Cockroaches at home: why bay leaves don't work and what actually gets rid of them

Cockroaches: why bay leaves don't work and what actually gets rid of them

The air duct is not the cockroaches' way in. Covering it is like putting a screen on the balcony and leaving the window open. If there are cockroaches in a tiny flat, with hardly any furniture or food, they didn't come from the street: they already live inside. That's the conclusion you reach when someone asks how to keep them out. The short answer: you don't keep them out, you keep them from staying. And for that you need to tell the species apart, because not all cockroaches behave the same way or are fought with the same methods.

German cockroach and black cockroach: not the same thing

The German cockroach is an internal breeding problem. It nests in warm, damp crevices: behind the fridge, in the motor, under the sink, behind loose skirting boards, inside the kitchen cupboard. It doesn't need you to lay out a buffet; it can live for two months on the grease around a seal. The black or oriental cockroach does climb up from drain pipes and sewers. It gets in through drains, dry traps and plumbing gaps. Confusing the two leads to buying the wrong product and repeating the infestation every summer.

Some people claim a robot vacuum can harbour a nest. It's not the typical spot, but it's not far-fetched either: it's a dark, warm box with dust, food scraps and a damp corner if it's kept in the kitchen or bathroom. For a German cockroach that's an apartment with central heating. The points to check are the brush and roller, the dust bin, the filter compartment and the motor cavity, and the charging dock, which gives off heat. The robot doesn't attract them; it's the dirt it picks up that does.

A dry trap is a motorway

The drain trap is the great unknown. Cockroaches roam freely through drain stacks, gullies and inspection chambers. The most common situation is that traps either don't exist because of shoddy building work, or they've dried out. A trap full of water is a barrier they can't get past. If it's dry, they come in through the sink or shower drain. You will never see them swimming in or diving up through a toilet.

The overflow hole in the sink is another route almost nobody looks at until they see it with their own eyes. Covering all the drains, sealing joints and pipe peine, and fitting grilles in kitchens and ground floors is the first line of defence. Without moisture or water they won't settle in. Bleach and thorough drying. And watch out for coffee machines: water, heat and darkness. In a hotel, by the third year they started appearing and settled into the coffee machine.

The colony lives in the building's drainage system

Fipronil or imidacloprid gel in joints and skirting boards kills the ones that cross it, not the colony. The colony lives in the building's drainage system, and neither the spray from Amazon nor sheer determination reaches it. What really works is covering all the drains, sealing joints and pipe peine, and accepting that if you have a plasterboard cavity, they breed in there: either you open it up or you live with the neighbourhood.

The line "if you take away their food they'll leave" is a myth. They can survive for weeks eating cellulose and their own droppings. Whoever said that has never had a serious infestation. Cleaning is essential because they leave pheromones: where one gets in, like ants, the rest trinc.

The bay leaf war: what the evidence says

Bay leaves, lavender and rosemary have fierce defenders. The claim is that their antennae are very sensitive to smells and they get disoriented. There's also bicarbonate of soda for cleaning the pheromones. And cleaning vinegar or turpentine, which supposedly kill them if a single drop touches them. Against that, the opposing stance is blunt: there is no evidence whatsoever that these grandma's remedies work, they have never worked. A creature that lives among faeces and in the sewer is not repelled by vinegar. Certain compounds not liking them doesn't solve the problem.

What does work are the chemicals specifically designed to kill them slowly, growth inhibitors and, as a last resort, physical or chemical barriers. Bayer Magnum is expensive but lasts for years and wipes them out completely. Gel from any other brand works if the enemy is already inside, alternating active ingredients to avoid creating tolerance or mutations.

Fumigate the whole building or move out

In a block of flats, getting rid of the cockroaches in your flat is pointless if the neighbour is a slob. They settle there first and then hop across to other apartments. You can eliminate them in yours but they'll come back. The solution being argued for is to include pest control as a regular cost in the homeowners' association, every month or every fortnight, without people complaining. Fumigate hard or die in the infestation or move far away.

Poison traps all over the house are another route, but they depend on the species. Not every trap works for the same species. Sometimes catching a couple of them is enough. And some people hear noises above the plasterboard: it's frightening what can be accumulating up there.

Why do they multiply in summer?

Moisture is what attracts them most. In summer, a basin left in the shower can end up with dozens of drowned cockroaches in it when you return from holiday. Heat speeds up their reproductive cycle and drives them out of their hiding places. The nymphs are completely white and photosensitive: as soon as they see light they come crawling out like worms, and that's when you can actually squash them. Once they mature and turn brown it gets harder. Males during breeding season are very agile and fast, very hard to catch, and they also have wings and can fly like a chicken.

Can you keep them out? You can make it harder. Door sweeps, window screens, grilles on overflows and plugs in place when drains aren't in use. Seal the hole where the meter cables come through with silicone. Replace the street door with a security door. And even then, if the building is infested, they'll come back. The question isn't how to keep them out, but how long it takes you to realise they're already inside.