Cockroaches

Cockroaches belong to the Phylum Arthropoda, Subphylum Labiata, Superclass Hexapoda, Class Insecta, and Order Blattodea. The order includes approximately 4,600 species in almost 500 genera and seven families. Very likely at least twice this number remains to be discovered and described worldwide. Some of the most well-known cockroach examples are two pest species belonging to the family Blattidae: the American cockroach (Periplaneta americana) and German cockroach (Blattella germanica). Cockroaches are considered one of the most successful groups of invertebrates because of their adaptability in various environmental conditions and occupy a very wide range of habitats from caves to mountains to rainforests to deserts. As a group, cockroaches also exhibit a remarkable diversity of form, coloration, size, and behavior. Although no list of types of cockroaches in Arkansas has been published, four species within two families are common in the state.

In the past, cockroaches were considered to be part of the Order Orthoptera (crickets and grasshoppers) but have since been classified as a separate order. Recent cladistical analyses suggest the mantids to be the sister group to Blattodea. The wood roaches or brown-hooded cockroaches (Cryptocercus spp.) also share characteristics such as species of gut bacteria with the termites. The cockroach families Lamproblattidae and Tryonicidae are placed within the superfamily Blattoidea. Previously, the families Corydiidae and Ectobiidae were known as the Polyphagidae and Blattellidae, respectively.

The earliest cockroach-like fossils are from the Carboniferous period 354 to 295 million years ago. However, these fossils show insects unlike modern cockroaches in having long external ovipositors and are considered the ancestors of mantises, as well as modern blattodeans. Modern cockroaches radiated from them by the middle of the Mesozoic. A common European and African cockroach may have gotten its evolutionary start in North America, according to new fossil findings.

Cockroaches are cosmopolitan, with each continent supporting its own indigenous taxa. Most of these include omnivores or detritivores that live in a range of habitats such as among warm and humid leaf litter, in rotting wood, in thick vegetation, in crevices, in cavities beneath bark, under logs, and among debris. Some roaches are arboreal, some live in caves, and some are aquatic. A small number of species have been transported around the world by human activity, resulting in them living in close proximity to humans in buildings; they are generally regarded as ugly pests.

Though considered tropical insects, cockroaches can flourish in any environment where there is sufficient food and warmth. Most North American cockroach species live in woodlands and are not pests. Those found indoors may be anthropophilic “pest” species or those that migrate inside inadvertently. Of species found indoors, German cockroaches are commonly found in homes throughout the world.

Adult cockroaches are small to large insects, 3.0 to 80 mm (0.1 to 3.1 in.) in length. The world’s heaviest cockroach is the wingless Australian rhinoceros cockroach (Macropanesthia rhinoceros), which weighs up to 35 g (1.2 oz.) and has a body length of up to 8 cm (3.1 in.). It is among the longest lived of all insects with a lifespan of more than ten years. The species with the greatest wingspan is the Central and South American Megaloblatta blaberoides, which has a spread of up to 185 mm (7.3 in.).

Cockroaches possess a flattened dorsolaterally body that is roughly oval and has a shield-like plate called the pronotum, which covers its thorax and posterior region of the head. The antennae are long, slender, and many-segmented, and their mouthparts are adapted for chewing. Not all species have wings, but when wings are present, the forewings are normally leathery and the hind wings thin and fan-like membranous. The coxae of the legs are flattened to enable the femurs to fit precisely against them when folded.

Some behavioral characteristics of roaches include: (1) response to contact or touch (thigmotaxis), (2) allogrooming, (3) substrate manipulation, (4) hygienic behavior, (5) food sharing, (6) cannibalism, (7) excretion behavior, (8) vibrational communication, (9) kin recognition, (10) trail following, (11) burrowing, (12) care of the brood, (13) cropping of antennae, and (14) certain mating behaviors.

Cockroaches are not considered eusocial because their populations are not divided into different caste systems; however, they are still social insects and can live in groups with over a million individuals. During the evolution of eusociality, the individuals need to share a desire to group together. Juvenile cockroaches have a tendency to amass, while adults often compete aggressively with each other for space and resources. Allogrooming is not a behavior generally engaged in by most cockroaches, although individuals groom themselves. An exception to this is the cockroach Cryptocercus, which seems to be more closely related to the termites than to other cockroaches. Here, juveniles groom each other and also groom adults.

Cockroaches are nocturnal, only foraging for food and water during the night. They engage in the consumption of fecal pellets or coprophagy. However, young cockroaches are feeble as foragers, as they seldom stray from their hiding places, and obtain much of their sustenance from eating the fecal pellets of larger individuals. From this nutrition they acquire the microbial flora that help them to digest their food. Although some species harbor these symbionts in their guts, which facilitate cellulose digestion, many species also produce enzymes to digest cellulose independent of the symbionts.

A single family, the Cryptocercidae, shares such characteristics as the segmental origin of certain female reproductive structures and the depositing of eggs in the oothecae that are typical of cockroaches. Some other interesting cockroaches include the Madeira cockroach (Rhyparobia maderae), which can stridulate, making a shrill voice by rubbing body parts together, an unusual ability for a roach; when threatened by predators it also gives off an offensive odor. The smallest cockroach at 3 mm (0.1 in.) is Attaphila fungicola, which inhabits an ecological niche living as myrmecophiles in the nests of leaf-cutting ants, where they are reported to feed on the fungus their host ant farm, or on the cuticular lipids of ant workers. Another species of interest is the giant cave cockroach, Blaberus giganteus, of Central and northern South America and some Caribbean islands, which feeds on bat guano.

In terms of reproduction and their life cycle, cockroaches undergo incomplete metamorphosis, termed hemimetabolous; there is no pupal stage, and the nymphs resemble the adults, apart from their size and the absence of wings. One species, the Surinam cockroach (Pycnoscelus surinamensis), is parthenogenic, but males are found in all other species that have been studied. Female cockroaches produce a hardened egg case known as an oothecal, and, depending upon the species, it can hold anywhere from ten to fifty eggs. Most commonly this structure is carried by the female; in some species, the ootheca may be carried inside the abdomen and not be visible. Most species of cockroach have little parenting behavior once eggs hatch from the oothecae. However, some species show a significant amount of parental care. For example, in some species, the nymphs are carried on the back (underneath the wings) of the female cockroach, and they feed on liquid secretions from pores on her back and even by piercing the membrane between her abdominal plates and feeding on the hemolymph (insect blood) coming from the wound. In the majority of species, growth to maturity takes three to four months, but in a few species, the nymphal stage can last for several years. The main factors affecting the duration of this stage are seasonal differences, and the amount of nutrients gained from the diet. In some species, and warmer environmental conditions, adulthood is reached within 600 days, but in cooler climates it can take over a year. However, many cockroach species are reasonably long-lived and commonly kept as pet species, such as the Madagascan hissing cockroach (Gromphadorhina portentosa), which forces air through their spiracles to produce a hissing sound. These cockroaches may live for up to three years.

The various factors that structure the communities of cockroaches are not well understood. As generalist feeders, their populations may be limited by the effects of predators, parasites, and parasitoids rather than lack of nutrients. Cannibalism is reported to be common, although the situations under which this odd behavior occurs are also not clear. Several interesting invertebrates feed on cockroaches, including ensign wasps. They are commonly found around homes with cockroach infestations. These wasps search out ootheca of cockroaches. Once these are located, the wasps lay their own eggs within the capsule. When the ensign wasps hatch, they consume the developing cockroaches. Horsehair worms (nematomorpha) also develop inside cockroaches, living off the hemolymph as the insect grows. Once it reaches adulthood, the worm is capable of changing the cockroach’s behavior, forcing it into water, where the cockroach will commit suicide and drown, allowing the horsehair worm to free itself from the roach’s body and continue its unique life cycle.

As in most insects, cockroaches are able to communicate with each another by releasing pheromones. It has also been documented that cockroaches release hydrocarbons from their body that are transferred through interactions of their antennae. These chemical compounds can aid in cockroach communication and even affirm whether an individual is a member of its kin group or not to prevent inbreeding of such. In lab experiments, cockroaches that have been isolated have shown extreme behavioral effects and are less stimulated by these hydrocarbons and pheromones, possibly suggesting a group environment is required for development of these communication skills.

As intermediate hosts of parasites, cockroaches have been recognized as mechanical vectors of pathogens that can infect/infest humans or animals. Several genera of parasites have been identified as being associated with cockroaches, including nematodes (Ascaris, Enterobius, Trichuris, Toxocara, hookworms) and coccidians (Eimeria). Most of these are recognized as responsible of zoonosis and, accordingly, can be released in environments by hosts and easily disseminated by cockroaches as mechanical vectors. Therefore, intimate contact with cockroaches, especially in human dwellings, should be discouraged.

Interestingly, the acanthocephalan (Moniliformis moniliformis), an endoparasite found in the American cockroach (P. americana), has been shown to experience a decrease in several behaviors in laboratory experiments using infected cockroaches. These include wind-evoked escape responses, predator avoidance behavior (which consisted of fewer escape responses), longer latency, and higher threshold for escape behavior.

As of 2020, there is no published list of cockroach species that occur in Arkansas. Four species within two families, however, are quite common in Arkansas: Oriental (Blatta orientalis) and American cockroaches (Blattidae), German cockroaches (Ectobiidae), and brown-banded cockroaches (Ectobiidae).

For additional information:
Allen, R. T. “The Oldest Dead Cockroach: Fossils—Our Link to Ancient Arkansas History.” Arkansas Naturalist 1 (1983): 1‒4.

Atkinson T. H., P. G. Koehler, and R. S. Patterson. “Catalog and Atlas of the Cockroaches (Dictyoptera) of North America North of Mexico.” Miscellaneous Publications of the Entomological Society of America 78 (1991): 1‒86.

———. “Where the Roaches Are. The Geography of U.S. Cockroaches.” Pest Control 59 (1991): 36‒40.

Camhi, J. M., and T. G. Nolen. “Properties of the Escape System of Cockroaches during Walking.” Journal of Comparative Physiology A 142 (1981): 339‒346.

Chan, O. T. M., E. K. W. Lee, J. M. Hardman, and J. J. Navin “The Cockroach as a Host for Trichinella and Enterobius vermicularis: Implications for Public Health.” Hawaii Medical Journal 63 (2004): 74–77.

Djernæs, M., Klaus-Dieter Klass, Mike D. Picker, and Jakob Damgaard. “Phylogeny of Cockroaches (Insecta, Dictyoptera, Blattodea), with Placement of Aberrant Taxa and Exploration of Out-Group Sampling.” Systematic Entomology 37 (2011): 65–83.

El-Sherbini, G. T., and M. R. Gneidy. “The Role of Cockroaches and Flies in Mechanical Transmission of Medical Important Parasites.” Journal of Entomology and Nematology 3 (2011): 98–104.

Fotedar, R., E. Nayar, and J. C. Samantray, et al. “Cockroaches as Vectors of Pathogenic Bacteria.” Journal of Communicable Diseases 21 (1989): 318–322.

Gotelli, N. J., and Janice Moore. “Altered Host Behaviour in a Cockroach-Acanthocephalan Association.” Animal Behavior 43 (1992): 949‒959.

Graczyk, T. K., R. Knight, and L. Tamang. “Mechanical Transmission of Human Protozoan Parasites by Insects.” Clinical Microbiology Reviews 18 (2005): 128–132.

Inward, Daegan, George Beccaloni, and Paul Eggleton. “Death of an Order: A Comprehensive Molecular Phylogenetic Study Confirms that Termites are Eusocial Cockroaches.” Biology Letters 3 (2007): 331–335.

Libersat, F., and Janice Moore. “The Parasite Moniliformis Alters the Escape Behavior Response in Its Cockroach Host Periplaneta americana.” Journal of Insect Behavior 13 (2000): 103‒110.

Park, Yung Chul, Philippe Grandcolas, and Jae Chun Choe. “Colony Composition, Social Behavior and Some Ecological Characteristics of the Korean Wood-Feeding Cockroach (Cryptocercus kyebangensis).” Zoological Science 19 (2002): 1133–1139.

Slaytor, Michael. “Cellulose Digestion in Termites and Cockroaches: What Role Do Symbionts Play?” Comparative Biochemistry and Physiology B 103 (1992): 775–784.

Chris T. McAllister
Eastern Oklahoma State College