This week we leave behind the tropical forests of Malaysia and Australia where we met gorgeous orchid mantises, spikey jungle nymphs, and grotesque giant stick insects. Let’s return to the rainforests of Central and South America to visit with one of the largest cockroaches on Planet Earth, the Central American giant cave cockroach.
Central American giant cave cockroaches are omnivores consuming several types of decaying organic matter.
Harking back to my days in graduate student housing, I had the opportunity to meet my first cockroaches, nasty little rascals called German cockroaches. These disturbing little creatures measured roughly half an inch in length. Now image you turn on the kitchen light at night and see a cockroach ten times the size of the German cockroach skittering across the floor. Well, that’s the size of the Central American giant cave cockroach. This behemoth of the cockroach clan is found in several Central and South American countries as well as many islands in the Caribbean Sea. As its name implies, it is a denizen to limestone caverns and may also be found in the hollows of trees and on the damp, dark floor of tropical forests.
At nearly five inches in length, the Central American giant cave cockroach is one of the largest insects on earth. Wing buds on the back of this nymph foretell its upcoming molt to a winged adult. Bacteria living in the gut of the giant cockroach produce essential amino acids from nutrient-poor decaying plant material consumed by the cockroach. This symbiotic relationship provides home and food for the bacteria and the building blocks of proteins to support growth and development of this giant insect.
This omnivore consumes many kinds of decaying organic matter, but a primary component of its diet is decaying plant material, a notoriously poor source of the important nutrient nitrogen, a key element found in amino acids, the building blocks of proteins. How does this giant of the cockroach world obtain amino acids necessary for growth and development? Through eons of evolution, the giant cave cockroach has formed a symbiotic relationship with a bacterium known as Blattabacterium that makes its home in specialized cells in the gut of the cockroach. These endosymbionts take raw materials like urea and ammonia from food found in the gut of the cockroach and convert these compounds into all the essential amino acids needed for the survival of the giant cave cockroach. This remarkable alliance between a microbe and an insect helps the giant cockroach thrive and repurpose decaying organic matter in the rainforests of the New World.
Wing buds developing on the thorax of this giant cockroach nymph are a sure sign that the molt to winged adult is not far off.
Acknowledgements
We thank Todd Waters for maintaining the Insect Petting Zoo at the University of Maryland and thereby providing the inspiration for this week’s episode. The fascinating article “Genome Sequence of Blattabacterium sp. Strain BGIGA, Endosymbiont of the Blaberus giganteus Cockroach” by C. Y. Huang, Z. L. Sabree, and N. A. Moran provided valuable insights into the mutualism between microbe and cockroach that powered this story.