Madagascar Hissing Cockroaches  (zo lab 075)

History of the colony | Student Research with the colony

Gromphadorhina portentosa

The fine folks at Oklahoma State University provided our roaches.

Africa and the island of Madagascar The wingless "hissing cockroach" is native to the island of Madagascar off the southeast coast of Africa. The climate on the world's fourth largest island ranges from tropical rain forest on the eastern coast through savanna to arid regions in the southwest. Madagascar is best known for its Lemurs and Chameleons.

Our Colony is Established
We received a mixed group of approximately 50 Madagascar hissing cockroaches from OSU on January 26, 1999. The sizes ranged from 1.5 cm to 7.5 cm. We guessed that six of the females might be "pregnant" because of their enlarged abdomens. They were placed in a different aquarium from the main group.
    It is relatively easy to see the difference between males and females by looking for the tubercles, or "bumps" on either side of the prothorax. More information about the visible differences between males and females of the species.

The First Birth in the Colony
A female roach giving birth A 6.5 cm female gaving "birth" to approximately 60 nymphs between 1:45 and 2:15 pm on January 28, 1999.
This species of roach is ovoviviparous, producing eggs that hatch within the female's body. After fertilization, the eggs are incubated in a special brood pouch for approximately 60 days. During this time all nourishment is provided by the egg yoke. The mother's body only provides a safe environment for the eggs. The nymphs were observed consuming the brood pouch lining almost immediately after hatching.
A close look at the nymphs A closer look at some of the 1 cm nymphs and the brood pouch lining.

The nymphs undergo six molts, requiring about five months to become sexually mature.

Brood #1 Record

Original Growth of the Colony

  1. January 28, 1999 - Brood #1, 60 nymphs hatched in a separate tank.
  2. February 10, 1999 - Brood #2, 15 nymphs hatched in the main colony tank.
  3. February 20, 1999 - Brood #3, 41 nymphs hatched in the tank with Brood #1.
    • The difference in brood size is interesting. Could it have anything to do with the fact that there are so many individuals in the colony tank while the female in with Brood #1 was the only adult in the tank? This is something for us to follow up on. A population count was conducted in the main colony tank on March 3, 1999. There were 41 females, 30 males, and 15 nymphs.
  4. March 10, 1999 - Brood #4, 31 nymphs hatched in the main colony tank.
    • The number of nymphs in this brood suggests that the size of the population in the colony tank has little effect on brood size.

A Young Adult Sheds its Exoskeleton
A female roach molting A female from the colony was photographed shedding her exoskeleton on February 11, 1999. This is the sixth of seven pictures. The time between the first and last pictures is 73 minutes.

Picture 1
Picture 2
Picture 3
Picture 4
Picture 5
Picture 6
Picture 7

We watched as she would draw in air, swelling the soft body to split the old exoskeleton. The old exoskeleton would slide lower on her body each time she did. Resting from 30 seconds to 3 minutes between each move, she never appeared to use her soft legs to pull free. Fifteen minutes passed between the sixth and seventh pictures. She moved about 2 inches between these two pictures. You can see that the new exoskeleton has returned to a more normal shape in the last picture. This event took place late in the school day and we were unable to observe how quickly the new exoskeleton hardened. By the next morning, she was a uniform black color and moving normally. We made no measurements of size for fear we might hinder her obviously difficult ordeal. Although we have no empirical data, she is obviously larger than before the process began.

Student Research with the colony

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