Learning in Cockroaches
Lab Purpose:To see, if by providing a positive stimulus, students can detect learning in cockroaches. A secondary purpose is to provide students with the opportunity to carefully observe and work with an insect they normally find offensive. Thus students will develop a keener appreciation of the complexities of experimental design and of animal life.
Description:First students make careful observations of cockroach anatomy and behavior. Due to the reputation of the cockroach, students find them intriguing subjects of study. Assessing the behavior of these insects in a maze, allows students to decide if the cockroach manifests learning or an inability to learn. The strongest piece of this activity is challenging students to design their own controlled experiment which assesses some aspect of cockroach behavior.
Background Notes for the teacher:Classification:
The cockroach species selected for use in this activity is classified as follows:
There are many other varieties with which this type of student investigation could be conducted, but we have chosen Blaberus for several reasons. Its large size makes its immediately attractive, yet repulsive to students. Its life cycle is easy to follow and the seven or eight molts required to reach the adult stage beautifully illustrate insect growth and incomplete metamorphosis. The nymphs require from 140 to 200 days to reach maturity. The adult, if provided with optimum conditions can be expected to live for up to 20 months.
Blaberus is readily available in standard, school science supply catalogs (as the Giant Cockroach) at a reasonable price. It is confined to the American tropics and temperate South America making it unlikely that the organism would be successful in establishing large breeding populations in colder regions of the country. Another important point, Blaberus does not bite and prefers to scurry rather than fly. It does have an adhesive organ between the claws on its feet and can climb smooth surfaces.
The cockroach is a prime candidate for most loathsome, obnoxious, and disgusting insect. The pest status of the cockroach derives mainly from an esthetic abhorrence more than anything else. It is associated with thriving in unclean conditions, rapidly producing large populations, and moving rapidly in an unpredictable manner. These animals have been clocked at a speed of 50 body lengths per second on a treadmill located in the research lab of biologist Roy Ritzmann at Case Western Reserve University. This is the equivalent of Carl Lewis doing the 100-meter in 1.09 seconds! (Kelly, 1994)
The word cockroach is supposedly derived from the Spanish word "cucaracha." One early name was "lucifuga" stemming from its habit of shunning light. Throughout history, tales of the cockroach have been recorded. Rau wrote that, "one often reads of the injury done to the eyebrows of sleeping children by Periplameta americana in Central and South America. The story, incredulous as it may seem, is that roaches at night find sleeping children and feed upon their eyebrows. From my own experience - I was awakened by a tickling sensation on my face only to find upon opening my eyes, a pair of long cockroach antennae playing delicately for sense impressions while the cockroach's extended mouth parts were imbibing moist nourishment from my nostrils." (Rau, 1940)
Cockroaches are ancient insects having existed very successfully, relatively unchanged, for approximately 400 million years. This means that they have inhabited Earth 100 times longer than humans. Fossil cockroaches are found in rock layers dating from the Carboniferous era which is known for high humidity and huge populations of plants. They evolved with the flora, rapidly outnumbering all other groups of winged insects. They have remained relatively unchanged and unspecialized from the Carboniferous to present. Presently there are 3,500 known species, most of which are tropical.
Cockroaches show a great diversity in size and coloration. Many species are diurnal (active in the daytime) while others are nocturnal, some are semi-aquatic, some are wood-boring, and fewer than 1% are house pests. Many of the tropical varieties are omnivorous scavengers. What has attracted some species to human dwellings is the diversity and quantity of food available. Cockroaches are great opportunists with some even being accomplished sailors. According to an old Japanese Navy communication, "a seaman who has captured 300 cockroaches will be granted one day shore leave." (Cornwell, 1968) However, few species are good at tolerating cold temperatures. Today, as in the past, most are found in warm, moist low places with much vegetation.
One feature that makes the cockroach different from its close relatives the locusts and crickets is its lack of a visible ovipositor (egg depositor). Through time it has become smaller in size and is not visible externally. Its function, in many species, is to guide eggs into an abdominal cavity in the female where eggs are held and incubated internally until hatching. It is thought that the cricket ovipositor is more like that of ancient cockroaches. It was probably used to deposit single eggs in the ground or in plant stems. Fern fossils found in the same area as cockroach fossils often show a row of slits which could have been made by an ovipositor. At some point in the cockroach's evolution, the eggs were contained within a hardened sac and/or the female's body to protect them from drying and to increase the chance of survival. Most of what is known about ancient cockroaches comes from a study of fossilized wings. There are more wing fossils than of any other part of the insect. Quite often predators will discard wings when consuming the rest of the insect.
The main sensory receptors students will be interested in for the purpose of this investigation are briefly described below. There are others.
This activity nicely lends itself to the cooperative learning approach. Each team of three students should have a Recorder, an Animal Handler, and a Maze Master. The tasks for each individual are described in the student section of the lab.
In order to keep your cockroaches alive and well, their temperature should be regulated so as to stay between 27 degrees to 30 degrees C. For a large culture for classroom use, a 15 gallon aquarium of glass or plastic with or without a lid can be used. A container 30 x 30 cm is large enough for 24 cockroaches. The inside rim of the tank should be smeared with a 2 inch wide band of Vaseline to prevent escape. A few egg cartons, some reversed plastic containers with holes to allow entrance and exit, or some strips of cardboard arranged in layers will provide suitable shelters. A thin layer of sawdust is suitable for the bottom of the cage.
For food, dog food, rat chow, rolled oats, wheat germ, potato, or apple will provide variety for a balanced diet. Water can be provided by the inverted vial method or by placing a piece of dental packing tucked in a small vial. Mold and drowning are sometimes problems associated with water supply. The easiest way to prevent both and to provide nourishment is to keep a fresh slice of potato or apple in the roach habitat at all times instead of the water container.
Each maze should be constructed according to the specifications which follow on the next two pages. White foam core board, which can be purchased at many drug stores and office supply stores, works well for the sides. Plain cardboard is fine for the base. Clear package tape holds the maze sections together. The sections can be cut from the foam core board with a mat knife.
First measure the section and mark it off on the board. Then use the mat knife to cut through the top layer of the foam board. Turn the board over, gently bend upward along the cut, and then with it still in the bent position, use the knife to cut through the remainder of the board. This should provide a smooth section. One piece of foam core board is not quite enough to construct a pair of Y and E-mazes. It takes a bit of time to cut the maze sections and to tape them all together. Enlisting the talents of a student or two might be a good idea.
Once the mazes are constructed, they can be used from one year to the next, making setup time for this activity minimal in the future. Diagrams showing the arrangement of the foam core sections and dimensions are located at the end of the teacher section. Plexiglas can also be used to make the sides of the maze. The easiest way to do this is to ask the local supplier if they will cut the Plexiglas to your specification. Sometimes they charge a little extra to do this. If Plexiglas sides are used, the maze will be durable enough to not require a bottom piece. Use the counter surface as the floor of the maze. This makes wiping with a dilute Lysol solution between trials much easier. The wiping isn't necessary, but does make the experiment more scientifically valid. Sophisticated students will wonder if cockroaches use pheromone trails and the rinsing of the surface with a cleaner between trial runs will eliminate such trails if they exist.
A piece of Plexiglas of standard thickness works well for the maze cover. It is transparent so that the animal's activities are readily observed. It is also rigid and fairly heavy (to a cockroach) so that it fits snugly over the maze sections. This makes it less likely that the animal will escape during a trial run. Plexiglas can be obtained at many hardware stores and frame shops. There are also establishments that deal exclusively in glass and Plexiglas.
The cardboard base can be cut from any box that is large enough. A piece of scrap cut to a length of 5 inches and a width of 2.5 inches (approximately) will be folded in the shape of an inverted "U" and serve as the roach hut. Cardboard cut 3.25 inches wide and 7 inches long will serve as the light barrier by covering the "y" arms as needed. The same barrier can be used on the E-maze even though the arms of the "E" are shorter. Do not let the barrier cover any portion of the long section of the E-maze.
Disposable latex gloves can be ordered by the box from standard science supply companies. Don't buy the clear polyethylene gloves because students will not be able to securely hold the cockroaches. These gloves are not form fitting and are slippery.
The cockroaches can be obtained from a science supply house such as Carolina Biological or Ward's Natural Science Establishment. Order them a month or more before doing the activity. This will allow your students to acclimate to the insects and to become increasingly curious about them. The average cost is $26.00 for 12 animals. Both the adults and the older nymphs can be used in the maze activity.
When all of the materials are ready and the students have received their instructions, the Animal Handler can then pick up the team's cockroach from the teacher. Have the animal in a small plastic container with a snap on lid. A yogurt or sour cream container will be fine.
Once the Recorder is set with the Observations Sheet and the appropriate Maze Outline Sheet, the Maze Master should slide the Plexiglas so that the cockroach can be gently deposited in end of the tail of the Y-maze. They should start with the Y-maze since if offers the cockroach only two options or decisions rather than three as in the E-maze. As soon as the animal is in place, the Plexiglas should be slid back into place to prevent escape!
Initially, the animal should be permitted to explore the maze and students should make ten observations describing the cockroach and its behavior. It should be noted which arm of the Y-maze the cockroach first enters. The opaque cover will be place over the opposite arm when the trial begin.
After the observations are completed, the Maze Master should slide the cover back and the Animal Handler will remove the cockroach and return it to the plastic cup. Allow a minute to pass. A piece of cardboard folded in the shape of a U should be placed at the end of the arm of the "Y" that is going to be covered.
Since Blaberus does not bite and is pathogen free (having come from a science supply house rather than the wild) two of the largest safety concerns when handling animals are immediately eliminated. Be sure to keep the culture tank clean and mold free. If the water container gets dumped and the floor of the container is wet for a period of time, mold may begin to grow. Mold can quickly decimate your cockroach population and perhaps cause allergic reactions in your students.
Caution students when handling the organisms not to squeeze them too tightly and to be careful not to let them escape. If the cockroaches are transported in the small plastic containers and the lids are kept on the mazes during trials, there should be little chance of run away roaches.
The greatest concern during the activity is for the safety and well-being of the cockroaches. With proper discussion before the lab, everyone should be fine - invertebrates and vertebrates alike!
The initial introduction and maze trials will take one class period (45 minutes) and perhaps a little more. You might want to introduce the cockroach to students during one class period and allow them to do the observations run. Tell them not to record Y-maze arm preference.
The next class period could be spent discussing a few of their observations and pointing out the difference between observations and inferences and opinions. Then have them place a new cockroach in the Y-maze and the E-maze and answer the questions. Their homework would be to design the next experiment and have it ready for the next lab session. Their original experiments will take another 45 minute class period.
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