Cockroaches: Annoying Pests, Interesting Pets, and Living Robots
Cockroaches in North America are generally detested and even feared animals. I can certainly understand these feelings. They are interesting insects, though. Most of the world's cockroaches are not pests, and at least one type is kept as a pet. Even the pests can be useful. Their movement has inspired the creation of robots that can move quickly over a wide variety of terrain. Living cockroach "robots" are also being created.
Most of the approximately 4,000 species of cockroaches on Earth live in warm and moist tropical and subtropical forests. The species that invade our homes and other buildings can be a serious nuisance and cause health problems. This article focuses on the American and German cockroaches, which are found in North America and are often pests, and the Madagascan hissing cockroach, which is more benign and even liked.
Fossil evidence indicates that cockroaches have been on earth for over 300 million years. They are considered one of the most successful groups of animals.— Pennsylvania State University
The Body of a Cockroach
Cockroaches are generally between half an inch and two inches long. They have flat and oval bodies. North American roaches are a shade of brown or black, but some of the tropical ones are green or yellow in color.
As in other insects, the body of a cockroach has three sections: the head, thorax, and abdomen. Long and flexible antennae are attached to the head. The antennae are sensitive to touch and smell. The head also bears the compound eyes and the mouth parts.
The thorax bears two pairs of wings. The outer, leathery pair hides the inner, membranous wings. Some roaches can fly, but not all of them can. Cockroaches also have three pairs of legs attached to their thorax. The legs have spines and are capable of moving quickly. Roaches normally travel at a speed of about one to two feet a second. The bigger ones may move even faster.
Roaches don’t breathe through their mouths. Instead, they absorb air through holes called spiracles on the side of their bodies. The spiracles lead to tubes called trachea inside the insect's body, which transport oxygen to where it’s needed.
German and American Cockroaches
German and American cockroaches are not the only roaches found in North America, but they are both common insects and they both invade homes. Some of their features are compared below.
- German cockroaches (Blattella germanica) are about half an inch long. American ones are around one and a half to two inches long.
- The German cockroach is yellow-brown in color and has two dark stripes behind its head. The American one is red-brown in color.
- German cockroaches prefer a warmer habitat and are most often found indoors. In North America, a home invasion by roaches is more likely to be caused by the German cockroach than the American one.
- American cockroaches often live outdoors. When they do enter a home, they are frequently found in basements and drains. German cockroaches tend to invade areas of the home that are frequented by humans, such as kitchens and bathrooms. They favor warm and humid areas.
- German cockroaches may glide, but they don't fly. The American cockroach can fly, but it doesn't do this often.
Diet and Behaviour
Cockroaches eat a wide variety of materials. This factor has contributed to their pest status. They eat both human and pet food. They also eat garbage, plants, the glue in book bindings or on the back of postage stamps, soap, toothpaste, paper, and fabric.
Roaches are nocturnal creatures. During the day, they hide in dark places, such as cracks, drawers, and cupboards. They may be discovered in the spaces behind pictures and wall clocks, in heating ducts, and in areas around plumbing and sewage pipes. They are sometimes seen in drains, under sinks, and behind stoves and refrigerators. The insects may be found near a refrigerator’s motor. Some roaches infest garages.
Roaches quickly run for cover if the light is turned on when they're in an open space. They have two antennae-like extensions called cerci at the end of their abdomen. The cerci are very sensitive to air currents, including those created by someone trying to sneak up on the insects.
Roaches and Human Health
Some cockroaches—such as the American cockroach—may come into contact with human feces in sewers and with animal feces in a variety of locations. If they then walk over human food, they may contaminate it with bacteria. These bacteria may include the species of Salmonella and Shigella that cause food poisoning. In addition, roaches deposit their saliva and feces in our food. German cockroaches are also believed to transmit bacteria and viruses, including organisms that cause hepatitis, typhoid fever, dysentery, and gastrointestinal disorders.
As the insects move, they often leave a trail of feces behind them. The feces contains chemicals that transmit messages to other cockroaches. These messages include the route that a roach is taking to find food or water. The fecal trails may appear as dark stains or black specks. Cockroaches also release smelly secretions that can affect the flavor of foods and fill the air with an unpleasant odor when a large number of the insects are present.
Cockroach feces, saliva, and secretions can cause allergies and asthma in humans. The body coverings that roaches shed when they molt and their empty egg capsules can also trigger allergic responses.
Surprising Facts About Cockroaches
Researchers have discovered some surprising facts about cockroaches. Some of the discoveries have been made in a particular species, so it may not apply to all species of the insects.
- Cockroaches can survive for one to two weeks without drinking and up to a month without food.
- Some roaches have survived for forty minutes without air.
- A cockroach can survive without a head for up to a week. The brain is located in the head, but there are ganglia, or collections of nerve cell bodies, in other parts of the animal's body. These ganglia are responsible for a lot of a roach’s activities.
- A headless roach dies of thirst, since without its head it can’t drink.
- Each of a cockroach’s eyes is made of 2000 lenses, compared to the single lens in a human eye.
- It's often said that in a nuclear war only cockroaches would survive, since they are resistant to radiation. Experiments have shown that cockroaches are about six to fifteen times more resistant to radiation than humans. Some insects—such as fruit flies—are much more resistant than roaches, however.
Cockroaches of the opposite sex attract each other at mating time by releasing chemicals called pheromones. Usually the female produces pheromones to attract the male. In some species, the male produces pheromones.
After mating, most females produce an egg capsule, which is called an ootheca. The female carries the ootheca around under her body at the end of her abdomen. She usually drops it shortly before the eggs hatch. The egg capsule contains from twelve to sixty eggs.
The hatched young are called nymphs. They are white at first but turn brown within a few hours. They look like miniature adults except for their undeveloped wings. The young take one to four months to develop into full-sized adults. An adult female may produce up to eight egg capsules in her lifetime, which is up to a year for the German cockroach and one to two years for the American cockroach.
Madagascar Hissing Cockroaches
The Madagascar hissing cockroach, or Gromphadorhina portentosa, is often kept as a pet. It's a large and wingless cockroach with an oval body that reaches two to four inches in length. The roach is an attractive insect with a shiny appearance. It's brown in color and has dark red or tan patches.
The hissing cockroach is one of the many fascinating animals that live in Madagascar. In its natural habitat, the insect eats fruit and other plant parts on the forest floor and is not a pest. It's mainly nocturnal but may be seen in the day. The roaches live in colonies headed by a male, who actively defends his territory against the intrusion of other males.
Although the hissing cockroach can't fly, it has special pads on its feet that allow it to climb on a wide variety of surfaces. The pads are hooked. Anyone wanting to keep the cockroach as a pet should keep its ability to climb in mind.
Insect Horns and Hisses
The male hissing cockroach has a pair of protuberances behind his head. These are often referred to as horns. The animal uses his horns to ram into another male during a fight. The female has horns too, but they are much smaller than the male's.
The cockroach makes a hissing sound by exhaling air through a pair of special spiracles on its abdomen. The sound is made during courtship and during interactions between males. It's also used to scare predators.
Hissing Cockroach Reproduction
The reproduction process of the hissing cockroach is unusual compared to that in North American species. The animal is ovoviparous, which means that the eggs in the ootheca hatch within the female's body. The young are then born live.
The hissing cockroach gives birth to thirty to sixty babies at a time. These are white in color and like those of the insect's relatives are known as nymphs. The nymphs take five to seven months to mature, molting and darkening in color as they grow. The cockroach can live for two to five years.
Scientists are creating robots that move like cockroaches. Their goal is to create robotic devices that can run rapidly over varied terrain and change direction quickly, just like the real insects do. The robots could be sent into areas that are too difficult or too dangerous for humans to travel though. They could also send messages to humans if they have the right equipment. Scientists even envision cockroach-like robots that could communicate wirelessly with each other, forming a network.
European scientists have created a robot cockroach that mimics some aspects of a roach’s behavior and is accepted by the insects once it's covered by an appropriate pheromone. The scientists found that the insects follow the robot, even moving from the dark into the light, an abnormal behavior for most cockroaches. Scientists are using the robot to study the behavior of cockroaches when they are in groups. The device may one day be used to control roach populations.
Hybrid Robots From Living Insects
In a relatively recent development, scientists have begun the process of creating living cockroach robots. They've attached robotic devices to the backs of cockroaches. These devices connect to the nervous system of the roach. The goal is to control the insect's legs to force the roach to go where we want. The researchers are already having some success with this goal.
The research into creating "robo-roaches" is certainly interesting, but I also find it worrying. I don't expect that many people will complain about cruelty to roaches. The technology has also been used to create remote-controlled rats, however. Rats are intelligent and sentient creatures. The future development of the technology concerns me. It could certainly have benefits, but it could also be used inappropriately.
More Than Just a Pest
Scientists believe that cockroaches have lived on Earth for about 320 million years (and possibly for longer), with little change in their bodies. They are very successful creatures. The pest species can certainly be annoying and are understandably hated by some people. There is much more to cockroaches than the ability of a few species to act as pests, though. I think they are fascinating animals.
- American cockroach information from the University of Florida
- German cockroach facts from Pennsylvania State University
- Cockroach biology from Texas A&M AgriLife Extension
- Madagascar hissing cockroach facts from the University of Kentucky
- Creation of hybrid cockroach robots from The Royal Society Publishing
© 2010 Linda Crampton