A cockroach scurrying across a kitchen floor will inevitably be a source of disgust and alarm to a home or business owner. This response is not new. These insects have appeared in poems, songs and books since antiquity. They have always been viewed as dirty, smelly and the carriers of disease.
Despite their reputation, the vast majority of cockroach species cause no problems nor pose any threat to humans. Of the over 4,500 known species worldwide, only about 30 are associated with human habitation and an even smaller number are actual pests. Of the 450 or so species of cockroach found in Australia, less than a dozen are likely to be encountered in a home or business environment.
Cockroaches are remarkably hardy. They live in a broad range of habitats, from the tropics to the Arctic. Some species can withstand temperatures as low as -122°C due to their ability to make a type of antifreeze out of glycerol. They can survive for weeks without food or subsist on the glue from a postage stamp if necessary. There has even been a report of a cockroach that stayed alive without air for 45 minutes.
Cockroaches smell. Some people are able to detect their odour long before they can see them. The insects also produce sound. Some hiss, while others chirp.
Due to their habits and hardiness, cockroaches can be troublesome pests to eradicate.
Cockroaches are social insects, using collective decision making when nesting and feeding. Pheromones are used to signal to other cockroaches to join them and these chemicals will determine how the growing number of roaches behave together.
The behaviour of individual roaches differs greatly from those in groups. Groups feed more readily and breed faster. As the group grows, the pheromones are believed to encourage more roaches to join if the food source is sufficient. This can lead to swarms.
Most native cockroach species will devour only leaf litter and rotting wood, but pest species will eat almost anything, including human food, rodent droppings, cardboard, pet food or even plastics. This ability to survive – or even thrive – on such a varied diet is one reason they can quickly become pests.
Pest cockroaches are often found in unsanitary conditions, among rubbish or even in sewers. Their habit of feeding on rotten food, putrefying animals or faeces means they are passive carriers of a range of bacteria. They can transmit those bacteria through contact with our food when they contaminate it by eating it or via their droppings, which can harbour bacteria. This risk is ever present and any cockroach infestation should be dealt with promptly.
Several serious diseases have been associated with cockroaches, including salmonella, staphylococcus, streptococcus and gastroenteritis. Although 32 bacteria have been found in cockroaches, most of these have been observed in laboratory tests rather than during actual disease outbreaks. The risk of them causing a severe outbreak of disease in a country like Australia is minimal.
Cockroaches have been implicated in several disease outbreaks, for example:
- a spate of Hepatitis A in Los Angeles,
- dysentery cases in Northern Ireland,
- an isolated typhoid occurrence in Italy
- Klebsiella pneumoniae outbreaks in the neonatal wards of hospitals in Ethiopia and South Africa.
There are many more cases but it is not always easy to prove that it was cockroaches alone which were responsible or whether a combination of other factors were involved. In the first three instances, the diseases could have been quickly brought under control if the vector, in this case the roaches, was identified sooner. Poor hygiene habits are often behind any roach-related disease problem.
Cockroaches are also known to carry the eggs of several species of helminths, better known as tapeworm, roundworm and their relatives. Roaches are also known to be carriers of a range of allergens, which can affect susceptible people. Long-term exposure to some of these allergens can exacerbate asthma in sufferers.
Problems caused by Cockroaches
Although the risk of disease transmission is real, the cockroach’s reputation itself can be damaging. Their presence in a restaurant or hotel, or any business, could prove costly in terms of lost business and damage to the business’s brand. Local authorities may even become involved and impose fines or restrict ongoing activities.
Residents in some South Melbourne flats had trouble of a different kind. In the 30 storey block, a few of the apartments were empty and left in a poor condition. A severe infestation of roaches made life miserable for those tenants who kept their dwelling clean. One complained that his dishwasher had been damaged beyond repair by the pests chewing through wiring. Several other electrical items had also been destroyed.
The cockroaches came and went through the communal heating vents. Local pest controllers were unable to bring them under control. Residents signed a petition to call on the local authorities to step in but legislation was vague about who was responsible, the landlord or the tenants? Fumigation was later ordered by the Minister for Housing.
Native Australian Cockroaches
Occasionally, a pest controller will be called on to identify and eradicate a non-pest species. Although the more than 450 species of native cockroach can be found in a wide range of environments, some will find their way into homes. If you have a basic knowledge of our native species, you may allay the home owner’s fears if they are confronted by one of these harmless intruders.
Most native Australian roach species are nocturnal. During the day they hide mainly under rocks, logs, rotting wood and among leaf litter. Most are forest or grassland dwellers, a few inhabit caves, and a small number live in ant nests. Their food requirements and habits differ from pest species, so the risk of spreading bacteria and disease is negligible.
Australia is home to some fascinating native cockroach species. The most famous is the Australian Giant Rhinoceros cockroach, Macropanesthia rhinoceros. This is the world's heaviest cockroach and can weigh more than 30 grams, growing to over 9cm in length. Overseas it is highly prized in the exotic pet trade and live specimens can sell for a high price!
Like their close relatives the termites, cockroaches undergo incomplete metamorphosis. From the egg a nymph will hatch that resembles a small version of the adults. It will probably be lighter in colour.
Wings are present on both sexes of many adult cockroach species but not all. Depending on the species, it may be just the males that have the wings whereas in another only females have them. In yet other types, neither sex has wings. If wings are present, they will only appear at the last moult.
In most species, the female cockroach produces a hardened egg case called an ootheca. The word ‘ootheca’ comes from two Greek words that mean ‘covered egg’. This can contain from ten to several dozen eggs depending on the species. The majority of species lay their oothecae hidden in a corner or under cover and leave them to hatch on their own. In a few species, the ootheca is partly laid but then pulled back inside the female to continue its development until the live young emerge. Some observers confuse this with live birth but it is not. However, one species does not produce an ootheca at all. Her young develop inside her much as a mammal would, appearing as live nymphs.
The number of eggs laid, the time they take to hatch and for the nymphs to become adults depends on the species. Other factors also play an important role, such as temperature and the availability of food. For some species, the lifecycle can be a little as a few weeks but for others it may take as long as a year.
German cockroach (Blattella germanica)
This is one of the smaller pest species, with adults normally between 10 and 16mm long. It is a common pest, found throughout the world. A German cockroach is easily identifiable, as the adult has two parallel narrow bands of black running along the top of its tan-coloured thorax. The nymphs also have the same markings but as they are darker in colour these are not so obvious.
Although both sexes have wings, they rarely fly and prefer to scurry out of sight. When large numbers are present, it is often possible to smell the cockroaches as they secrete several odorous compounds.
German cockroaches are able to survive on almost anything. They have been known to eat soap, books and even toothpaste. This cockroach likes warm, humid conditions. It favours kitchens and bathrooms in homes, and similar environments in commercial properties.
Signs to look out for are the pepper-like droppings and discarded ootheca. The female keeps the ootheca attached to her body until a few days before they are due to hatch, so you will probably only find empty egg cases.
This is the largest of the pest species, with adults up to 4cm long. They are reddish brown, and the nymphs resemble the adults, except they lack wings. The wings of the male are slightly longer than those of the female.
Despite its common name, the species probably originated in Africa. Also known as the Ship cockroach or the Bombay Runner, American cockroaches have spread around the world, occasionally reaching plague proportions in warmer countries.
These roaches are good fliers and can extend their range by flying from one location to another. They are also fast runners, quickly able to disappear from sight when disturbed. They have been clocked at 5.4km/h, which makes them one of the fastest running insects.
American cockroaches prefer moist areas, and temperatures around 29°C. If the weather turns colder, then they will search for somewhere warm, which invariably means human habitation. They are common in basements, sewers, drains – anywhere that is warm and damp. They can also survive in drier conditions if they have access to water.
An American cockroach female may produce about 10 oothecae during her life, each containing around 10 to 15 eggs. These are dropped out of sight, in a safe location. The oothecae are just under 10mm in length and brown. Nymphs normally hatch after about six to eight weeks, maturing over the next six to twelve months depending on the availability food and the temperature. An American cockroach can live for an additional year after maturing.
Like most of the pest species, American cockroaches are omnivorous. They can survive on a variety of food, such as leather, books, paper, glue, and hair. They are also cannibalistic if they come across dead or wounded roaches.
This is a small species of cockroach, measuring from 10 to 14mm in length. Its colouring is distinctive. Nymphs are tan or light brown, often darker at the head end. They have two transverse lighter coloured bands across the body. In adults the rear band may be obscured by the wings but the front band is always obvious.
The female has a broader body but shorter wings than the male and cannot fly. The male is a good flyer.
This species needs less moisture than the German cockroach and prefers higher temperatures. They are less likely to inhabit bathrooms and kitchens but may be found in furniture or near electrical appliances for the warmth. With less dependency on moisture, they can spread further into a building than many other species, often seen on walls or near the ceiling.
Although they are nocturnal, they may be seen scurrying in search of food in the daytime or if they are disturbed as a cupboard or drawer is opened. Like most pest species they are omnivorous but with a preference for starchy products, such as wallpaper paste and book bindings.
A female Brown-banded cockroach can lay up to 15 oothecae during her life, each of which might contain 10 to 18 eggs. The nymph takes approximately 90 days in ideal conditions to reach maturity, after which the adult may live a further six to ten months. The oothecae are small, barely 5mm in length and normally attached to the underside of something or in a crack.
Oriental cockroach (Blatta orientalis)
An adult of this species will grow to between 20 and 30mm long. Although both sexes have wings, a female’s are very short. The male’s wings only extend part way down its abdomen and the male will rarely fly, only remaining airborne for short distances.
The female is slightly longer than the male and has a wider body. Both sexes are shiny and normally black, although a few are dark brown.
Although Oriental cockroaches prefer warmth, they can tolerate colder conditions than the other pest species. Their partiality for damp places is responsible for another name: ‘waterbug’. They are usually found at ground level and may live in drains, basements or under wooden flooring. In the summer, colonies may exist in the garden among leaf litter or beneath bushes but as the weather cools they will move into nearby homes for warmth.
The Oriental cockroach’s habit of living in dark, damp spaces out of sight can make them hard to detect. They like decayed organic food, such as compost heaps and are often found near garbage bins.
A female can lay about 8 oothecae, containing 16 eggs in each. The oothecae are dropped in a safe location and hatch in about 60 days.
Where the winters are cool, the Oriental cockroach will only produce one generation a year but in warmer climates they will breed throughout the year. Nymphs will normally take between six and twelve months to reach maturity depending on the climate.
Although this reddish-brown cockroach is similar in appearance to the American cockroach, it is easily distinguished by the yellow markings on its thorax and the yellow lines along the wing edges. It is also smaller, adults normally only growing to between 25 and 35mm in length. Despite its name, the Australian cockroach probably originated in Africa.
The Australian cockroach lives primarily outdoors but will invade a home if the weather turns cold or food is freely available indoors. They feed mainly on plant matter but will eat human garbage if necessary. Outdoors they live in tree holes, leaf piles and wood stacks. Adult roaches are excellent flyers.
An adult female may produce up to 30 oothecae during her lifetime, which she drops in cracks or hides in other safe places. Each ootheca can contain about 25 eggs. The time taken from egg to maturity is about one year.
Smoky Brown cockroach
At first glance, the Smoky brown cockroach could be mistaken for a small American cockroach. However, they are slightly darker in colour and the adults’ wings are longer.
Like the Australian cockroach, this is primarily an outdoor species. It might venture indoors at night, attracted by light, food or moisture. It needs to drink more than most species. Its food mainly consists of plant material but like all the cockroach scavengers, it will eat whatever is left lying around.
This species lives for about a year. The female lays around 15 ootheca during her life, each of which may contain up to 25 eggs.
Due to their secretive nature, searching for cockroaches, or even signs of their presence, can be difficult. You may have to rely on the home or business owners to tell you where they have been seen in order to begin your search in the right place. It helps if you know which species you are looking for, as their habits vary. During daytime, most will retreat to dark, damp and warm places, especially near their food source.
Patience is required for a cockroach inspection. You may even smell the cockroaches before you spot them if the density is high enough for the smell to be noticeable. Different species have their own odour. It may be necessary to get down on the floor, even crawling around, to detect signs of the roaches’ presence. From a standing position you are likely to miss clues.
Cockroach droppings of the smaller species are often likened to pepper – little black dots less than 1mm wide. Larger species will have correspondingly larger droppings, being longer but of similar width. These will accumulate near food sources and along cockroach runs. They are easy to overlook.
Cockroach runs are a tell-tale sign of the pest’s existence in the home or business premises. You may notice smear marks on horizontal surfaces or along the junction of a wall with the floor. The brown marks will be more noticeable if the cockroaches have access to abundant water.
You may also find dead roaches, especially in bathrooms, outhouses or garages. Other signs would include damage to food packaging and paper, such as piles of old newspapers.
Not all species are found at floor level and the search should also include areas near the ceiling, on the tops of wardrobes, tall cupboards or shelving. A mirror on a stick like the ones used by car mechanics are useful for this purpose. It will also help you to see under tables or behind fridges and washing machines.
Sometimes it will be necessary to look under objects that are too heavy to lift and your mirror won’t reach. You will need to go down on your hands and knees – so consider investing in knee pads and have a torch with you.
If you are checking somewhere with no natural light, a basement for example, turn off the lights and wait. After a few minutes you may hear scurrying. Even if you don’t, turn on the lights. You might see roaches darting for cover. Watch where they run as they could lead you to larger numbers.
Occasionally you may need to visit a premises at night in your quest to locate cockroaches. Obviously a good torch is essential. Avoid overly bright torches as they can be hard on the eyes if used for an extended period. Using a head-mounted torch in conjunction with a hand-held one works well. You can buy colour filters that allow you to see well but which prevent the light being detected by the insects so they will carry on their normal behaviour in your presence.
Sticky traps can be used to identify the species involved or if you are struggling to spot any specimens. Once you have caught one or two individuals, you will know what you are dealing with and can decide on the appropriate action.
The key to stopping a cockroach problem is to implement a twofold program. The first part involves preventative measures that require the help of the home or business owner. No matter how many cockroaches you kill, the pests will keep returning if what attracts them is still present. The second part is the eradication of the pests using chemicals.
You can provide the home or business owner with the following list of preventative measures so that they can take action themselves. If they are unwilling to take responsibility for these simple tasks, it will not be long before the roaches return.
To avoid embarrassment or confrontation, it may be wise to assure the owner that this is a list of routine precautions given to each customer and does not imply they keep their premises in an unsanitary condition.
- Remove any food source that might attract roaches. All food items should be appropriately stored, either in the fridge or in sealed plastic containers or bags. Pet food should not be left out overnight.
- All spill, crumbs and waste food should be cleaned up daily, especially on work surfaces where food is prepared.
- Indoor rubbish bins should be emptied daily.
- Outdoor garbage bins should have tight-fitting lids. It is common for waste food to be spilled around the garbage bin area. This should be cleaned up.
- Where possible, all cardboard boxes, old magazines and newspapers should be discarded as they are ideal hiding spots for roaches and may harbour oothecae.
- Entry points that can be used by cockroaches should be sealed. These may be around pipes or drains coming from outside. Drain vents and open pipes should be covered with fine wire mesh.
- Ideally, all joints between skirting boards and floors, and behind electrical sockets should be sealed.
- A kitchen stove can harbour food under the hob or behind the grill; both are perfect for roaches. Keeping these clean will deprive roaches of food.
- Repair any water leak to avoid the damp conditions welcomed by some cockroach species.
Baits and traps
Bait stations are plastic containers that contain a bait to attract cockroaches. They differ from traps in that when the cockroach is attracted to the bait, it eats but then leaves and dies elsewhere. Traps are open-ended boxes, normally made of plastic or cardboard, lined with a sticky substance. Bait is still used but is either built into the trap or added when being set. The roach gets stuck to the adhesive and dies.
Whichever is used, to be effective it should be placed in a location where the roaches feed and where the infestation is at its most severe. If other sources of food are available, such as pet food or dirty dishes, then the bait will likely be ignored. If the extent of the infestation is unknown, then traps may be placed in all the corners of the room. Other suitable places are behind fridges, under sinks and near cookers or ovens.
If successfully positioned, the first roach should be found stuck on the adhesive within 24 hours. If, after a few days, nothing is caught the traps should be relocated.
Many of the pesticides used in bait stations are slow acting. It might take seven days or more to see results in the form of dead roaches. Some baits use pesticides such as Oxadiazine, which blocks the insect’s nervous system. Others use one of the Insect Growth Regulators, IGRs, which interfere with the insect’s ability to moult.
The popularity of bait stations over traps is that they can be refilled and remain effective for several months. Traps need to be monitored and replaced regularly but are useful for catching and identifying pests.
In addition to bait stations, gel baits are available which can be put into cracks and crevices where the roaches will find it. The gels tend to dry out quickly and become ineffective after a few days, so will need to be reapplied.
Some cockroaches are no longer attracted to the normal baits used in traps. There have been reports of German cockroaches that avoid the glucose often used as bait. Other enticements may need to be substituted, such as peanut butter or tuna. Female roaches carrying ootheca feed less than their male counterparts and may not be caught as readily by baits or traps.
Aerosol sprays can be useful to quickly reduce the numbers of a large infestation. The sprays themselves not only kill but are also repellent to cockroaches, so they should not be used near baits or traps. The repellence may encourage the roaches to move to a different part of the premises.
Surface sprays are useful as a preventive measure. They should not be used near food nor pets. They are best applied to cracks and the inside of garbage bins.
The most common dust used is boric acid powder. It is a contact poison that is not repellent to cockroaches. If kept dry, it is effective for a long time. The powder adheres to the cockroach’s body due to the electrostatic charge and is ingested when the roach grooms itself. Boric acid powder can take up to a week to have a noticeable effect on the cockroach population.
The powder can be dusted into cracks and crevices or lightly spread in areas where people and pets are unlikely to come into contact with it. Particular caution should be taken where children are present. A thin layer is more effective than a thick one.
Diatomaceous earth and Pyrethrins are also often used in powder form, with the advantage that they are considered safer where children and pets are a concern. They act in a similar way to boric acid powder by desiccating the insect. Other cockroaches will be affected as they mingle and swarm near food.
As with all chemicals, caution is needed.