The Hissing Cockroach, Gromphadorhina portentosa (Schaum)

by Stephen W. Bullington

 

The hissing cockroach, Gromphadorhina portentosa (Schaum), has lately been offered for sale in the pet trade. This large, docile roach is probably familiar to most people. For years it has been featured in various educational demonstrations and insect zoos. In these exhibitions, large specimens are often taken from their cages to be handled by children. While being handled, the roaches usually hiss loudly--and harmlessly--giving rise to the name "Giant Hissing Cockroach." The roach is also known as the "Madagascar Hissing Roach," referring to the origin of the species in the tropical forests of that island. Specimens in the pet trade are sometimes sold under the name of "Madagascar Hissing Beetle," perhaps to cover the negative impressions generated by the word "cockroach."

The adult roach does resemble a large beetle in its apparent lack of wings and shiny upper surface. But unlike a beetle, the roaches really do not have wings or even wing pads at any stage in their life history. The roaches are a dark chocolate brown with dark orange makings on the abdomen. Adults can measure up to 10 cm long and weigh up to 24 grams.

It is this large size--as big as a small mouse--and the ease with which these roaches can be reared that recommends them to those who are looking for large invertebrate prey for insectivorous lizards and tarantulas. A peculiar advantage is that these hissing roaches do not have any odor associated with them or their feces. A breeding colony of several hundred large individuals can therefore be easily maintained in a 15- to 20-gallon aquarium without odor, something that cannot be said for either mice or for other large roaches. The practical utility for someone who wants to rear their own large insect food in the room of a house is obvious. Last, as I hope to show in the ensuing article, the roaches are incredibly interesting in their own right.

Life History

Female hissing roaches lay their eggs in a purse-like capsule known as an ootheca. This egg case is retained within the body until the eggs hatch, and the young roaches first see the world as tiny nymphs. You may occasionally see a female with the ootheca extruded. Such a female is in the process of forming the ootheca. Once it is completely formed she will retract it into a special cavity in the tip of her abdomen.
A female that has been successfully fertilized will retain the eggs within this cavity for at least 60 days. These females may be left with the colony. Once born the young nymphs will not be eaten by the adults. This fact makes it possible to keep all stages of hissing roaches together in the same container.

Although the nymphs are similar to the adults in many respects, they are not just miniature copies. Nymphs of different ages also differ from one another, in both their proportions and their coloration. Older individuals are a dark brown. The most obvious difference is between mid-sized individuals and adults. Mid-sized roaches are more oval in outline than adults when viewed from above.

The nymphal roaches must molt, or shed their skin, several times to reach adulthood. This process is similar to molting in lizards and snakes. But in the roach both new and old skin are proportionally thicker than the skin in lizards and snakes. This is because in the roach the skin doubles as its skeleton, portions of it being hardened to form flexible plates that articulate with one another. This light-armor casing is never shed in pieces as in some lizards. In hissing roaches, the skin or casing splits down the middle of the back and the roach slowly wiggles its way out. The newly-molted roaches are very whitish. The new skin takes many hours to harden, and as it does so the roach gradually darkens to its normal coloration. Meanwhile the roach has a bloated look because, during and just after the molt, it is supported by hydrostatic pressure rather than by skeletal plates. It is while in this hydrostatic pressure period that the roaches make the best food for tarantulas.

The nymphal roaches will molt six times during the course of their lives. The last molt occurs about five months after the nymph was born. At this last molt the nymphal roaches become sexually mature adults. Adult roaches never molt again. They may live for two or more years.

Adults can be sexed by three methods. The easiest is to look at the thorax. The thorax is the second of the three sections into which the roach body is divided. The first section is the head, and the third one is the abdomen. The part of the thorax that is just behind the head is called the prothorax. In both sexes the upper surface of this prothorax is developed into two protuberances. In the females the development is slight. In the male, in contrast, the protrusions stand out, making the prothorax appear to be the head of a vertebrate animal.

The second way to sex the roaches is to look at the feelers or antennae. The antennae are long, whip-like structures found on the head. Adult males have antennae with many laterally-projecting sensory hairs. These hairs give their antennae a fuzzy look, especially near the base. The antennae of the female lack these hairs.

The third way of determining sex is to look at the tip of the abdomen, or third section of the body. At the tip of the abdomen there is a ventral plate. In the male this plate is much narrower than in the female.

Adult Biology

In nature, hissing cockroaches are found on the floor of forests in Madagascar. Like most cockroaches, they are active only at night. They hide under debris during the day. In captivity, the roaches continue this pattern. The one feature of the roach that might attract attention during the day is their hiss. All stages of the roach can hiss. Often an entire colony will hiss loudly if their container is bumped. Sometimes a colony will hiss for no apparent reason.

The hiss is produced by a pair of spiracles, or breathing tubes, on the fourth segment of the abdomen (counting from the front). A pair of spiracles is present on most of the abdominal segments. These spiracles allow air to seep deep within the tissues where it can oxygenate the muscles. The spiracles also allow carbon dioxide to diffuse outward and escape from the body. All the spiracles have a constant inflow and outflow of gases, however, those on the fourth segment have been modified to take advantage of this flow to produce a sound, much as in a wind instrument. The amount of air exiting the spiracle has also been increased by the development of air sacks within the body. These sacks act like bellows.

In addition to hissing as a colony, the roaches also hiss individually, mostly at night. Adult males hiss when fighting, courting, and copulating. Two types of hiss can be discerned during courtship. Males will also hiss when disturbed, as will females and nymphs.

Adult roaches can also signal their intentions using postures instead of sound. In fact, they have quite a repertoire of postures and stereotyped movements. Aggressive movements include flicking their abdomen, pushing with their abdomen, butting with their pronotum, and lunging with their entire body. Submissive behaviors include crouching and retreating. Other behaviors include extending their abdomen, thrashing their abdomen, and standing on their toes (so-called "stilting"). Most of these movements are used in encounters between competing males. Abdominal extension may be correlated with release of an air-borne chemical, or pheromone.

The roaches use this many-faceted system of communication to signal each other in a dominance hierarchy involving territories. One adult male defends a territory around several adult females. He courts and mates within this territory. Other adult males are not allowed in. Intruding males are pushed out using the ram-like pronotal projections. A male may hold the same territory for several months, leaving only to feed. Females and nymphs may enter and leave a territory as they please.

Males that get pushed out of a territory do one of two things. First, they may group themselves just outside the perimeter of the territory. These males are called "satellite" males. Satellite males may move about from territory to territory and even on occasion may fight with one another or with males holding territory. If for some reason one of the territorial males becomes disabled one of the satellite males will replace him. Second, a male may place himself as far away as possible from other males to avoid fighting. Non-fighting males are called "subordinates." Females can tell to which category a male belongs. Females approach territorial males for mating more often than they approach satellite males, and approach satellite males more often than they approach subordinate males.

Courtship begins with the male and female stroking the other's antennae with their own. The pair then proceed to body stroking. All of this antennal stroking is accompanied by a subdued mutual hissing. Once attached to each other, male and female stretch out so they are facing in opposite directions. They may remain in this position for 20-30 minutes.

Husbandry

The hissing roach is easy to keep and breed. A minimum set-up consists of a 15- to 20-gallon all-glass aquarium, Vaseline, and a supply of dog food and water. Amenities include some sort of a substrate and some provision for concealment. Ideally, about an inch or an inch-and-a-half of pine shavings should cover the bottom of the aquarium to absorb water and feces. Although some sort of substrate should be present for hygienic and aesthetic reasons, it is not absolutely necessary for the health of the roaches. Cedar chips should be avoided. The turpines emitted by these chips may retard or inhibit nymphal growth, much as they retard the growth of clothes-moth caterpillars in cedar chests. Whatever is used as a substrate, it should be replaced about once a month. Substrate that is not replaced will eventually develop a mite infestation

Housing should be kept simple. In set-ups for breeding only, places of concealment can be provided by rubber-banding four or five paper tubes together. The long tubes found inside paper-towel rolls are better than the short tubes found inside toilet-paper rolls. Heavy FAX-paper tubes work best. One disadvantage of the thinner paper tubes is that if the tube brushes up against a water dish, it will eventually absorb all the water and disintegrate. A permanent set-up can be provided by bolting a number of sections of particle board together, spacing them out with thick washers or small wooden blocks to provide hiding places. This particular method is used by most departments of entomology.

If you are interested in observing the roaches rather than just rearing them for food, a set-up with more floor space is required, for example one of the thirty-gallon "long" all-glass aquariums so popular for colubrid snakes. The floor of the aquarium should be covered with pine shavings. Flat stones can then be distributed on top of the shavings to produce a number of natural territories. Stones having a top surface area of about 20 square cm are ideal. Males will set up one territory to each stone, and will be surrounded by an assortment of females, nymphs, and satellite males. Subordinate males will stay off the stones.

In all these set-ups the one essential is a heavy layer of Vaseline around the top edge of the aquarium. This layer of Vaseline should be about one inch in width. The purpose of this Vaseline is to keep both nymphs and adults inside the aquarium. Although supposedly ground dwellers, all stages of this roach have no difficulty in walking up the glass side of a terrarium and escaping. To those of you familiar with tarantulas this ability should come as no surprise, and is produced in the same way--i.e. by thousands of tiny hairs on the tarsi, or tips of the legs. But what is surprising is that these roaches can remain sticking firmly to the glass even after they have been grasped, much as can some geckos. This applies not only to the tiniest nymphs but also to the largest adults. So beware.

Although not essential for keeping the roaches in, a top is a good idea, both for peace of mind and to keep other animals out. An ideal top for all-glass terrariums can be made by cutting a piece of glass to size, i.e. to fit tightly into the grooved area, and then drilling two inch-and-a-half diameter holes, spaced in a few inches from each end. Professionals glass-cutters should route-out the holes in the glass. Tight-fitting wooden frames with screen inserts can also be constructed to fit all-glass terrariums. These will also work on older terrariums with metal frames. A less time-consuming alternative is to use an extra large version of one of the plastic terrariums used in the pet trade. The snap-on lid of soft plastic will keep out mice, as well as keeping most of the roaches in. These terrariums also have the advantage of being stackable to increase humidity. The Vaseline is still necessary, however, as the smaller roach nymphs can easily squeeze through the air slits.

Hissing roaches will eat almost any type of dry feed. Standard dog-food biscuits work fine. So does iguana food or rat chow. The author provides his colony with chicken feed in addition to dog food. The roaches should also be provided with fresh greens on a weekly basis. Celery and lettuce are good choices. But the roaches love carrots above all other greens. A small colony can eat a large carrot in a day.

The roaches also need a constant supply of water. Water can be supplied in a small plastic crock stuffed with some absorbent material. The idea behind the absorbent material is to keep the roaches from falling in the crock and drowning. The best absorbent material to use is polyester fiber. Because it is synthetic it will not mold. One can also use cotton. The best set-up, however, is to use a chick-waterer with a circular piece of sponge.

Temperature and humidity do not appear to be very important. But keep in mind that the roaches are tropical animals. They probably prefer temperatures of about 80 degrees F and relative humidity's of about 65%.

Summary

The hissing cockroach is large insect that can be easily cultured as food for insectivorous reptiles and large tarantulas. It is also a true "pet" arthropod--one of the few--that is tame and docile and can be handled safely by children. Further, for those that are interested, it has an complicated social system that could bear further study. All in all, it is an insect that is most extraordinarily suited for captive propagation and study by private individuals.