The five sheets · Sheet 02 · The roof and wall voids
Cockroaches: which one, and where in the house
The species matters, because each pest cockroach keeps to a different part of a building, and Victoria’s health department says identifying it helps decide how to inspect and control it. Most German cockroach infestations are in kitchens; the American, smokybrown and oriental keep mostly to voids, subfloors and drains; the Australian lives mainly outdoors; and the brownbanded scatters through a building, often up high.
- Sheet
- 02 of 05
- Applies to
- Descriptions, not rules
- Drawn from
- Victorian Department of Health, Better Health Channel, a 2024 PNAS study
- Checked
- 8 October 2026
General information, not health advice. The descriptions come from Victoria’s Department of Health and describe the insects, not a Victorian rule. For a heavy infestation, the Better Health Channel says professional treatment by a licensed pest control operator will be needed; in NSW, the EPA issues those licences.
Six species side by side
There are more than 4,000 cockroach species worldwide, and only a few are major pests, Victoria’s health department says. It describes six. Size and colour separate most of them; where you found it separates the rest.
| Species | Size and colour | Where it tends to live | Life cycle |
|---|---|---|---|
| German Blatella germanica | 12–15 mm grown; amber, with two dark stripes running lengthwise | Warm, humid, undisturbed spots; most infestations are in kitchens | Usually three to four generations a year, up to 40 young in each |
| American Periplaneta americana | The largest common pest species, 35–40 mm; reddish-brown, a pale yellow edge around the front of the thorax | Roof, wall and subfloor spaces, sewers and grease traps, more than living areas | Up to 50 egg capsules in a lifetime, 12 to 16 eggs each; 6–12 months to grow, and adults live 6–12 months |
| Australian Periplaneta australasiae | About 35 mm; darkish brown, yellow markings on the thorax and on the front edges of the forewings | Usually outdoors: shrubs, trees, woodpiles, bark and leaf litter; sometimes subfloor, wall and roof voids | Up to 20 egg cases of up to 24 eggs; 6–12 months to develop; adults live 4–8 months |
| Smokybrown Periplaneta fuliginosa | About 30 mm; shiny dark brown-black, fully winged | Damp, dark, poorly ventilated places: sheds, wall and roof voids, subfloors, mulch, drains and grease traps | Up to 17 egg cases of up to 26 eggs; 6–12 months to adulthood; adults live 6–12 months |
| Brownbanded Supella longipalpa | Small, 10–15 mm; pale glossy brown with very pale bands across the body | Indoors, in warm spots near the ceiling, behind wall hangings and loose wallpaper, in furniture and appliances | Only 2–4 months from nymph to adult; adults usually live 3–6 months |
| Oriental Blatta orientalis | Medium, 20–25 mm; evenly dark brown to black | Cool, damp places at or below ground: leaf litter, damp subfloors, around drains | Up to 14 egg cases of up to 16 eggs; 6–18 months to grow; adults live 3–6 months |
Despite its name, the German cockroach is Asian in origin: a 2024 genetic study of 281 cockroaches from 17 countries found it evolved from the Asian cockroach about 2,100 years ago, probably in human settlements in India or Myanmar.
The house in section, roof to drain
Put the table onto a drawing of a house and a pattern appears. The same department’s descriptions, sorted by where each species is found:
- Roof and wall voids
American and smokybrown cockroaches; the Australian cockroach sometimes comes in to these too.
- High in the rooms
Brownbanded cockroaches, whose egg cases are glued in higher and drier places than other cockroaches usually use.
- The kitchen
German cockroaches: under sinks, in and under cupboards and drawers, and around appliances such as refrigerators.
- Subfloor and drains
Oriental cockroaches, which keep at or below ground level, with American and smokybrown cockroaches around drains and grease traps.
- The garden
Australian cockroaches in shrubs, woodpiles, bark and leaf litter; smokybrown cockroaches in mulched areas.
The American cockroach prefers coastal areas, the department says, and lives indoors where the climate is cool and outdoors where it is warm.
The clues they leave
Cockroaches are mostly active at night, so the evidence is usually what they leave behind. When looking for German cockroaches, the department suggests a torch and a search for live or dead insects, small dried droppings, smears of droppings, cast skins and empty egg cases. The smears have a purpose: some species press their droppings onto surfaces, and the droppings carry a chemical signal that marks places to feed and gather.
The brownbanded cockroach breaks the night-time pattern: seeing one by day is not unusual. It leaves tiny dark droppings and cast skins on cabinets and shelves, and it is commonly carried into houses in furniture and luggage. For any species, sticky traps can be effective for watching numbers over a long time.
Why the species changes the treatment
The department’s descriptions show why the species comes first. A German cockroach infestation needs every crack, crevice, void and surface the insects travel over treated. The Australian cockroach, living mostly outside, may need treatment of garden beds against the house, woodpiles and mulch. The brownbanded often needs treatment through a whole building, with attention to furniture, cupboards and bookshelves.
Across all of them, the department says the trend is towards fewer sprays and more dusts and baits, because space sprays are unlikely to reach where cockroaches hide. Baits come as gels, pastes, particles or stations, and can offer safety advantages in commercial food areas, schools and hospitals. Sheet 04 covers what a café keeps on file about its pest control.
Surfaces where food is handled must not be treated, and cupboards and pantries should be emptied first, the department says. Chemicals must always be used as the label directs, and poor hygiene can limit how well they work.
Why they matter to health
The Better Health Channel says bacteria a cockroach swallows can live on in its gut for months, sometimes years, and leave in its droppings. Cockroaches also vomit and leave droppings on food, and it is thought disease may pass to people who eat food they have contaminated. They need a steady water supply to survive, which is why a dripping tap is worth fixing. Damp, which the smokybrown and oriental cockroaches seek out, is also what rot fungi need in timber: sheet 05 sets out the moisture band in which decay starts.