Blattodea (cockroaches)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Phylum: Arthopoda > Mandibulata > Atelocerata > Panhexapoda > Hexapoda > Insecta (insects) > Dicondyla > Pterygota > Metapterygota > Neoptera > Polyneoptera > Dictyoptera

Introduction

Cockroaches could be confused with members of the order Orthoptera (crickets and grasshoppers) but they do not have well-developed hindlegs for jumping. Most cockroaches, such as the American Cockroach, lay their eggs in a brown oblong case called an ootheca and in many species these are carried around by the female for some time before being deposited on the ground. The Cape Mountain Cockroach has an interesting biology in that the eggs mature and hatch inside the female so that she 'gives birth' to young. In this species the male is winged and the female wingless (hence the generic name meaning 'without wings'). Cockroaches are mainly nocturnal and by day hide in dark places such as under rocks, dead wood and bark. They are mainly scavengers, feeding on dead organic matter such as plant matter.

Origins

Fossil cockroaches have been recorded in deposits dated to as far back as the Upper Carboniferous, about 305 million years ago. During the Carboniferous they were one of the most abundant of the insect orders in terms of number of individuals. Apterygote insect orders Collembola and Archaeognatha were already present as were aquatic orders such as Odonata (dragonflies) and Ephemeroptera (Mayflies). There were also a number of insect orders present that are now extinct. The Orthoptera (crickets, etc) also go back to the Carboniferous but the largest present day insect orders such as Coleoptera (beetles), Diptera (flies), Hemiptera (bugs) and Lepidoptera (moths and butterflies) had not yet evolved.

General life cycle

Adults. Depending on species, adult cockroaches can range in size from 3 mm to at least 65 mm long. Cockroaches are flattened in appearance which enables them to crawl into narrow crevices. In some species males and females look superficially similar but in others the adult females are winged and the adult males wingless.

Eggs. Eggs are usually laid in a packet called an ootheca. The ootheca is formed in the female and as it exits it is stamped into shape by the ovipositor valves (rather like a snackwich maker gives toasted bread those troughs and ridges), and hardens on being exposed to air. The shape of the ootheca is often species specific. The female carries the ootheca round on the end of her abdomen for varying lengths of time before dropping it on the ground or glueing it to something. After depositing it, females of some species cover the ootheca with debris so that it is difficult for it to be located by predators and parasitoids. In some species females carry around the ootheca for the entire embryonic development. Although the majority of cockroach species are oviparous in that they lay their eggs externally (in oothecae), there are some in which egg development is internal. Internal egg development can be divided into three main categories.

False ovoviviparity. The ootheca is produced inside the female but instead of being laid, it is retained in a uterus or brood sac where the eggs develop. This is the main form of reproduction in the family Blaberidae but has also been recorded rarely in the Blatellidae.
True ovoviviparity. This form of reproduction is different from false ovoviviparity in that an ootheca is not formed. Instead, eggs pass from the oviducts into the uterus where they lie in no particular order and undergo embryonic development.
Viviparity. Viviparity is only known in the genus Diploptera. The eggs are small and have insufficient water and yolk to complete development. They are kept inside the uterus within an incomplete oothecal membrane and their embryos absorb water and disolved proteins and carbohydrates that are produced by the uterus.

Nymphs. Being hemimetabolous, the nymphs are similar in general shape to the adults but are smaller, lack wings and genitalia are undeveloped. They hatch more-or-less simultaneously from the ootheca by swallowing air and inflating themselves, in this way splitting open the two halves. They pass through a series of moults before reaching the adult stage.

Natural enemies

Evaniid wasps parasitise oothecae.
Beetles in the subfamily Rhipidiinae of the family Rhipiphoridae parasitise cockroach nymphs.
Predators of cockroaches are many ranging from invertebrates such as ants through to vertebrates such insectivorous frogs, reptiles, birds and mammals. Cockroaches protect themselves from predators mainly by hiding away, but produce defensive secretions if attacked. These secretions can also render them distasteful.
Internal parasites include amoebae, ciliates, nematodes and Nematomorpha.

Economic importance

The vast majority of cockroach species (more than 99% of them) live in the wild and are of no economic importance. However, there are a few species that thrive in and around human habitations. They are pests because they destroy food and contaminate it with their smelly excreta. They can also eat book labels and bindings. The most common pest cockroach in South Africa is the American Cockroach Periplaneta americana. The smaller German Cockroach Blattella germanica can also be encountered indoors, and on the subtropical coast (e.g. in Durban) one can encounter the large Indian Cockroach Blatta orientalis.

Classification

Superfamily: Blattoidea
	Family: Blattidae Thirty-four species recorded from southern Africa. Periplaneta americana (American cockroach) and Blatta orientalis (Oriental cockroach) are introduced species to the region.
	Family: Cryptoceridae Not found in southern Africa
Superfamily: Blaberoidea
	Family: Polyphagidae
	Family: Blattellidae Includes Blatella germanica (German Cockroach).
	Family: Nocticolidae
	Family: Blaberidae Includes Aptera fusca (Cape Mountain Cockroach)

Further easy reading

Skaife, S.H. 1979. African Insect Life. Struik, Cape Town, pp. 42-46.

Key scientific publications on cockroaches

Bell, W. J., and K. G. Adiyodi. 1981. The American Cockroach. Chapman & Hall, New York.
Cornwell, P.B. 1968. The cockroach. 2 volumes. Hutchinson and Co., London.
Grandcolas, P. 1996. The phylogeny of cockroach families: a cladistic appraisal of morpho-anatomical data. Canadian Journal of Zoology 74: 508-527.
Guthrie, D.M. & Tindall, A.R. 1968. The biology of the cockroach. Edward Arnold, London.
Marshall, J. 1985. Order Blattodea. In: Insects of southern Africa (eds C.H. Scholtz & E. Holm). Butterworths, Durban, pp. 49-52.
McKittrick, F.A. 1964. Evolutionary studies of cockroaches. Memoir of the Cornell University Agricultural Experimental Station 389: 1-197.
Princis, K.1963. Revision der südafrikanische Blattarienfauna. In: South African Animal Life Vol. 9 (Eds Hanstrom, B., Brinck, P. & Rudebeck, G.). Almqvist Wiksell, Stockholm, pp 9-318.
Roach, A.M.E. & Rentz, D.C.F. 1998. Blattodea. Zoological Catalogue of Australia 23: 21-162. Appendix of nomenclatural decisions and taxonomic index on pages 400 and 407-426.
Roth, L.M. 1970. Evolution and taxonomic significance of reproduction in Blattaria. Annual Review of Entomology 15: 75-96.
Roth, L.M. 1991. Blattodea. In: The insects of Australia. 2nd edition Volume 1. Melbourne University Press, Melbourne, pp. 320-329.
Roth, L.M. & Willis, E.R. 1957. The medical and veterinary importance of cockroaches. Smithsonian Miscellaneous Collections 134 (10): 1-147 (reprinted 1967, Edwards Brothers Inc., Ann Arbor, Michigan).
Roth, L.M., & Willis, E.R. 1960. The biotic associations of cockroaches. Smithsonian Misc. Collect. 141:1-470.
Schal, C., Gautier, J.-Y. & Bell, W.J. 1984. Behavioural ecology of cockroaches. Biological Reviews 59: 209-254.
Thorne, B. L., and J. M. Carpenter. 1992. Phylogeny of the Dictyoptera. Systematic Entomology 17:253-268.