A big black cockroach in the house is almost always an American cockroach or one of its close relatives, and it usually lives in the roof, wall cavities, subfloor or drains rather than in the room where you saw it. The Victorian Department of Health page on cockroach pest control says American cockroaches tend not to infest the living areas of a building. They live in roof, wall and subfloor spaces and around sewers and grease traps, then come out at night looking for food and water.
Which big cockroach is it?
The Victorian health page describes four larger species that get into houses:
- American cockroach. The largest common pest species at 35 to 40 millimetres. It is reddish brown with a pale yellow border around the plate behind the head, and it can fly short distances in warm conditions.
- Smokybrown cockroach. About 30 millimetres, shiny dark brown to black and fully winged. It flies in warm weather and is often drawn to lights at night.
- Australian cockroach. About 35 millimetres and dark brown, with yellow markings on the thorax and along the front edges of the wings.
- Oriental cockroach. Smaller at 20 to 25 millimetres, evenly dark brown to black, and it generally does not fly.
In poor light most of these look black, which is why the Better Health Channel simply calls American cockroaches large and black. None of them is the small brown German cockroach that breeds in kitchen cupboards.
Could it be a native bush cockroach?
Sometimes. Australia has about 450 cockroach species and only five are considered pests, according to the Australian Museum. Its page on native cockroaches says virtually all cockroaches found outside homes are native species, and none of the roughly 400 natives is a serious pest. The exception the Museum names is the smokybrown cockroach, an introduced species sometimes found in gardens and bush near houses.
That matters on the bush edge. Engadine is bounded by the Royal National Park on the east and Heathcote National Park on the west. A family there finding a large dark cockroach on the back deck every week may only be seeing a native passing through, but one that keeps turning up in the laundry at night is more likely a smokybrown living in the subfloor. That pattern is worth booking cockroach control in Engadine for, so a technician can name the species before anything is treated.
Where do big cockroaches come from?
From the spaces around the house that stay dark, damp and undisturbed. The Victorian health page lists where each species lives:
- American cockroaches live in roof, wall and subfloor areas and in and around sewers and grease traps. They prefer coastal areas.
- Smokybrown cockroaches dry out easily, so they stick to damp, dark, poorly ventilated places such as sheds, wall and roof voids, subfloors, mulched garden beds and drains.
- Australian cockroaches usually live outside around shrubs, woodpiles and leaf litter, and sometimes move into subfloor, wall and roof voids.
Drains are a common way in. A NSW Public Health Bulletin overview of cockroaches notes that several species live in sewers, escape through poorly fitting manholes, vent pipes and drains, and can pass through the water in the S bends of plumbing fixtures.
Gymea Bay is a bushy peninsula on the north side of the Port Hacking estuary. A Gymea Bay home where big cockroaches keep appearing beside the shower drain and the laundry tub, with leaf litter piled against the sandstone footings outside, needs cockroach control in Gymea Bay that looks at the drains, the subfloor and the garden edge together.
Why do you see them at night?
Because that is when they feed. The Victorian health page says cockroaches are generally nocturnal and that active cockroaches seen during the day often point to a large infestation. Smokybrowns are attracted to lights, so an open door or a lit window on a warm evening can bring one straight in.
An American cockroach female can produce up to 50 egg capsules in her lifetime, each holding 12 to 16 eggs, and the young take 6 to 12 months to reach adulthood. A colony in a roof void can build for a year before anyone notices.
Bonnet Bay's houses went up between 1969 and 1985 on sandstone gullies above the Woronora River. One big cockroach on the hallway ceiling each night in a Bonnet Bay house can mean a colony above the cornices, and that calls for fast cockroach control in Bonnet Bay that includes an inspection of the roof void.
Are big cockroaches a health risk?
They can be. Better Health says cockroaches are believed to spread illnesses such as salmonella and gastroenteritis because they feed on anything from food spills to rotting rubbish, and that studies have linked them to allergies. The NSW Public Health Bulletin describes cockroach allergens as strong triggers of asthma in children.
Why do surface sprays miss the source?
Because the cockroach you spray is a forager, not the colony. The Victorian health page says space sprays are unlikely to reach cockroach hiding places. The NSW Public Health Bulletin adds that control of American cockroaches also means treating underfloor, wall and ceiling spaces, drains and parts of the garden. Better Health says a heavy infestation needs a licensed pest control operator.
Sylvania is known for its large waterfront properties on the Georges River. A Sylvania house with a damp subfloor, a timber boatshed and thick mulched beds along the water side gives smokybrown and American cockroaches three places to live within a few metres of the back door. Spraying the kitchen floor will not touch any of them, so book cockroach control in Sylvania that covers the outbuildings and subfloor as well as the house.
Before you book
Note the size and colour of the cockroaches you see, and whether any have flown. Write down which rooms they turn up in, the time of night, and whether they appear near drains, ceiling vents or the laundry. Mention a damp subfloor, sheds, woodpiles or heavy mulch near the walls. Send those details when you contact our team for household pest control in the Sutherland Shire: call Sutherland Shire Pest Control Pro on 02 8360 3033 or email [email protected], so the technician knows where to look first.