Pest cockroaches can be broadly split into two groups; the peridomestic cockroaches (the larger species) that live outside and around buildings; and the domestic species, such as the German cockroach which only live inside buildings.
The peridomestic variety typically live in the garden beds around buildings, in drains and sewers, and around garbage bins. They will also live in the sub-floor and roof voids of buildings. They will typically come inside when looking for food and moisture, or “by accident”, although they will sometimes establish populations inside buildings.
The domestic species, the German and brown banded cockroach, are the more challenging pests to control. Infestations can quickly develop due to their small size and ability to hide large numbers in small cracks and crevices, coupled with their rapid breeding cycle. German cockroaches have the nickname, the “five star cockroach”, for their association with restaurants and hotels!
With their ability to transfer disease (especially gastro illnesses), and their scurrying behaviour, they are viewed as a truly disgusting pest. Their presence in kitchens and food establishments is not tolerated by homeowners, business owners, their customers and health departments alike!
During their life-cycle, cockroaches undergo an incomplete metamorphosis – the young nymphs that hatch from the eggs have a very similar body format to the adults. This is very different from the complete metamorphosis of the butterfly where the caterpillar undergoes a complete change in body form in the pupae before emerging as a butterfly.
The duration of their life-cycle varies by species, with the smaller species such as the brown banded cockroach having a life-cycle as short as a few months and the larger species, such as the American cockroach, having a life-cycle as long as 2 years. Similarly the life-span of the adults also varies with the adults of the small species living up to 6 months and adults of the large species living up to 2 years.
As with all insects, the speed of the life-cycle will speed up in warmer weather.
Cockroaches don’t lay eggs, they lay egg cases (ootheca) which can contain up to 50 or more eggs depending on the species. The young will hatch out of their eggs inside the ootheca, emerging when the egg case splits open.
Some species ‘drop’ their egg cases in a safe location several days before they open, others carry the egg case until just before the young are ready to hatch.
Baby cockroaches are more accurately called nymphs. When they hatch from their eggs they are many times smaller than the adults, but will look very similar, except for the absence of wings. Young nymphs are not often seen, except in severe infestations, as they tend to hide in their harborages (nests).
Every now and then we will get a comment or question about the ‘white’ cockroaches someone has seen. These aren’t actually white cockroaches but are individuals which have just shed their skin.
Cockroaches have a hard cuticle (skin) which means to grow they need to shed their skins periodically. When they shed their old skin, for a short time the new cuticle is soft and white. It is during this short period that they can grow before the cuticle hardens and becomes the typical brown colour once more. They will go through several moults / instar stages before turning into an adult.
Only the adults can have wings. But in some species only the male has wings and in others neither the male or female have functional wings. Most of the large species (except the oriental cockroach) will fly, but generally this is only as a predator avoidance mechanism and generally only in warmer temperatures. Still, a cockroach flying into your face or your bedroom and be a pretty freaky experience!
Cockroaches don’t have nests, but more correctly have harborages where they congregate. Whereas the adults of most species don’t ‘look after’ the young, there are advantages in living in these communities. The nymphs typically do not stray far from the harborage, and will typically feed on the faeces and vomit of adult cockroaches! Scientists are still learning about these aggregations and various pheromones are thought to play a role in some of their communal behaviours.
The small species can set up these harborages in the tiniest of cracks and crevices. For example Germans will set up their home in door hinges, dishwasher control panels, kettles, microwaves, plug sockets and more.
Cockroaches are seen as “dirty” insects and with good reason. They have been shown to carry and transmit a large number of diseases including Salmonella and E. coli as they walk over food preparation surfaces, cutlery and crockery, and feed on human food.
Their droppings and their spent skins carry proteins that can cause significant allergic reactions and asthma. In the US, cockroach allergens have been detected in 85% of inner city homes, with between 60-80% of inner city children being sensitive to these allergens, which are a major cause of asthma attacks.
To eliminate a cockroach problem it’s important to identify the species and the location of the infestation. Typically problems with large species originate from outside and problems with small species are exclusively inside.
For large species spraying hiding places and the perimeter of the building (to stop them coming in) is often the best approach. But for small species such as the German cockroach, a thorough inspection is required and the use of specialised products.
For many it is easy and quicker to call an experienced pest professional as they can also access products which aren’t available in the supermarket or hardware stores.
The type of treatment a professional pest manager will provide will depend on the species present.
For large species a treatment will typically include spraying the outside of buildings, targeting the building perimeter, entry points, drains and garbage bins as well as treating any sub-floors or roof voids. The pest manager will typically use sprays outside and blow powder/dust into the sub-floor and roof void. In specific situations they may also use baits. For large species treatments, pest managers will commonly provide a 6 months warranty / service free period.
For German cockroach infestations the treatments are more specific and more of a challenge. Inspections are more critical to try and determine the scale of the infestation and potential hotspots. Baits and special cockroach sprays will be used to get on top of the problem. It can take a week or two to eliminate a German cockroach infestation and sometimes longer with multiple visits for a major infestation. Whilst pest managers will guarantee elimination of the problem, they will often not provide a warranty against re-infestation or if they do, it tends to be of short duration. This is because any treatment cannot protect against re-infestation, for example from egg cases brought in, in cardboard boxes.
Whilst homeowners can normally deal with the occasional invader with a quick spray from an aerosol, to get on top of an infestation (especially for German cockroaches), utilising a pest manager with their knowledge and access to high performing cockroach baits and specialised spray products, is generally the best option for complete and long lasting control.
For cockroach control in apartments / units, it is often better to treat the whole building, so speak to your body corporate.
When cockroach baits were invented they revolutionised cockroach control. They provided solutions to two main problems;
Cockroach baits consist of an attractive food matrix attractive and a slow acting insecticide. Foraging cockroaches will find and consume the bait. They are doomed, but because it is slow acting they tend to become ill several hours later, back in their harborage. With their droppings and vomit laced with the insecticide, the young that don’t leave the harborage will feed on these excretions, also picking up the insecticide and die. It is through this transfer of insecticide that complete population control can be achieved.
The skill in a cockroach treatment is to know where to place the bait, as German cockroaches rarely travel more than 2 metres from their harborage to feed. The highly attractive professional gel baits are ideally suited for the job (rather than the solid baits in plastic containers sold in supermarkets).
It will generally take 1-2 weeks to completely eliminate a cockroach problem, but for severe infestations it may take longer with additional visits.
The use of cockroach bombs (also called cockroach foggers or total release aerosols) are a popular DIY treatment. Much like flea bombs, the idea is that you can set one of in an infested room and when you return a couple of hours later all the cockroaches are dead, and the problem is solved.
Researchers in the USA, carrying our trials in infested apartments have shown that cockroach bombs don’t work. They also recorded that elevated levels of insecticide were found on kitchen surfaces.
Outside the house / building:
Inside the house / building:
BEWARE OF CARDBOARD BOXES! Keep an eye out for egg cases and cockroach nymphs coming in on cardboard boxes – this is a common source of infestation, especially for German cockroaches.
Our pest control library has more articles on pest control cockroaches, cockroach baits and cockroach research.
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