How to Get Rid of Large Cockroaches

Last Updated: July 2, 2026

Gordon Reidy

Cockroach control, Cockroach treatment

Large cockroaches certainly have a big “eek” factor. Their large size, fast scurrying movements and ability to fly are all too much for some people. The good news is that if you have a problem with large cockroaches, they are relatively easy to control.

Adult American cockroach – up to 5 cm long

Typically large cockroaches live outside, although they can sometimes set up residence inside the home. More often they come inside “by accident” or when looking for water during dry periods. However, if there is a big population outside, the population overflow is likely to start causing problems inside.

There are 3 key steps to the cockroach control process:

Find the source of the infestation
Apply the correct cockroach treatment
Prevent the cockroach problem returning

Find the source of the infestation

Large cockroaches will often hide outside in drains and sewers, rubbish bins and garden beds. However, they will also congregate in sub-floor areas and basements where it is damp and cool. The somewhat strange hiding place is the roof void where they hide under the insulation – strange in that it is hot and dry!

Apply the correct cockroach treatment

Outside:

Using a long lasting residual spray (labelled for cockroaches), spray the following outside areas;

Perimeter of the home (1m up the wall and 1m out from the wall)
Around doors, windows and other openings
Known cockroach hiding places

PestXpert Pro-Spray Outdoor Perimeter is ideal for outdoor cockroach treatments.

Inside:

Use a residual spray which can be used around the perimeter of rooms / cupboards where there may be particular cockroach hotspots. If there are sensitive areas, which you may not be comfortable spraying (or the label does not allow use), the of cockroach baits such as PestXpert Cockroach Gel Bait is ideal.

Targeting cockroach hiding places such as under fridges & dishwashers, under sinks, inside cupboards and in other cracks and crevices. An aerosol with an extendable nozzle is ideal for targeting these hard to reach places (such as PestXpert Pro-Spray Crawling aerosol).

Bombs / Foggers:

If you have an infested room or a particular problem in the roof void / sub-floor consider using a cockroach bomb / fogger. You may need more than one for larger areas, but these deliver a great “fumigation” effect. Make sure you follow all safety directions.

PestXpert Pro-Fogger contains a unique triple action formulation and stability stand for professional results.

Prevent the cockroach problem returning

For large cockroaches, a regular treatment twice a year to the perimeter of the home and around likely hiding places, will do wonders. However, there are some key preventative measures which will also help:

Keep rubbish in sealed bins
Make sure insect screens on the windows and doors are in good shape
Seal any cracks / openings that may allow cockroach entry
Avoid storing goods (especially cardboard boxes) under the house
Keep garden beds away from the immediate perimeter of the house

For more information on cockroaches, prevention tips, control techniques and cockroach products, check out our other cockroach blog articles or visit our cockroach control page.

Types of large cockroaches in Australia

There are 4 mains species of large cockroaches in Australia that are considered as pests – the Australian, American, Smoky brown and oriental cockroaches. The first three species look quite similar (up to 40 mm long and dark brown) and are very good flyers. The oriental cockroach is very different in that it has shortened wings and cannot fly. They are all peridomestic cockroaches found in leaf litter, drains, sewers and sub-floors (and occasionally roof voids) and can be all controlled and prevented from becoming a problem with the actions tried above.

Australian cockroach

The Australian cockroach is identified by its pale marks on its pronotum (behind its head) and along the upper edge of the forewings. Found primarily along the east coast (in the warmer areas) and not common in Melbourne.

American cockroach

The American cockroach is very similar to the Australian cockroach, although it lacks the pale markings on the forewings. It is found across Australia but more common in the tropics and along the east coast.

Smoky brown cockroach

The smoky brown cockroach is a dark brown cockroach with no pale markings. It prefers tropical and sub-tropical areas.

Oriental cockroach

The oriental cockroach is dark brown cockroach, smaller than the other large cockroaches (around 25 mm long) and cannot fly as it does not have fully formed wings. It tends to be found the cooler, more temperate parts of Australia.

FAQ – Large cockroaches

How do large cockroaches get into the house?

As large cockroach primarily live outside and come inside by accident or looking for food, there are a number of entry points to consider. Windows and doors are obvious entry points, especially if there are non insect screens. Cockroaches that can access the sub-floor or roof void from outside can easily find their way into the main part of the house.

Should I be worried about one large cockroach in the house?

By itself one cockroach in the house doesn’t necessarily mean you have an infestation, but for many, even one cockroach is one too many! A single cockroach could get into your house through a number of routes, including through open doors and windows. However, as the saying goes, “for every cockroach you see, there are 20 back in the nest”, if you do spot a single cockroach it could mean you have an infestation. A thorough inspection and cockroach treatment will eliminate any cockroach problem if you have one and prevent one if you don’t.

If you do have an infestation it is likely to be outside, but if the conditions are right, large cockroach species can set up home inside buildings.

PestXpert Products for Large Cockroach Species Treatments

Originally Published: October 24, 2016

Author:

Gordon Reidy

Gordon Reidy has over 30 years experience in Pest Control Product Development and Product Safety. As the lead formulator at PestXpert, he has helped develop some of Australia’s most trusted household pest solutions. With a PhD in Toxicology, Gordon is passionate about delivering effective, science-backed products that are safe for families and the environment.

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