Salina Woodard '02 searching for wood roaches

Sweet Briar's hardwood forests support an unusual population of wood roaches, Cryptocercus punctulatus Scudder (Blattaria: Cryptocercidae). Don't click away from this page in horror - these roaches, quite different from the german cockroaches that invade houses, are deserving of attention and respect.

In July 2001, an enthusiastic group (R. & C. Ambers, L. Fink, and S. Kellogg) joined North Carolina State University entomologist Dr. Christine Nalepa in searching for wood roaches. In the woods of Paul Mountain not far from the back road, we pried open rotting logs with rock hammers. We discovered not only the roaches, but also a wide variety of other dead wood inhabitants.

Wood roaches are good parents...

     Wood roaches are monogamous and exhibit considerable parental care: a mated pair stay together for several years and raise a single set of offspring. After a sexually mature wood roach finds a mate (how? I don't know), the pair establishes a nesting site in a dead log on the forest floor. They will probably stay in one log for the rest of their lives.

     Wood roaches have ecological and physiological similarities to their close relatives, the termites. Like termites, they feed on dead wood and live in galleries they construct within fallen logs. Since insects lack the enzyme cellulase, they rely on microbes to digest wood. Termites and wood roaches house these microbes, primarily flagellated protozoa, in their gut.

     The mated female lays a clutch of 50-100 eggs. A newly hatched roach nymph's gut is empty - it does not have any symbiotic microbes. To get these from its mother or father it uses proctodeal trophallaxis (feeding on fluids from the adult's anus). The necessity of obtaining gut microbes is a constraint on the life history of the wood roach: these insects cannot grow to maturity as loners. Initially the nymphs feed exclusively by trophallaxis and are completely dependent on their parents for their nutrients. As they mature, they acquire their own gut flora and begin feeding on dead wood directly. Development to sexual maturity takes more than two years.

Click here to view a wood roach adult and a partially obscured nymph.

Why is Dr. Nalepa interested in Sweet Briar's wood roaches?

     Previously thought to be a single species, the eastern wood roach is now proposed by some evolutionary biologists to be a complex of at least four species, identifiable by different numbers of chromosomes and by molecular differences in their mitochondrial DNA. Dr. Nalepa and other scientists have been studying the geographic distribution of these groups.

      C. punctulatus is patchily distributed in the Appalachians. Though not rare in Virginia at altitudes above 3000 ft, few populations are known from low elevations. The Paul Mountain site is at an elevation of less than 900 ft.  Dr. Nalepa collected wood roaches from Sweet Briar to determine their chromosome number and to take morphological measurements. She expects their chromosome number to be the same as a higher elevation population at Mountain Lake Biological Station, but is interested in whether they will share physical characteristics with populations from further south.

Is the future of Sweet Briar's wood roaches secure?

     The wood roaches on Paul Mountain were first located and studied by Dr. Deborah Waller (now at Old Dominion University). We do not know if they occur at other sites on campus.  The Paul Mountain wood roach site was selectively thinned as part of the college's 2001 Forest Management Plan.

     Will the logging affect Sweet Briar's wood roach population? Both Dr. Nalepa and Dr. Waller considered the population to be at risk if selective thinning is undertaken. Dr. Waller was concerned that selective thinning would remove potential logs, especially those of large size, that are their nesting sites and food (D. Waller, email, 19 February 2001). Dr. Nalepa noted that the low altitude Cryptocercus at Sweet Briar "are probably at the limits of their range and therefore fairly sensitive to environmental perturbations. Persistently cool, moist conditions are the most significant factor in keeping a population happy. Opening up the canopy, then, would probably decrease soil moisture levels and allow logs to dry out." (C. Nalepa, email, 15 March 2001)

Are roaches abundant or rare in our forests?

     For her senior research, biology major Salina Woodard '02 sampled other Sweet Briar forests for wood roaches and correlated their abundance with the quality and quantity of coarse woody debris.  She sampled a second site on Paul Mountain, two sites in Fern Woods (on the COSIP transect), and one site each in Williams Creek, Constitution Oaks, Boone-Prior, and Carry Sanctuaries.  She found wood roaches in four of these sites, on Paul Mountain, COSIP, Williams Creek, and Constitution Oaks.  The roaches were not abundant at any individual site, but their wide distribution is reassuring: whether the timbering affects the Paul Mountain population, the three remaining sites are protected within sanctuaries.

Wood roaches are not the only inhabitants of dead logs that show parental care.

In addition to several dozen roaches our hunt within rotting logs uncovered the following

• A female centipede curled protectively around a mass of transparent baby centipedes. In many centipedes the females guard her eggs and newly hatched offspring. Since I had never seen this before I collected the group alive, to watch the maternal behavior in the lab. This disturbance was too great. When I checked the group later in the day, only one baby remained, and I assume that the mother cannibalized her young.
  

• Passalid beetle adults and immatures. These large beetles (adults are about 1-1/2 inches long) live in family groups in decaying logs and have considerable social behavior (Schuster and Schuster 1985). Like the wood roaches they are monogamous. Adults defend their young and provide them with macerated wood pulp. Apparently passalids do not have gut protozoa to digest cellulose, but as fungi and other microbes decompose the macerated pulp and feces they make nutrients available to the larvae.

  Both adult and larval passalids produce squeaking sounds when disturbed, and a large number of distinct acoustical signals have been identified.

  Only one passalid species occurs in the eastern United States, Odontotaenius disjunctus (Illiger) (formerly Passalus cornutus Fabricius and Popilius disjunctus Ill.).

• Many logs contained colonies of carpenter ants and of termites.

Why is parental care so widespread among the arthropods that live and feed in fallen logs?