You open the door of a ground-floor bathroom or a basement in the morning and find a glossy black insect crawling slowly across the tiles, then slipping into the floor drain. It does not dash off like the small roaches, and it does not seem very bothered by the light. It is most likely the oriental cockroach (Blatta orientalis), also called the black cockroach or sewer cockroach.
This species lives on dampness, cool conditions and filth, and it enters the home through pipes and sewers rather than through doors. In this article we explain how to recognize it, why random spraying does not work against it, and where to place baits to end the problem.
Appearance: A large, glossy roach, black to dark brown, slow-moving, known as the sewer or water cockroach.
Habitat: It lives in cool, damp places such as sewers, basements, crawl spaces under buildings and around water drains.
Entry: It slips into the home through drain openings and cracks near the floor, and it does not climb smooth surfaces easily.
Life cycle: Its life cycle is slow and stretches over months, so it multiplies more slowly than the German cockroach, but removing it takes patience.
Rule: Fix the source of moisture and cover drain openings with a suitable cover. Prevention works better than spraying after they appear.
How to Identify the Oriental Cockroach
It is one of the easiest species to tell apart, because its color and movement differ from the other household roaches.
- Size: about 25 mm, roughly an inch, and it is broader and heavier than the German cockroach.
- Color: dark brown to black, with a light oily sheen.
- Wings: the male has wings covering about three quarters of the abdomen, while the female has short wing stubs that do not function. Neither can fly.
- Movement: slow and heavy, and you often see it sitting still near a drain or under the sink.
- Odor: you may notice a strong musty smell when numbers build up.
To tell it apart from the large reddish-brown American cockroach, see our article on the American cockroach. The black insect that sometimes resembles it is the cricket, which is an entirely different insect.
Where It Lives and Why You Find It Near Drains
The oriental cockroach prefers a cool, damp, dark environment, which is why it is common wherever water and decaying organic matter collect.
- Basements and ground floors: especially around floor drains and pipe leaks.
- Sewers and drains: it moves through them between buildings and climbs up into bathrooms.
- Under sinks and toilets: around the openings where pipes pass through.
- Outdoors: in fallen leaves, covered soil, stone walls and trash bins.
- Dry spells: it may move indoors in search of moisture when conditions outside become very dry.
Although it rarely climbs walls or reaches the upper floors, it can come up through pipes into upper-floor apartments in some buildings. It feeds mainly on food scraps and starchy foods.
Its Slow Life Cycle
What sets it apart is its slow growth. An infestation builds up slowly, but it stays for a long time if it is not treated.
- Egg case: dark brown and holding about 16 eggs. The female carries it for roughly thirty hours, then leaves it in a hidden spot near food.
- Number of cases: a female lays about eight cases in her lifetime.
- Hatching: about two months at room temperature, and longer in cool conditions.
- Nymphs: they molt seven times or more and need one to two years to mature, depending on temperature.
- Adult: lives a few months, and adults usually appear in large numbers in late spring and summer.
The small egg cases stick to surfaces and are not destroyed by spraying, so treatment needs follow-up for at least a month after the last sighting. You can see what they look like in our article on cockroach eggs.
Is It Dangerous?
The oriental cockroach lives in sewers and then walks into your kitchen, and that is exactly what makes it a health nuisance. It carries on its body and legs whatever it picked up in filthy places.
- Food contamination: it walks over surfaces, utensils and uncovered food.
- Allergies: its droppings and shed skins contain allergens, like those of other cockroaches.
- Odor: large numbers leave a musty smell, especially in basements.
For more detail, see the harm cockroaches cause and the diseases they carry.
How Do We Get Rid of It? Follow the Path It Enters By
The most common mistake is spraying the floor everywhere. The oriental cockroach does not live on the floor alone, but in the voids between pipes and walls, so we have to reach those areas.
- Dry things out: repair every leak or condensation point around pipes and drain openings.
- Clean up the source: remove leaf litter and accumulated trash around the house and under the garden, and keep bins closed.
- Seal entry points: use sealant around pipes, under doors and between the tiles and the wall.
- Apply gel: near the sources and in the cracks around pipes and drains, in small separate spots.
- Treat the voids: a dry powder can be dusted carefully into pipe voids and cracks, away from food, children and pets.
- Monitor: with sticky traps near drain openings to confirm the activity has stopped.
Note that indoor residual spraying and fogger sprays can scatter cockroaches instead of eliminating them. Read the general plan in getting rid of cockroaches for good.
Products We Recommend for the Oriental Cockroach
Because this species is large and takes more bait, at Orkida Agri we place more bait points per square meter than we do for the German cockroach, and we concentrate on the perimeter of drains and pipes:
- Max Force Forte Cockroach Gel 30 g: a fipronil gel for oriental and American cockroaches, used at the label dose, with emphasis around pipes and drains.
- Max Force Activ Cockroach Gel 30 g: a clothianidin gel that stays put on vertical surfaces and does not run in the heat, suitable for cracks behind toilets and under sinks.
- Advion Cockroach Gel 30 g: an indoxacarb 0.6% gel that we rotate to after a few weeks to vary the active ingredient and reduce the chance of resistance.
- K-Othrine 0.05 DP Powder for Cockroaches, Ants and Scorpions 1 kg: a deltamethrin 0.05% powder ready for dry dusting into pipe voids and cracks, used in specific enclosed areas and away from surfaces that get touched.
- Professional Cockroach Control Package for American Cockroaches at Home: a package designed for large cockroaches, suited to detached houses and their basements.
You will find the rest of our gels in the Cockroach Gel section.
Frequently Asked Questions
Can the oriental cockroach fly?
No. The male has relatively short wings and does not use them to fly, and the female has no functional wings at all.
Why does it show up in the bathroom after rain?
Heavy rain floods sewers and basements, so the cockroach comes out looking for a dry place, and it may enter through a drain opening or from under the door.
Is it enough to pour insecticide down the drains?
No. Cleaning the pipes and treating the area around them with gel works better than pouring liquids down the drain, because cockroaches move through voids that the liquid never reaches.
Is it the same as the American cockroach?
No. The American cockroach is larger and reddish-brown and sometimes flies, while the oriental cockroach is glossy black, slower and does not fly.
Do pepper or vinegar work to repel it?
They may confuse its senses for a short time, but they do not cure an infestation. What works is reducing moisture, sealing entry points and placing bait gel.
How long does it take for the infestation to end?
Usually one to two months, because its eggs hatch slowly and need follow-up.
Image source: Alvesgaspar — Wikimedia Commons (CC BY-SA 4.0)