Figure 1: Adult male Madagascan giant hissing roach. Actual size.
Would you invite these exotic animals into your classroom? They are guaranteed to attract a crowd! Madagascan giant hissing roaches, Gromphadorhina portentosa, are spectacular insects that instantly draw the attention and curiosity of students and are very easy to care for and handle. Large and easy to see, Madagascan roaches are ideal for classroom observations and science projects. They are slow moving, wingless, docile, have little or no odor, and do not bite. Known as "living fossils," these insects are very similar to the prehistoric cockroaches that lived on Earth long before the dinosaurs. With appropriate supervision, even young students can handle them.
The cockroach family, to which Madagascan roaches belong, is among the most primitive of the winged insects. The nearest relatives to cockroaches include mantids, grass-hoppers, stick insects, and termites (Cornwell 1968). The fossil record shows that roaches were very abundant during the Carboniferous period, 250 million years ago. There are at least 3,500 known species living today, in 450 genera, most of which originate in the tropics.
As a group, cockroaches exhibit a wide diversity of sizes, colors, and habits. Although they have an infamous reputation as household pests, in reality only about half a dozen species (less than one percent of all known forms) have negative associations with humans. Many species are diurnal, some are semiaquatic, others live in the ground or are wood-boring. Some, such as the Madagascan roach, do not have wings. About a dozen or so species live commensally in the nests of ants, wasps, or termites. There are also roach species that inhabit caves with bats or live in the desert. The majority of cockroaches in tropical countries exist as scavengers outdoors, feeding on vegetation and organic matter in an apparently harmless fashion.
Figure 2: Side view, illustrating differences in the thorax and antennae in female (top) and male (bottom) Madagascan roaches.
The Madagascan giant hissing roach is a large (adults, 2-3 inches long and 1 inch wide), wingless member of the cockroach family (Fig. 1). This insect is native to the island of Madagascar, off the eastern coast of Africa, where it appears to play the ecological role of scavenger on or near rotten logs in savannah areas. Little is known of its behavior in the wild. (The Madagascan roaches supplied by Carolina Biological are captive bred in the United States and are not collected from the wild.) Recently, these roaches have become very popular in museums, zoos, and classrooms for hands-on explorations of insect morphology and behavior, and as an example of the importance in the web of life (ecosystem) of an "unhuggable" organism.
Madagascan roaches exhibit sexual dimorphism, meaning that males and females look or act differently. Sexual dimorphism is common in animals where males and females have distinct roles in mating and courtship (e.g., the male deer with antlers, the colorful male peacock, and the male cricket that chirps loudly to attract females).
Male Madagascan roaches have prominent protrusions, called pronatal humps, on the thorax, which look like horns. Females have a smoother thorax with very small bumps or none at all. Also, the antennae of males are much brushier than those of females (Fig. 2). Fraser and Nelson (1984) have studied communication and behavior in laboratory colonies of these insects, and they observed that male Madagascan roaches establish territories that are defended from other adult males. Aggressive hissing and posturing behavior is used to warn intruders away; males use their pronatal humps as rams in combat to physically defend territories. These interactions do not seem to result in injury or death. Females are gregarious and do not fight among themselves or with males. Numerous females and nymphs (immature stages) are permitted into male territories, with courtship and mating often occurring within the territory.
The species is unusual among insects in that the females appear to bear living young. Actually, the young emerge from an egg case (ootheca), which has been retained within the body of the mother. This is known as false ovoviparity. The ootheca is whitish and about an inch long. It is divided into many compartments, each of which contains an egg. Sometimes stressed females release the egg case before the eggs can develop. Gestation is usually about 60-70 days. Normally, a female gives birth to 20-40 babies, known as nymphs, over a two-day period. Each nymph is about 1/4-inch long (about the size of a small watermelon seed) and very flat. The young may remain grouped around the female for some time after emerging as she protects them by raising her body over them (Cornwell 1968).
The nymphs, which resemble miniature adults, grow fairly rapidly. They usually go through six molts, reaching adult size in the seventh instar (or stage). The young Madagascan roach needs to molt (shed its exoskeleton) as it gets larger, since its hard, outside covering does not expand very much to accommodate the growing insect. Grasshoppers, praying mantises, and termites, which are close relatives of the roaches, develop in the same way. When a nymph is about to molt, you see a crack in the lengthwise line on the back of the insect. The exoskeleton has split and a white, black-eyed, larger-sized roach emerges. Within a day, the color darkens as the new exoskeleton hardens. The newly emerged cockroach usually recycles nutrients by eating the shed exoskeleton. Nymphs reach maturity in five to ten months, with faster maturation at higher temperatures. Adults may live for two to three years.
The Madagascan giant hissing roach is notable for its unique ability to produce an audible hiss. This sound is produced by pushing air forcefully through a pair of modified spiracles (openings in the abdomen of insects that are normally used for breathing). In the classroom the hissing response is most often observed when roaches, unaccustomed to being handled, are picked up. This is one of the few defensive behaviors that this harmless insect has to avoid predators. The roach also tucks its small head and antennae under the thorax. The thorax then resembles the large head of some aggressive and noisy animal!
Madagascan hissing roaches also use hissing as a means of communication. Hissing in response to a disturbance may signal the presence of danger to other roaches. Adult male roaches hiss during aggressive encounters (defending territories against other males), and during courtship and mating. Females and late-stage nymphs hiss only when they are disturbed or threatened.
Nelson and Fraser (1980) reported that the Madagascan giant hissing roach has evolved a sound-signaling system that appears to serve for communication and maintenance of social structure. They measured the acoustical characteristics of hisses associated with some social displays in the species and described how hissing was incorporated in the social displays.
Nelson and Fraser identified five distinct hisses that were highly correlated with specific interactions, depending on whether defensive signaling, territoriality, or courtship was occurring. Males that were muted so that they were unable to hiss were almost never successful at mating with females. The researchers concluded that, while behaviors other than sound production (such as olfactory clues) are important in courtship and aggressive interactions, sound plays an important role in communication, and it may be necessary at one point in courtship.
Most of the time (75 percent), Madagascan roaches are not very active. A clear shoebox is fine for a pair of roaches; a few holes are needed to provide air. If the lid is not very tight-fitting and secure, tape the lid shut around the edge. If a pet box with a snap-on lid is used for pregnant females, place a square of muslin or light cotton over the top of the cage. Use the lid to hold the covering in place so that newly emerged nymphs will not escape through the openings in the top. Madagascan roaches are strong animals that have been known to escape and wander, and nymphs can fit through small spaces! While they are not adapted to living among humans, as are their more prolific and faster-moving cousins, the German and American cockroaches, Madagascan roaches are potential household pests. Use caution in securing your cage.
Figure 3: Electron micrograph of Madagascan roach limb, showing hooks and sticky pad used in climbing. 50x actual size.
Wood chips or bark are good substrates for the bottom of the cage and provide hiding areas. Gravel, pine shavings, or crushed corncobs are also acceptable coverings for the bottom of the cage. You may also provide half an egg carton or a cardboard roll from paper towels for hiding spots, and you may add a branch for climbing. In a cage with just a few roaches, the substrate should be replaced about every four to six months as needed. If your roaches have been breeding, the material should be sieved to avoid throwing away small nymphs.
Place the cage in a warm location, as Madagascan roaches are tropical. They seem to do well at room temperature (72-76 degrees F). At higher temperatures (80 degrees F) they are more active and may breed; and at lower temperatures (66 degrees F) they are sluggish and will probably not breed. Although they survive brief exposure to lower temperatures (above freezing), do not keep Madagascan roaches at temperatures lower than 65 degrees F or higher than 85 degrees F. Unless you plan to breed the roaches or have a poorly heated room, you should not need an additional source of heat.
Madagascan roaches are nocturnal, meaning they are most active at night. One way to observe the night-time activities of the insects during the day is to reverse the photocycle (Bell 1981). Outfit a fairly dark room or closet with a 100-watt light and timer that will turn the light on from about 6:00 PM to 6:00 AM for 12 hours of light. The roaches will be active from about 8:00 AM to 4:00 PM. Best results for behavioral observations will be obtained if the terrarium stays in a dark room, with a red light for illumination during daylight hours. A 40-watt red incandescent bulb may be purchased in most stores with a varied selection of lighting supplies. You can see the roaches, but they perceive that it is night and go about their normal nocturnal activities.
Feed your Madagascan roach dry dog, cat, or rodent food supplemented with pieces of fresh fruits and vegetables. Good fruits and vegetables for these insects include orange slices, banana peels, carrots, apple, grape, sweet potato peelings, potato slices, etc. Use small pieces (1 inch square or less) and feed moist food sparingly, since high concentrations of fermentation gases are harmful. Remove moldy food regularly. Provide water with a damp sponge in a small cup or dish.
When handling a Madagascan roach, pick up the insect very gently around the thorax (the hard section behind the small head). Be careful not to jerk, since the feet have sticky pads and hooks that grip tightly (Fig. 3). If you pull too hard, you may injure the insect. Let the roach crawl from your hand to another person's hand. It will not move very quickly, and it will not bite. These insects are not fragile, but you should always be gentle with them.
It is fairly common to see tiny light-colored creatures, called mites, crawling on your roach. Just as dogs get fleas, Madagascan roaches sometimes carry mites. These mites only live on the roaches, and will not harm or live on humans. Mites can be removed by gently shaking the roach in a plastic bag with a small amount of flour (the "shake and bake" method). The mites fall off the roach into the flour. Tie off and discard the bag, and gently spray the excess flour off the roach with plain water from a plant mister or wash bottle. Mites may also be removed with a small paintbrush. Repeat the treatment if mites reappear. There is another kind of small mite that occasionally infests food; it can be controlled by discarding old food and changing litter.
Figure 4: With the proper introduction, most children find Madagascan roaches to be fascinating and fun.
An article of this scope can only begin to touch upon the many educational uses of Madagascan roaches. We recommend that for high school to college students, you consult William Bell's excellent book, The Laboratory Cockroach, which includes experiments of varying complexity for the study of the anatomy, morphology, physiology, and behavior of roaches. This book should be available through interlibrary loan from most universities with an entomology department or a fairly extensive library. Since Madagascan roaches are relatively expensive animals, experiments that involve dissection or sacrifice of the specimen may be confined to other large, less expensive genera, such as Blabberus or Periplanata.
Younger students can conduct simple observational experiments using Madagascan roaches (Fig. 4). The our other article on roaches, "Encounter with an Unhuggable" was excerpted from a program presented to teachers by Fran Ludwig (K-5 Science Specialist, Lexington Public Schools). The program is designed to use children's natural curiosity about "critters" as an opportunity to teach them to overcome their fearful or negative preconceptions about insects and to learn to think critically and test hypotheses. The exercises can be performed with other insects and critters as well.
Bell, W.J. 1981. The Laboratory Cockroach: Experiments in Cockroach Anatomy, Physiology, and Behavior. Chapman and Hall, London.
Cornwell, P.B. 1968. The Cockroach (Volume 1): A Laboratory Insect and an Industrial Pest. Hutchinson & Company, London.
Fraser, J., and M.C. Nelson. 1984. Communication in the courtship of the Madagascan hissing cockroach: Normal courtship. Animal Behavior 32:194-203.
Kneidel, S.S. 1993. Creepy Crawlies and the Scientific Method: Over 100 Science Experiments for Children. Fulcrum Publishing Company, Golden, CO. Nelson, M.C., and J. Fraser. 1980.
Sound production in the cockroach, Gromphadorhina portentosa: evidence for communication by hissing. Behavioral Ecology and Sociobiology 6:305-314.
Wolkomir, R. 1993. The bug we love to hate. National Wildlife (Dec/Jan).
Young Entomologist's Society, Inc. 1993. Caring for Insect Livestock: An Insect RearingManual (Special Publication No. 8). Young Entomologist's Society, Lansing, MI.
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