Small, flat, and wily, cockroaches are expert opportunists that – without certain simple precautions – can invade our spaces quickly. But where do roaches come from and how are they getting in?
Let’s shrink down to their size for a minute, see how they’re sneaking in, and learn how to stop them at the door.
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The Two Types of Invaders: Roaches that Come from Outside, and Roaches that Come from Other People’s Stuff.
To get a handle on this vexing little origin story (that dates back more than 320 million years), it helps to understand that roaches come in two distinct varieties: Outdoor roaches, and indoor roaches.
The two types of roaches not only have different habitats, lifestyles, and adaptations, but use different modes of entry to invade and inhabit your home or business.
Where Outdoor Roaches Come From
The Main Invaders: American cockroach, Oriental cockroach, Wood cockroach, and increasingly the Turkestan cockroach.
Outdoor roaches live everywhere outdoors that have the conditions to support them: food, shelter, warmth, and generally, darkness and lots and lots of water. That means otherwise healthy habitats like mulch, hollow tree trunks, log piles, and decaying ground cover… but also unhealthy ones like garbage heaps and sewers.
When they decide to leave those outdoor spaces, there are a number of ways they get inside:
The ground around your house
These bugs are made for walkin’. The life of a cockroach is a life spent crawling through dirt, grass and mulch.
Even if your house is surrounded by urban concrete, roaches have no problems living in alleyways and around dumpsters. These species of roaches hide and hang out on the ground right around your home. It’s almost inevitable that they’ll find a way in.
How they get in: A roach’s shape and size are perfect for squeezing through tiny holes and slim crevices in the foundation or walls of a house.
You might forget that, besides the cracks from normal wear and tear, there are holes in the walls of your home that were put there on purpose. Important piping and wiring has to pass through somehow! Dryer vents and bathroom vents could let cockroaches and other critters inside if they’re not covered.
Pest control tip: You can fill cracks and crevices with steel wool. Then, apply caulk or spackle over the steel wool to seal the hole against water, dirt and roaches. Cover any vents with screens.
Nearby trees and shrubbery
We humans lament the fact that food doesn’t just fall from the sky. Well, for outdoor cockroaches, it does! Fallen leaves are their bread and butter outdoors, so it’s no surprise they love to live around trees and shrubs. Anything that brings them closer to the outside of your house also brings them closer to the inside.
How they get in: While every type of cockroach is capable of crawling in, several types can fly! That means they not only sneak in at ground level, but at eye level, and from areas as high up as your roof.
Loose weatherstripping or warped concrete can create gaps under a door that cockroaches can sneak through at night.
Window air conditioning units can create a similar problem—those side panels often leave tiny spaces around the window frame (foam, steel wool or even a rag can help with this). And even thin gaps beneath shingles can give them access to your attic.
Pest control tip: Always cover doors and windows with screens if you plan to keep them open, especially at night. Most cockroaches are nocturnal and some are attracted to lights, so the nighttime is when they’ll be most active and most likely to fly in toward your lights. Use a door sweep, draft stopper or weatherstripping to stop bugs from crawling underneath.
Truly the most revolting roach haunt: like horror movie monsters these bugs emerge from the dark sewers to crawl into homes and homeowners’ nightmares. They pick up dangerous bacteria from the sewage they’ve fed on and walked through and track it across every surface they touch.
How they get in: Once a roach has crawled out of the sewer, it’s already looking for a better place to hide. Cockroaches prefer dark, humid conditions with lots to eat, so if it thinks your house looks appealing, you bet it’s going to look for cracks or holes to climb through.
Pest control tip: Store your garbage can away from your house, if possible. (That goes for your compost heap, too!) Also make sure you’ve closed up any holes and cleaned the dead leaves from your gutters.
Where Indoor Roaches Come From
The Main Invaders: German cockroach, and brown-banded cockroach.
It’s easy to think about cockroaches invading from outside sources, but they often come from other people’s spaces and things.
Indoor, or “domestic roaches,” like the German cockroach prefer to live indoors. And they infest lots of human structures, not just houses. Unfortunately, these includes places you regularly bring things back from. And when you do, there’s a chance you could be bringing back roaches, too.
Where did roaches come from the last time you brought them in? Here are some of the places and things that might have given them their start:
2nd hand shops, hand-me-downs, and yard sales
“Another man’s treasure” isn’t the only thing hidden at yard sales and 2nd hand shops. All of those cardboard boxes that have been stored away for years are perfect habitats (and breeding grounds) for cockroaches.
How they get in: All it takes is to bring home one box of old magazines that’s also hiding some baby cockroaches for an infestation to spring up out of nowhere.
Pest control tip: Be very careful when buying things used, especially if those things come in old boxes or bags. You’re better off emptying them outside before you bring anything in.
Groceries and deliveries
Up next in the saga “Where Roaches Come From, Things You’d Rather Not Think About”—roaches living in grocery stores. At one store in Oregon, an inspector found “about 40 dead cockroaches” along the walls in the bakery section.
How they get in: It’s gross but they’re there, all right– and sometimes they hide out in the grocery bags and boxes you bring home or the containers you store food in. That could lead to an infestation in your car, too!
Pest control tip: Inspect your grocery bags before you move them from the cart to your car. Always make sure you open packages carefully, too. A warehouse full of cardboard boxes is prime roach country.
Indoor roaches can hitch a ride in your clothes
While I’m wearing them?! It’s rare but… yes. A cockroach could slip into the pocket of a coat as you sit or even climb into trouser cuffs. Roaches can also hide in purses, backpacks and shoes once you’ve set them down.
These bugs like worn, dirty clothes because of the smell of oils and skin particles that get stuck on them (not to mention the crumbs). Not only do dirty clothes attract indoor roaches (some roaches actually lay their eggs in them) but they can also be the reason they get into your house in the first place.
How they get in: If you’re not careful, a roach or two could hop into your basket at the laundromat and ride all the way home with you. If you visit another person’s house and they have an infestation, a cockroach can hide and become a stowaway in your coat or bag.
Pest control tip: Don’t leave your laundry bag or basket at a laundromat for longer than it needs to be there. Shake it out before you put your clothes back in, too. Shake out coats, bags and shoes if you think you might’ve been in a place with cockroaches.
How Both Types of Roaches Make Their Way In
Here’s another one you probably don’t want to think about: cockroaches can enter buildings and move from room to room through the pipes.
That’s how they infest apartment buildings so quickly. Seeing one cockroach in the bathroom might seem like nothing but it could be a sign of many more hiding elsewhere.
Pest control tip: The simplest solution to this potential problem is to use covers on your bathtub and sink drains that have holes that roaches can’t fit through.
Why Are Cockroaches Trying to Get In, Anyway?
A roach infestation almost always comes down to two things: cockroach’s need for food and water, and oftentimes a third—warm areas like those inside your home. Roaches don’t need much to survive but they’re always on the hunt for their next meal.
To prevent cockroaches from even noticing your house, you have to know what attracts roaches and eliminate those things (like crumbs or dirty dishes). Then, you can use your new knowledge of how they get in to keep them out.
Where do cockroaches come from? From anywhere and everywhere that sufficiently meets their needs—and if you let them, they’ll make your home one of those places, too.
With the information in this article, our other guides to cockroach behavior, and a little determination, you can seal off your home from cockroaches, get rid of them if you need to. And never have to worry about them invading your life again.
Written by Andrew Martin. Reviewed by Rae Osborn, PhD.
Andrew writes for, and along with his daughter, publishes Cockroach Facts. You can read more about him here.
Rae Osborn, PhD.
Dr. Rae Osborn holds Honors Bachelor of Science degrees in Zoology and Entomology, and a Master of Science in Entomology from the University of Natal in South Africa. She holds a PhD in Quantitative Biology from the University of Texas at Arlington, where her research was in Entomology. You can learn more about our contributors here.
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- Rodriguez, Amy. What Kind of Mulch Has a Problem with Roaches? SFGate Home Guides. Retrieved from https://homeguides.sfgate.com/kind-mulch-problem-roaches–79886.html
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