab Report Assessment Rubric. In the spaces provided, rate your lab report using X+ for excellent, X for good, and IP for "in process." Be sure to use the comments spaces when you wish to explain something. Use NA for criteria that do not apply SECTION OF REPORT SELF PEER TEACHER EVALUATION EVALUATION EVALUATION Introduction * I included a central research question(s). * I briefly explained how this topic is important to us. * I clearly explained what I did, briefly told what I learned that I didn't know before. Comments Literature Review. I included relevant sources ... * that help me understand my own study. * that helped me see a need for my study. * that helped me with my inquiry methodology. Comments Procedure or methods * I explained what I did and why I did it. * I was especially careful to explain how my methods related to my research questions. Comments Data collected * I included all the data and laboratory notes. * I included observations keyed to time intervals. * My data is displayed in appropriate, readable form. * All charts and diagrams are clearly labeled. Comments Data analysis * I included all charts and graphs of my data. * My charts and graphs help teach my reader. * I labeled all charts and graphs, diagrams and drawings needed to show my reader what the data can tell us. Comments Conclusions * I clearly stated my conclusions. * I explained how the data became evidence for conclusions. * I put findings in the context of other scientific studies. * I made suggestions for further study. Comments Writing performance * I used clear, easy-to- understand language. * I followed all the rules of grammar. * I wrote in complete sentences (except in Data section). * I edited my work and checked my spelling. Comments Overall Rating
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|Title Annotation:||INQUIRY & INVESTIGATION|
|Author:||Rop, Charles J.|
|Publication:||The American Biology Teacher|
|Date:||Apr 1, 2008|
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