By Arthur V. Evans
Just kidding. Wood-eating cockroaches have really been here in the Commonwealth all along. But they only eat really rotten wood, so they pose no threat to buildings or furniture. Let’s start at the beginning.
A few years ago, while conducting an insect survey in Shenandoah National Park, I pulled apart a very moist, rotten log to find several shiny black cockroaches over an inch long living in flattened tunnels apparently chewed out of the wood. With chunky, wingless bodies, and thick spiny legs, they resembled somewhat stunted versions of Madagascan hissing cockroaches, popular denizens of insect zoos and the occasional of pet shop.
I recognized these cockroaches immediately as the famous brown-hooded wood cockroach, a native species that has figured prominently in the scientific literature, especially over the last 10 years. Samuel Hubbard Scudder described Cryptocercus punctulatus in 1862 from a single specimen collected right here in Virginia. Draper Valley in Pulaski County, to be exact.
The brown-hooded wood cockroach, Cryptocercus punctulatus Scudder
Scudder was a noted authority not only of grasshoppers, cockroaches, and their relatives, but also of butterflies and fossil insects. He coined the term “Cryptocercus” from the Greek “krypto,” meaning to hide or conceal, and “kerkos,” or tail. This is in reference to the fact that the last three abdominal segments of Cryptocercus are hidden within a chamber created by the seventh abdominal segment.
Cryptocercus cockroaches are no ordinary cockroaches. They takes four to five years to reach maturity, mate for life, reproduce only once in their lifetime and only after they have lived as a couple for a year. Both sexes actively care for their young for up to three years. Most other cockroaches live only two or three years, are quite promiscuous, breed repeatedly, and never see their young, abandoning their eggs before they hatch.
Like termites, adult Cryptocercus chew meandering galleries in rotten logs of both coniferous and hardwood trees. The galleries consist of intersecting tunnels and arena-like chambers in which they raise their young. Females imbed egg cases, or oothecae, in the walls of the tunnels. The larvae, up to as many as 75 in a single brood, change from ivory or golden in color to progressively darker shades of reddish brown as they mature before eventually turning nearly black.
Both parents and offspring eat rotten wood and rely on bacterial and protozoan symbionts in their gut to help them metabolize their food; only termites and Cryptocerus cockroaches harbor these same specific gut symbionts. Since they come into this world without the necessary compliment of gut symbionts, Cryptocercus larvae must obtain them from special anal fluids produced by their parents, just like termites. Up to six cockroach larvae at a time will bury their heads deep within the anal chamber of an adult cockroach to suck up an elixir rich in life-giving bacteria and protozoa.
Young cockroaches grow by molting, or shedding their exoskeletons. As they molt, part of their intestinal lining is also shed, and along with it goes their gut symbionts. After each successful molt they must re-infect themselves by imbibing the anal fluids of their parents in order to metabolize wood and stay alive. By the time they reach their third or fourth larval stage, the young Cryptocercus no longer lose their gut symbionts with each molt and have become nutritionally independent of their parents. Also like termites.
Scientists have long thought that termites were offshoots of ancient cockroaches. Whether Cryptocercus cockroaches are “living fossils” closely related to termites, or a more recently evolved line of cockroach that just happens to share an amazing number of features in common with termites is still hotly debated in the scientific literature.
Scientists eager to explore the interface of population genetics and environment, the key evolutionary forces that drive the development of new adaptations and speciation, find these cockroaches elegant research subjects. After all, they are dependent on a patchy resource (rotten logs), have limited powers of dispersal, and live in close-knit family units. Plus, whether they are primitive or not, the reproductive behavior of Cryptocercus mirrors that of a king and queen termite starting a new colony, which makes them the best living models for studying the development of social behavior in modern termites.
In the 1930’s two additional species of Cryptocercus were discovered in eastern Russia and western China. In 1997, comparative DNA analysis of populations in Appalachia and the Pacific Northwest produced results indicating that each population was actually a distinct species. A similar analysis of the Appalachian populations revealed a complex of four closely related species. One of the new species was named, predictably enough, after Charles Darwin (C. darwini), while another was named in honor of Jerry Garcia (C. garciai) of the Grateful Dead.
Since 1999, an additional five species have been found in East Asia, bringing the total number of species in the world to an even dozen. More species no doubt await discovery by scientists. From Draper Valley, Virginia to China, our understanding of Cryoptocercus and the light they might shed on the very dawn of termites continues to be a long, strange, yet very illuminating trip.
© 2010, A.V. Evans