Wood Roach

Cryptocercus punctulatus
Thursday, July 28, 2011

           This insect, also called the brown-hooded cockroach, is related most closely to cockroaches and termites. C. punctulatus was previously thought to be the only species in the Cryptocercus genus occurring in the Eastern United States—three other species are recognized worldwide. However, recent genetic work suggests the presence of four separate evolutionary lineages in the Eastern US which may be impossible to tell apart without examining their DNA sequence and chromosome number.

            At any event, all wood roaches in the genus Cryptocercus occurring near here have the same outward characteristics. Unusually among roaches of any sort, C. punctulatus have no wings at all. The males and females are of the same appearance and size —usually 23-30 mm long. They are described as having a dark brown or black coloration, and are more elongated in shape than many other roaches. One identifying characteristic is the distinctly raised forward margin of the pronotum (the segment directly behind the head). This partially covers the top of the head and is thought to protect the head while they are burrowing. They are impossible to mistake—C. punctulatus is the only wingless roach in this area.

           These roaches are actually quite unique in their behavior. Once sexually mature, males and females will locate each other and find a suitable log on the forest floor to settle down in. They will probably stay in that log for the rest of their lives. Similar to termites, wood roaches feed on rotting wood and construct galleries in dead trees. Once they have mated, the female will lay a clutch of 50-100 eggs inside their log. The mated pair will stay together for several years within the same log and raise a single brood of offspring together. Although they are not the only invertebrate to display parental care, the degree to which they are committed to their offspring is unusual.

            Another interesting aspect of a wood roach’s behavior has to do with their digestive tract. Wood roaches, like humans, are physically incapable of digesting cellulose. For a species which lives solely by consuming rotten wood, this presents quite a dilemma. However, wood roaches, like cows, harbor a multitude of cellulose-digesting symbiotic microbes in their gut which help convert cellulose into a digestible sugar, such as dextrose. When a roach nymph is newly hatched from the egg (above right), it harbors none of those essential microbes necessary to the digestion of wood. They obtain those microbes through a process called proctodeal trophallaxis (feeding on fluids from the adult’s anus). Thus, nymphs could never survive without the presence of an adult.

            C. punctulatus can be found in disjunct areas throughout North America. They occur in the mountainous regions of Oregon and northern California, as well as in the Appalachian Mountains. They can be typically found within any rotting, moist hardwood or softwood log. They are not considered a pest to humans, as many of their relatives are, because they rarely enter human dwellings. Extensive research has been done on this species at MLBS by Dr. Christine Nalepa.

Hazel Galloway