In the introduction to his book "The Cockroach Vol.1" P.B.Cornwell's opening sentence is . "The Cockroach is probably the most obnoxious insect known to man." This is obviously the statement of a man who has spent too much time studying those few species of Blattodea which have so much in common with mankind that they have chosen to live with us.
There are nearly 4,000 species of Cockroaches (Dictyoptera, Blattodea) in the world, of which only 25 to 30 (or less than 1%) have any pest status, the rest are innocent members of the Earth's fauna, some of which are clean living, non-aggressive and slow moving, and as such make great pets. The largest known Cockroaches in the world are (largest wingspan up to 18 cm) Megaloblatta longipennis, largest body, Macropanesthia rhinocerus from Australia weighing in at up to 50 grams. The smallest known is Attaphilla fungicola which lives in the nests of Leaf Cutter ants of the genus Atta in North America and feeds on the fungus they farm, it is about 4 mm long.
Cockroaches have been on the Earth for at least 250 million years and it is possible that in the late carboniferous cockroaches out numbered (in terms of number of individuals) all other flying insects. Most Cockroaches are tropical in habitat and Britain has only 3 native species, which is less than the number of introduced species. Many Cockroaches are diurnal, though most are nocturnal. Many are forest floor species though some are cave dwellers, some are semi-aquatic, some burrowing, some wood boring, and some even make their homes in the nests of social insects (Attaphila fungicola in the nests of various Attine ants).
Cockroaches are related to Termites (Isoptera) which some authorities believe arose 70 to 50 million years ago as an offshoot (or possibly 2 offshoots) of the Cockroach lineage of the time. Two pieces of evidence supporting this are:- 1) the fact that Termites are Eusocial insects and some species of Cockroach are primitively subsocial, and 2) the gut microflora of the primitive wood eating Cockroaches (such as Cryptocercus punctulatus) are very similar to that of the Termites. Modern Cockroaches are more similar to their ancient fossil ancestors than any other extant (still living) insect.
A hemimetabolous insect with an oval somewhat flattened head partially concealed by the pronotum and with the mouth pointing backwards between the fore coxa.
The antennae are filiform (long and thin) and inserted below the middle of the eyes, the mouthparts are adapted for biting, chewing and licking while the compound eyes are usually large and irregularly hemispherical being wider near the vertex (the top of the front of the head). The forewings (tegmina) are usually hardened and often opaque, the hind wings are membranous. (In Cockroaches, except very small ones, the wings, in those species which have them overlap in the middle of the abdomen whereas the wings of beetles never overlap at all). The legs are almost equal in length and depressed beneath the body. The abdomen has ten segments but only 7 or 8 visible from above while from beneath 9 plates (sternites) are visible in the male but only 7 in the female. Males and nymphs carry 2 smaller appendages thinner than and below the cerci (singular cercus) called 'styles'.
The eggs are laid in an ootheca (natures answer to the polystyrene egg box). Some species will secrete these in the corners of the cage or other accessible nooks and crannies while others will carry the ootheca around with them, either inside or partly extruded from the body until it is time for the young to hatch. Some species are parthenogenetic ( i.e. the females give birth to other females which give birth to other females which, etc. etc... and no males are ever seen) i.e. Pycnoscelus surinamensis
The Oothecae contain 14 to 28 eggs. Incubation time for the eggs is temperature dependant and hatching takes approximately 35 days at 30 degrees C and 59 days at 20 degrees C. Incubation time is more temperature dependant for Periplaneta americana than for any other species of Cockroach so far studied. Nymphs take between 4.5 and 15 months or longer to reach maturity depending on the temperature and the availability of food, females normally undergo 9 moults while males normally take 13. Life expectancy ranges from 2 to 4 years and a female can produce 30 oothecae resulting in 1000 young before dying of old age.
Virgin females are known to produce sex attractants in P.americana and some other species, these can attract a male in as small amounts as times 10 to the minus 14 micrograms. Courtship involves antennal sparring and the male raising and fluttering his wings. The female then feeds on the secretions of the males dorsal glands (situated on the upper surface of his abdomen). Following this the male moves backwards under the female until he is able to clasp her genitalia from beneath, once contact is assured the two assume the more familiar end to end position, mating normally lasts about one hour.
Pycnoscelus surinamensis is not only parthenogenetic, and thus has no courtship or sex, but is also ovoviviparous meaning that the ootheca is first extruded and then brought back into the females brood pouch for incubation.
Apart from Mankind Cockroaches are eaten by a wide range of small mammals, birds, reptiles and amphibians. The Cockroach mite Pimeliaphilus cuniliffei feeds on all Cockroach life stages and can cause considerable damage to infested populations. Parasites include all the Evaniidae (see Evaniidae Research for more info) i.e. Evania appendigaster (Evanidae) on the oothecae of P. americana and P. australasiae, Tetrastichus hagenowi (Eulophidae) on P. americana, Syntomosphyrum blattae (Eulophidae) and Systellogaster ovivora (Pteromalidae) on Parcoblatta pensylvanica and several solitary wasps such as Ampulex compressa, Podium cardina and Podium rufipes.
Mankind's long relationship with Cockroaches probably began with the Cockroaches as food items, but the relationship really took off when Humans started storing food for the winter and continued to improve the better we became at creating artificially stable habitats with plenty of food.
Ships were particularly prone to experiencing outbreaks of plague proportions partly because they represented a predator free habitat. In 1634 Moffut in the first entomology book printed in Britain records that Drake reported that the Phillip, which he had just captured, was overrun with 'roaches, and in 1792 Captain Bligh was so determined to reduce the Cockroach numbers that he disinfected the Bounty with boiling water.
Cockroaches are not associated with disease the way Fleas or Mosquitos are (i.e. by means of direct transmission), instead because they tend to inhabit those uncleanable areas of any establishment they inadvertently come into contact the microbial agents of decay, they inevitably bring some of these with them when they come to visit our food supplies, thus contaminating them with often pathogenic organisms which subsequently cause disease.
The word Cockroach possibly come from the Spanish 'Cucaracha'. Like all creatures that bring themselves regularly to Mankind's attention Cockroaches have acquired a large number of common names, such as 'lucifaga' because of their habitat of fleeing the light. In Sweden they were known as 'Brotaetare' or 'Bread Eaters', In the U.K. the various pest species have been called 'Steambug', 'Steamfly' and 'Shiner'. In America they are known as 'Yankee Settlers', 'Croton Bugs' or 'Bombay Canaries' depending on where you are. More humorously Blattella germanica known as the 'German Cockroach' here is known as the 'Russian Cockroach' or the 'French Cockroach' in different parts of Germany and as the 'Prussian Cockroach' in Russia, while the 'American Cockroach' Periplaneta americana and the 'Australian Cockroach' Periplaneta australasiae both probably originated in Africa and not in the countries indicated by their common names.
The Blattodea are an homogeneous group containing 4 families.
Thanks to Rob Lind for donating the images denoted by **.
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