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MADAGASCAR HISSING COCKROACHES

Phylum Arthropoda is subdivided into a dozen or so classes of organisms, including spiders, isopods, millipedes, centipedes, crustaceans (crabs, shrimps, and their kin), and insects. Class Insecta, the largest class of organisms on the planet, is subdivided into 26 orders, one of which is Orthoptera. Members of the Orthoptera include grasshoppers, katydids, crickets, mantids, walkingsticks, and cockroaches. They all develop through incomplete metamorphosis, starting life as a tiny immature replica of the adult, and progressing through a series of nymphal instars leading up to adulthood.

The principal player in the Diversity of Life Course is the Madagascar hissing cockroach. These magnificent insects are large, sleek, clean, slow-moving, and sexually dimorphic. And they hiss. Some students may resist handling them initially, but as they see others in their group handling the roaches, they will gain confidence and join the fun.

There are hundreds of species of cockroaches worldwide. They are essentially nocturnal scavengers, opportunistically eating fruits, grains, and decomposing plant debris. Few cockroaches fly, but many are incredibly fast runners. The hissing cockroach, however, one of the largest of its group, is a plodder, never moving quickly enough to startle a person or to escape.

The Madagascar hissing cockroach is a large, wingless cockroach with a life cycle that is somewhat different from other roaches. The female gives birth to live young after carrying the eggs and newly hatched nymphs for about 60 days. She can give birth to 30–60 nymphs at a time. The nymphs molt six times over the next half year or so before reaching maturity. Hissing cockroaches live 2–5 years.

You can identify male and female roaches by their thorax. The male has a prominent pair of ridges on the top/front of his thorax just behind his head, which are sometimes described as "horns"or "eyebrows." The female has only a slightly raised ridge.

Unlike most of the orthopterans, roaches are silent, with the notable exception of the hissing roach. It hisses by drawing air into the abdomen through spiracles on both sides of the fourth segment, and then forcing it out with a fairly loud hiss.

Why do these roaches hiss? Scientists wondered what advantages a roach might gain from hissing. Males and females (and older nymphs) hiss when disturbed, but scientists also noticed that male roaches sometimes hiss when there is no threat imposed by another animal. They also observed that males hiss in the presence of a female. This led scientists to hypothesize that hissing was involved in courtship, perhaps used by males to establish a territory or to ward off other males.

To test their ideas about hissing and mating behavior, scientists covered up the spiracles on the fourth segment of one male roach and left them open on another male. Both male roaches were placed in a cage to see which would become dominant. The hissing male almost always became dominant.

In other experiments they found that the male that hissed the loudest almost always drove off the other males. When a hissing male and a nonhissing male were placed in a cage with a female roach that was ready to mate, the hissing male was able to fight off the roach that couldn't. The hissing male was more likely to mate with the female, and pass on his "hissing" genes. In fact, females would not mate with a male that couldn't hiss.

Caring for cockroaches. Hissing roaches need food, water, warmth, and cover. Use a terrarium as the habitat; its size will depend on the number of roaches you will be housing.

• Get a large aquarium that has a secure fine-screen cover. In the kit is a plastic 6-liter basin with a lid. Hissing roaches are excellent climbers and can easily scale the side of a glass terrarium. One way to prevent this is to apply a band of petroleum jelly 4 cm (1-1/2") wide all the way around the inside of the terrarium near the top. Roaches will not cross the sticky barrier.
• Cover the bottom of the terrarium with sand, soil, or wood shavings. Put in lots of stuff for the roaches to crawl into and under for cover. Slightly flattened paper-towel tubes, paper egg cartons, chunks of tree bark, and the like will work. Roaches are thigmotaxic, meaning they like to have physical contact with some structure for security. Hissing cockroaches are more likely to hiss when there are objects in the habitat container.
• Place food in a shallow dish like the lid of a margarine container. Small bits of vegetables, bread, dry dog food, crackers, and fruit are good. Don't worry if the fruit starts to mold; the roaches seem to like it that way.
• Place a cotton ball or piece of sponge in a small dish (like a small plastic cup, cut so it is a centimeter tall). Keep a little water in the cup at all times.
• Place the terrarium in a warm location. If the temperature is likely to drop below 20°C (68°F), keep a low-wattage lamp on one end of the terrarium.

Breeding. If you are interested in breeding your cockroaches (a good idea, as they can be costly to acquire!), set the terrarium up as described, but cover the bottom with soil rather than sand. Keep the terrarium soil and bark slightly moist (not wet) at the end away from the food, water, and heat. Hissing cockroaches give live birth, and the newborns seem to thrive in a slightly moist environment.

Before the investigation. In preparing for the food-preference part of the investigation, put your roaches on short rations. Remove food and water sources 2 or 3 days before that part. The roaches can go without food for 2 or 3 weeks, and without water for a week. Make sure they are not deprived of access to food and water for longer than 5 days.

Cockroach sources. Contact a local high school or college life-science department to see if you can get a gift or a loan of a dozen cockroaches. Pet stores sometimes have them for sale, and biological supply companies usually sell them as well. You might also search the Internet for Madagascar hissing cockroaches. A surprising number of sites offer roaches for sale. Shop around—prices vary widely. Also be aware that currently some states will not allow hissing cockroaches to be shipped into the state (Florida for example).

If at the end of the course you have no desire to maintain the colony, try to find a colleague, biological supply house, or zoo to take your colony. The roaches are valuable, and you should easily find them a new home. If you are left with no alternative besides euthanasia, bag and label the colony and place it in a freezer for a couple of days. Cockroaches should never be released locally.

What to do when they arrive. Release roaches into prepared container (see above) with plenty of ventilation but with a tight lid, as they are quite strong and can otherwise escape.

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