Wikijunior:Bugs/Cockroach

What does it look like?

An American Cockroach

A cockroach is similar to other insects in the way its body is constructed. The body is divided into three parts—head, thorax, and abdomen. Three pairs of legs are attached to the thorax. Most cockroaches have three joints on each leg, which means they have 18 knees!

The skeleton is made of a hard substance called chitin. When a skeleton is on the outside, it is called an exoskeleton. The exoskeleton supports and protects the roach’s insides. Because it is hard, the exoskeleton cannot grow. To get around this problem, a cockroach sheds its exoskeleton several times per year. Then its body grows quickly before the new exoskeleton forms. When the exoskeleton has just been shed, the cockroach’s skin appears very light. Then, after about eight hours, the skin becomes dark again.

Wings, when present, overlap one another and lay flat over the back, but the tips of the hind pair do not fold. There is a yellowish stripe along the front margin of each fore wing. Males usually have two sets of wings. Females either lack wings or have wings that are too small for flying. There are important sensory organs called cerci on the rear-most segment of the body.

At first, many cockroach species appear similar to each other, but have distinguishing characteristics when examined more closely. The American cockroach is often referred to as a water bug. It is 1-1/2 inches to 2 inches long. Its flat oval body is reddish brown. It has wings that are fully developed. There are yellowish edges and markings on the exoskeleton. The exoskeleton, known as the pronotum is usually bare or only slightly covered with silky hair.

The Oriental cockroach has an unusual scallop shape which comes from the way the rear, side corners of its abdomen point outward like edges of a scallop shell. It can be confused with American and Turkistan cockroaches because of its general appearance. However, a closer look will reveal distinguishing cream-colored markings behind the head and around the wings.

The male Oriental cockroach is about 1 inch long and has short, rounded wings. The female is larger than the male and can grow to 1-3/8 inches long. The female has very small wing stubs, so it is flightless. The Oriental cockroach is black or very dark, reddish brown. It is often called Black roach, Black beetle, or water bug because of its dark color and hard body. Another name is Asiatic cockroach. It is also called Shad roach because its young appear in great numbers just when shad are swimming into fresh waters to breed.

The German cockroach looks shiny and is generally brown or light brown in color. It has long slender legs, long, thin antennae, and wings. The Field cockroach is a species that is often confused with the German cockroach. It is olive in color with a black stripe between the eyes. The Madagascar hisser is one of the largest species of cockroach, reaching two to three inches in length when mature. Unlike most cockroach species, it is wingless.

Where does it live?

Most cockroaches live in warm, moist, tropical regions of the world, such as Florida and Mexico. Only a few species live close to people where they can find food easily. They often hide in dark corners of kitchens or near the stove where food gets spilled.

The majority of cockroach species have lived in the same places for a very long time, far away from people. An example is the Common wood cockroach, the country cousin of the city-dwelling pest cockroaches. It lives in the damp forests of South Africa, in areas where it can hide under logs and stones. It likes moist conditions. Another example is the Giant Cave cockroach from the rain forests of Central America and the Caribbean. It likes to live in caves with bats. Its young burrow into the bat droppings. The species lives outside caves too, where it shelters in hollow logs and trees.

Cockroaches are very successful creatures because they have not adapted exclusively to one habitat or food. They can survive in a variety of places. Entomologists, people who study insects, believe there are about 3,500 different species of cockroaches worldwide. About 55 cockroach species are found in the United States. In cooler areas cockroaches can be found all the way from Antarctica to Greenland. They find crevasses and corners inside warm buildings such as hospitals, ground-floor storage areas, homes, and basements. They rarely live outdoors in the cooler climates except during very hot, humid summer weather. California is home to six species of “pest” cockroaches. The German cockroach prefers kitchens, bathrooms, and areas where food is prepared or stored. Brownbanded cockroaches prefer warm areas indoors, behind pictures on walls, in hollow legs of furniture, and cluttered rooms. Smokybrown cockroaches like planter boxes, trees, shrubs, and vegetation.

A seventh species, the Field cockroach, is not really a pest since it is usually found outdoors in piles of leaf litter and plant debris. It is known to come indoors when it is hot or dry.

A bush cockroach

The German cockroach was introduced from Europe and has become widely established in cities.

The American cockroach was introduced to the United States from Africa as early as 1625. It has spread throughout the world by commerce. It prefers sewers, water meter boxes, and storm drains. It is at home in steam tunnels of large buildings like hospitals and places where animals are raised.

The Oriental cockroach usually lives outdoors and likes cool damp, dark places such as woodpiles, ivy, ground cover, garages, basements, water meter boxes, and drains.

Turkistan cockroaches usually live outdoors or in masonry areas away from building. They prefer water meter boxes, cracks between concrete blocks, piles of leaves, and potted plants.

In northeastern areas of the United States the American cockroach is a common pest. It often infests landfills and survives the winter weather by taking advantage of the warmth generated by piles of trash.

The unusual Hissing roach is originally from the island of Madagascar off the coast of Africa. It likes to live in rotting logs. It can be found in many parts of the world because people enjoy keeping it as a pet because of its appearance, large size, and interesting behavior.

What does it eat?

We think of dead animals, dung, and dead plant matter as waste to be disposed of. But to a Cockroach and tens of thousands of other insects, these are valuable food resources. A Cockroach is called an omnivore because it eats both plant and animal matter.

Some species, such as the Wood Cockroach, eat organic matter such as cellulose, a material that is found in trees and plants. The Wood Cockroach is usually found in the woods living under dead logs and stones. It can survive and grow on a diet rich in cellulose. It has overcome the difficulty of digesting cellulose by means of a specialized digestive system.

When a cockroach moves its feelers, it is sniffing the air. It uses its feelers as a nose. It can also smell with its mouth, which is handy for sniffing out food.

In general, cockroaches have powerful jaws to chomp through food. When chewing, the mouth moves side-to-side rather than up and down. The mouth parts point backward. The sense of smell is partly located in the mouth and partly in the feelers. Salivary glands in the mouth produce fluid to help digest food. The fluid from the salivary glands also allows it to spit—a nasty roach habit.

How does it defend itself?

Many cockroach species use defensive secretions that are extremely sticky and sometimes toxic. The upper side of the hindmost segment of the abdomen is covered with a sticky secretion. Small predators, such as centipedes and ants, are disabled when their mouth-parts or legs become entangled in the sticky secretion.

Madagascan hissing cockroach.

Inside the outer skeleton, a cockroach has a white substance called fat body. It is similar to the fat we have in our bodies. It stores energy. But, it also helps with digestion in a way that makes poisons, such as insecticides, less harmful.

A cockroach is very sensitive to movement, so it is hard to sneak up on one from behind. One way it senses movement is through two tiny hairs at the tip of the abdomen. These are called cerci. Even a tiny breeze caused by something nearby tells it something is happening. If it is frightened by the movement, it will zoom off in the opposite direction to whatever the cerci have detected.

A cockroach has a pair of compound eyes made up of tiny light sensitive parts called ommatidia. Each one of these acts like a single eye with a six-sided lens. Light passes through the ommatidia, then a nerve takes the image to the brain. The compound eye is very sensitive and can pick up light from different sections of the roach’s surroundings. The brain combines all the individual images from the ommatidia to create one complete image, or picture. Compound eyes are very useful for detecting small movements. As something moves, its image is picked up by a changing cluster of ommatidia. This immediately alerts the cockroach that an enemy is approaching.

The Madagascar cockroach is nicknamed “hisser” because of its ability to force air through small openings the abdomen. It is believed to be the only insect that can hiss in this exact manner. Hissing takes two forms: the disturbance hiss and the fighting hiss. Only the male uses the fighting hiss. The hissing sound is used to frighten away predators and to defend territory. Hissing is also a way to communicate danger to others.

What stages of metamorphosis does it go through?

A cockroach undergoes incomplete metamorphosis. It goes through three stages in the life cycle—egg, nymph, and adult. Just like young of other insect species, a cockroach develops inside a fertilized egg. The eggs are usually glued together by the female to form a packet, or egg case. It contains 16 to 64 eggs depending on the species and on how much food the mother can find. In some cockroach families the female keeps the eggs inside her body and gives birth to live young. The Cape Mountain cockroach does this. In some species the female carries the egg case inside until hatching time is close. Other species deposit their egg cases quite soon after they are formed.

The young cockroaches that are born alive stay with their mother for a day or so. Most are not born alive. Their mothers lay eggs that they hatch out of. As soon as they hatch they are on their own for survival. At first the newly hatched babies are soft and white. Soon after being exposed to air they harden and turn a darker color.

Giant Brazilian cockroach.

The creature that hatches from the egg is the nymph. It looks like the adult but is smaller and does not have reproductive organs or wings. Each time a nymph needs to grow, it has to shed its skin. This happens between five and fourteen times before adulthood is achieved. As the nymph grows, it gradually develops all of its adult features. The German cockroach nymph sheds its skin about six times in the 95 days it takes to become an adult. Depending on species and conditions, adults can live for as little as a month or for several years.

What special behavior does it exhibit?

A cockroach is a nocturnal creature, moving about at night time. It does not like the light. It tends to congregate with others in corners and generally travels along the edges of walls. It hides in dark, warm areas, especially narrow spaces where surfaces touch it on both sides. An adult German cockroach can hide in a crack 1/16 inch wide! The Madagascar hissing cockroach is an excellent climber and can easily scale smooth glass.

When disturbed, a cockroach will run rapidly. Its speed helps it quickly get away from danger and into a safe hiding place. Certain large tropical cockroaches hold the record for the fastest moving land insects in the world. Many species are wingless and depend on fast running speed to escape enemies.

A cockroach can do without food for up to a month. It cannot live without water for more than a week. Most of the water it needs comes from food.

How does this bug affect people?

Not all cockroach species are pests. Many live far away from people. As a decomposer they help recycle dead wood. They speed up the breakdown of dead organic matter.

Cockroaches become pests when they infest homes. They eat all kinds of food and sometimes destroy books, rugs, and clothing. Their presence does not necessarily indicate uncleanliness, but people are repulsed when they find cockroaches where they live.

Disease-causing organisms can be carried on the legs and bodies. Cockroach excrement and castoff skins contain allergens which cause skin rashes, watery eyes, congestion, asthma, and sneezing. Secreted odors can affect the flavor of various foods. When there are many cockroaches present, these secretions may result in a characteristic, unpleasant odor.

Cockroaches are able to live in cold conditions but will die if temperatures go much below freezing. When it gets too cold they move in with humans. They are attracted to large buildings with central heat and boiler rooms. The heating of buildings in winter has allowed roaches to spread to all the places where humans live. On the other hand, they cannot survive at very high temperatures, so heat is sometimes used to kill them. People have their homes wrapped in a very large canvas tent, and then blow heated air (140 degrees F) into it for four hours to get rid of the unwelcome guests.

References

Borror, D.J. & White, A.E. (Eds.). (1970). Roger Tory Peterson field guides,insects of America North of Mexico. Norwalk, CT: The Easton Press.

Jacobs, S., Sr. (2007). Entomological notes. [1]

Kirkwood, J. (1999). Cockroaches. In Nature’s children (Set 6). Danbury, CT: Grolier Educational.

Zim, H. & Cottam, C. (1987). Insects, A guide to familiar American insects. NY: Golden Press.