Among the most well-known species are the American cockroach,
Periplaneta americana, which is about 3 cm long, the German
cockroach, Blattella germanica, about 1½ cm long, the Asian
cockroach, Blattella asahinai, also about 1½ cm in length, and
the Oriental cockroach, Blatta orientalis, about 2½ cm. Tropical
cockroaches are often much bigger, and extinct cockroach
relatives such as the Carboniferous Archimylacris and the
Permian Apthoroblattina were several times as large as these.
When infesting buildings, cockroaches are considered pests; out
of the thousands of species, however, only about 30 (less than
1%) fall into this designation.
The earliest cockroach-like fossils are from the Carboniferous period between 354–295 million years ago. However, these fossils differ from modern cockroaches in having long ovipositors and are the ancestors of mantids as well as modern cockroaches. The first fossils of modern cockroaches with internal ovipositors appear in the early Cretaceous.
Mantodea, Isoptera, and Blattodea are usually combined by entomologists into a higher group called Dictyoptera. Current evidence strongly suggests that termites have evolved directly from true cockroaches. If this is the case, then Blattodea excluding Isoptera is not a monophyletic group and the Isoptera are actually a family (or epifamily) of cockroaches.
Cockroaches are generally omnivores. An exception to this is the wood-eating Cryptocercus species found in Russia, China, Korea and the United States. Although they are incapable of digesting the cellulose themselves, they have a symbiotic relationship with a protozoan that digests the cellulose, allowing them to extract the nutrients. In this, they are similar to termites and current research suggests that the genus Cryptocercus is more closely related to termites than it is to other cockroaches. Cockroaches are most common in tropical and subtropical climates. Some species are in close association with human dwellings and widely found around garbage or in the kitchen.
Cockroaches, like all insects, breathe through a system of tubes called tracheae, a word similar to the name of the tube leading to the lungs in mammals. The tracheae of insects are attached to the spiracles which are small valved openings on the side of each body segment, excluding the head. Thus the cockroach can breathe without its head. The valves open when the CO2 level in the insect rises to an unacceptable level; then the CO2 diffuses out of the tracheae to the outside and fresh oxygen diffuses in. The tracheal system brings the air directly to cells because they branch continually like a tree until their finest divisions tracheoles are associated with each cell allowing gaseous oxygen to dissolve in the cytoplasm lying across the fine cuticle lining of the tracheole. CO2 diffuses out of the cell into the tracheole.
Most insects do not have muscular lungs and thus do not actively breathe in the vertebrate lung manner. However, in some very large insects the diffusion process may not be sufficient to provide oxygen at the necessary rate and body musculature may contract rhythmically to forcibly move air out and in the spiracles and one can actually call this breathing. This might be associated with such activities as the energetic flight of the migratory locust.
Consequently, cockroaches can survive decapitation for a very long period to human standards, but of course become unable to fend for themselves and eventually die.
Female cockroaches are sometimes seen carrying egg cases on the end of their abdomen; the egg case of the German cockroach holds about 30–40 long, thin eggs, packed like frankfurters in the case called an ootheca. The eggs hatch from the combined pressure of the hatchlings gulping air and are initially bright white nymphs that continue inflating themselves with air and harden and darken within about four hours. Their transient white stage while hatching and later while molting has led to many individuals to claim to have seen albino cockroaches.
Common household roaches A. German cockroach, B. American cockroach, C. Australian cockroach, D&E. Oriental cockroach (♀ & ♂)A female German cockroach carries an egg capsule containing around 40 eggs. She drops the capsule prior to hatching. Development from eggs to adults takes 3-4 months. Cockroaches live up to a year. The female may produce up to eight egg cases in a lifetime; in favorable conditions, it can produce 300-400 offspring. Other species of cockroach, however, can produce an extremely high number of eggs in a lifetime. Laying up to 100 eggs in each egg sac, it only needs to be impregnated once to be able to lay eggs for the rest of its life.
The world's largest cockroach is the Australian giant burrowing cockroach, which can grow to 9 cm in length and weigh more than 30 grams. Comparable in size is the giant cockroach Blaberus giganteus, which grows to a similar length but is not as heavy.
Cockroaches are mainly nocturnal and will run away when exposed to light. A peculiar exception is the Oriental cockroach, which is attracted to light.
The cockroach is also one of the hardiest insects on the planet, capable of living for a month without food; being able to survive even on the glue from the back of postage stamps. It can also hold its breath for 45 minutes and has the ability to slow down its heart rate.
Ootheca of Periplaneta americana; Florianópolis, SC, BrasilIt is popularly suggested that cockroaches will "inherit the earth" if humanity destroys itself in a nuclear war. Cockroaches do indeed have a much higher radiation resistance than vertebrates, with the lethal dose perhaps 6 to 15 times that for humans. However, they are not exceptionally radiation-resistant compared to other insects, such as the fruit fly .
The cockroach's ability to withstand radiation better than human beings can be explained in terms of the cell cycle. Cells are more vulnerable to effects of radiation when they are dividing. A cockroach's cells divide only once when in its molting cycle, which at most happens weekly. The cells of the cockroach take roughly 48 hours to complete a molting cycle, which would give time enough for radiation to affect it but not all cockroaches would be molting at the same time. This would mean some would be unaffected by the initial radiation and thus survive, at least until the fallout arrived.
Cockroaches have been shown to exhibit emergent behavior.
Research being conducted at the University of Florida shows that cockroaches leave chemical trails in their feces. Other cockroaches will follow these trails to discover sources of food and water, and also discover where other cockroaches are hiding. One of the major implications of this research is a new technique in cockroach pest control. Cockroaches could potentially be removed from a home by leaving a chemical trail that leads away from the home.
Research has shown that group-based decision making is responsible for more complex behavior such as resource allocation. A study where 50 cockroaches were placed in a dish with three shelters with a capacity for 40 insects in each, the insects arranged themselves in two shelters with 25 insects in each, leaving the third shelter empty. When the capacity of the shelters was increased to more than 50 insects per shelter, all of the cockroaches arranged themselves in one shelter. Researchers found a balance between cooperation and competition exists in group decision-making behavior found in cockroaches. The models used in this research can also explain the group dynamics of other insects and animals.
A 2005 US national study on factors that affect asthma in inner-city children shows that cockroach allergens appear to worsen asthma symptoms more than other known triggers. This study, funded by the US National Institute of Environmental Health Sciences (NIEHS) and the US National Institute of Allergy and Infectious Diseases (NIAID), is the first large-scale study to rank asthma triggers according to severity.
Additionally, a 2005 research study, sponsored by the National Pest Management Association (NPMA), shows a disparity in homeowner knowledge about this link. Only 10% of homeowners nationwide feel that cockroaches are a threat to their family's health.
Cockroaches live in a wide range of environments around the world. Pest species of cockroaches adapt readily to a variety of environments, but prefer warm conditions such as found within buildings. Many tropical species prefer even warmer environments and do not fare well in the average household. Only about 20 species of cockroaches out of the 3,500 are suited to thrive in the typical home.
There are numerous parasites and predators of cockroaches, but few of them have proven to be highly effective for biological control. Wasps in the family Evaniidae are perhaps the most effective insect predators, as they attack the egg cases, and wasps in the family Ampulicidae are predators on adult and nymphal cockroaches (e.g., Ampulex compressa). The house centipede, however, is probably the most effective control agent of cockroaches, though most homeowners find the centipedes themselves objectionable. Preventative measures include keeping all food stored away in sealed containers, using garbage cans with a tight lid, frequent cleaning in the kitchen, and regular vacuuming. Any water leaks, such as dripping taps, should also be repaired. It is also helpful to seal off any entry points, such as holes around baseboards, in between kitchen cabinets, pipes, doors, and windows with some steel wool or copper mesh and some cement, putty or silicone caulk. Once a cockroach infestation occurs, chemical controls may help alleviate the problem. Bait stations, gels containing hydramethylnon or fipronil, as well as boric acid powder, are toxic to cockroaches. Baits with egg killers are also quite effective at reducing the cockroach population. Additionally, pest control products containing deltamethrin are very effective.
This Cockroach Page is Copyright The Animal Web Guide © 2004 - 2009 Chuck Ayoub