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Cockroaches could be confused with members of the order Orthoptera (crickets and
grasshoppers) but they do not have well-developed hindlegs for jumping. Most
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.
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
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,
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
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.
species recorded from southern Africa.
Periplaneta americana (American
cockroach) and Blatta
orientalis (Oriental cockroach) are introduced species to the region.
Not found in
Includes Blatella germanica
Includes Aptera fusca
(Cape Mountain Cockroach)
Further easy reading
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:
Thorne, B. L., and J. M. Carpenter. 1992. Phylogeny of the
Dictyoptera. Systematic Entomology 17:253-268.
Cockroach homepage Includes a
useful bibliography of scientific publications on cockroaches.
Blattodea page. Useful page which includes some of the key publications on cochroaches as well
as links to other sites.
Text by Hamish G. Robertson