Biology and Captive-Breeding of the Giant Cockroach Blaberus giganteus (L.)

by Stephen W. Bullington

Adult Giant Cave Cockroach Resting on Branch

Fig. 1.--Adult giant cockroach.

The cockroach Blaberus giganteus (L.) is the largest species in its genus and one of the largest cockroaches known. Individuals can measure over three inches (88 mm) in length and one and one-half inches (38 mm) in width. In spite of their extended dimensions, Blaberus giganteus are lightly-built, sprightly roaches, with bodies that are much broader than deep. This flattened body allows them to squeeze between cracks to hide from predators. Blaberus giganteus is found in parts of the West Indies, in Panama, and southward into northern South America.

This species is now appearing on the pet market because captive-reared specimens are readily available from research labs in entomology. The giant roach has been a common experimental animal in entomology labs since the early 1950's.

Blaberus giganteus have a number of features that make them good lab animals, and consequently good pets. First, of course is their great size. Second, they are very easy to rear; a number of adults and developing young can be kept together in the same container. Third, they have a relatively long adult life. Fourth, they are much too large and temperature dependent to ever survive a winter outdoors in the continental United States. The only exception to this last statement might be in south Florida, and for a number of reasons it is very unlikely they could survive even there.

But their greatest appeal is that for a few dollars and a small set-up you can bring one of the most famous denizens of the Carboniferous coal forests right into your own den or study, and with a minimum of effort watch most of its daily activities. Not of course that these large roaches are closely related to their long-dead relatives that ran up the boles of tree ferns 200 million years ago. But they are the closest thing to these ancient roaches man will ever be given to see-and very much the same size. Simply reading about these roaches or seeing them for a minute or two in an insect zoo cannot compare with actually watching them over an extended period of time in your own home.

Biology

The only visible difference between the sexes is on the last abdominal segment, which is the one that bears the "cerci." These cerci are present in both males and females, and look like a pair of short, rear-end antennae. Just between the cerci of the males is a pair of hair-like appendages called "styli." Styli are absent in the female.

These tiny styli can be hard to see. Fortunately, the sexes can also be distinguished by their behavior--males frequently engage in a courtship ritual, females do not.. Several times during this ritual the male raises his folded wings so that they are almost at right angles to his abdomen. He also makes trembling movements with his abdomen. The remainder of the ritual has never been described in the scientific literature, although in any large colony the entire sequence can be observed almost continually. During mating the pair assumes an end-to-end position, with their abdomens joined at the tip. They will stay in this position for many hours, sometimes even overnight.

Eggs resulting from a successful fertilization are retained within the female in a compartmentalized case, or ootheca. This ootheca forms outside the body of the mother, and, while forming, appears to be projecting from the tip of her abdomen. Here, it is rigid, about one-half inch in length, and looks like an elongate briefcase or lady's purse. After hardening a little, it slides back into the mother's abdomen, into a cavity called the brood pouch. It remains in the pouch until just before the eggs hatch. Birth consists of extruding the ootheca and letting the young roaches wiggle out of the eggs. Birth takes less than ten minutes.

Occasionally the ootheca will be deposited outside of the mother long before the roach embryos have developed. This amounts to an abortion. Just why this happens is not known. Perhaps abortions are brought on by such unfavorable conditions as poor food quality or overcrowding.

A litter consists of about 20 young, each a tiny, dark brown nymph one fourth of an inch long. These nymphs eat the remains of the ootheca as their first meal. Both young and old nymphs avoid light, and by day either hide under objects or burrow into the substrate in the tank At night they emerge from their hiding places. When foraging on the surface, smaller individuals are very alert. Their antennae are constantly in motion, sometimes even quivering. Older nymphs are flattened and when viewed from above somewhat resemble trilobites. I personally think these large nymphs are quite beautiful.

Last Instar Nymphal Giant Cockroach in Branch Crevice

Fig. 2.--Large nymphal giant roach.

To grow, the young roaches must molt or shed their skin. Each time they cast off their old skin, the new one replacing it has slightly more surface area, providing room for additional tissue to be added later. The new skin is at first soft, pliable, and colorless white. It takes several hours to harden into an exoskeleton. During this time the roach is supported by hydrostatic pressure. This alternation of an exoskeleton with an hydrostatic skeleton occurs seven to eight times prior to adulthood, over a period of four to six months. The adults differ from nymphs by having wings and functioning sexual organs. They may live for an additional 20 months.

Freshly Molted Gaint Cockroach Nymph on Philodendron Leaf

Fig. 3.--Freshly-molted nymphal giant roach. Note wing pads and soft white cuticle.

Adults have two pairs of wings, which fold back, flat over the abdomen. At the last molt these wings first appear as wrinkled sacks where the rigid wing pads had once been. Within a few minutes they gradually expand to assume their final shape, and within a day begin to show their final coloration. When fully developed and hardened, the anteriormost pair are elongate in form, leathery in texture, and light yellow in color. They protect the second or hind pair, which are whitish clear, delicate in texture, and have the supporting veins arranged like a fan in a radiating series of straight lines. The roaches use the hind wings for flying or gliding. Active flight is preceded by a short period during which the roach vibrates its thorax. Both active flight and the shivering preparatory to it are uncommon occurrences.

Freshly Molted Adult Cockroach, Just Before Expanding WingsFreshly Molted Adult Cockroach, Just After Expanding Wings

Fig. 4.--Freshly-molted adult giant roach on left; note wrinkled wing sacks prior to expansion. On right the same roach a few minutes later, now with wings expanded.

Adult Giant Cave Roach with Wings Spread

Fig. 5.--Photo from old book of dead, pinned adult giant cave roach with wings spread in manner of a butterfly. Note large area and fan-like shape of hind wings. Photo by Edward Step (In Marvels of Insect Life, 1916).

Captive Breeding

The best type of rearing container is a all-glass tank. For a healthy colony starting with, say 15 adults, the tank should be at least 15 gallon capacity and preferably a 20 or 29 high. The roaches should be provided with a branch that has been bleached and sterilized. A piece of driftwood works well. The adults and larger nymphs will align themselves along the branch with their heads pointed upward and their bodies oriented vertically.

The best substrate for the roaches is non-toxic pine chips. The chips should be kept as dry as possible to prevent mite infestations. The roach tank should have a top. The best tops are the screen ones designed to convert aquaria into containers for reptiles and small mammals. The mesh on these tops is large enough to let smaller roaches get through. This problem can be fixed by cutting an insert of metal window screen, and fitting it inside the housing for the hardware cloth that is already there. This precaution is only necessary if the branch you are using touches the top at any point. Giant roaches use only their claws to climb. They cannot cling to glass surfaces.

For this reason, food and water must be provided in containers with roughened surfaces, to allow access for smaller individuals. Food can be provided in the glazed concrete water bowls sold for reptiles. These bowls have a rough surface. They also have the advantage of a naturalistic design and colors that blend well with the yellows in bleached wood and wood chips.

A steady supply of fresh water is essential to maintaining a healthy colony. Use a modified chick waterer which has a pre-cut sponge in the trough (Cat. No. 14-W-7510, Ward's Nat. Sci., Estab., Inc., Rochester, New York). Pile the pine chips up to but not over the edge of the sponge.

Watering Device Designed for Cockroaches

Fig. 6.--Chick-waterer with sponge for roaches.

Giant roaches do wonderfully well on a steady diet of cereal, meat loaf, and apples. Use a whole-grain oat cereal like "Cheerios" (made by General Mills). The roaches particularly seem to relish the sugar-coated versions. The meat loaf provides protein, an absolute must if the roaches are to grow. It would not be a stretch to say giant roaches were partially carnivorous. Thirty to forty adults and large nymphs can finish off a cup of cooked hamburger in less than an hour. If you do not give them protein they will get it on their own, by attacking and eating their molting or aged cage mates. Chewed or brown wing tips are an early warning that protein is lacking.

Shoot for the highest temperature you can get, in the upper 70's or low 80's, and for low humidity. The best way to accomplish both is by focusing a spot lamp on part of the tank, and preferably on part of the branch you have placed in the tank for the roaches to sit upon. The light should be set on a timer with 6 hours of light and 6 of darkness.

In summary, Blaberus giganteus are long-lived, innocuous insects with interesting behavior and development. All available individuals are captive-bred, and are both too large and too tropical to exist as reproducing feral animals within the continental United States. Further, captive care and breeding are extremely easy. All-in-all, they make a most suitable "pet" insect. They also make wonderful food for tarantulas and some reptiles and amphibians. The latter seem to prefer teneral or just-molted individuals, perhaps because at this time of their life they are so soft and tender.

Selected References

Piquett, P. G. and J. H. Fales. 1953. Life history of Blaberus giganteus (L.). Journal of Economic Entomology 46(6):1089-1090.

Rehn, A. G. and M. Hebard. 1927. The Orthoptera of the West Indies. Number 1. Blaberidae. Bull. of the Am. Mus. of Natural History 54:1-320.


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