Sewerology 101: How & Why Bugs, Rats, Snakes, and other Creepy Crawlies Get Into Homes & Businesses from the Sewer

This article by Jerry Cates, first published on 7 October 2015, was last revised on 8 August 2021. © Bugsinthenews Vol. 16:10(01):

Prepare Yourself for a Little TMI…

You know all you ever wanted to know about sewers already, right? The operative word is “want” to know. Hardly anybody wants to know more about the sewer. That may explain why plumbers make the big bucks. They “plumb the depths” of things nobody else wants to touch. To most, details about the sewer under their home or place of work is not just TMI, it’s way, way, way too much information.

But TMI can be translated another way: Too Much Ignorance. We’re mostly ignorant of the things we prefer not to think about. This article will delve into such stuff, but don’t stop reading. Ignorance can be dangerous. Trust us on this: you need to know more about your sewer. Not a whole lot more, maybe, but more. Sometimes a little bit of knowledge can save you a lot of grief. It may even save your life. This is one of those times.

There’s A Whole ‘Nuther World Down There…

Late instar American cockroach, whose favorite habitat is the sewer. This cockroach is known to carry a number of parasites and diseases of concern to humans and our companion pets.

Late instar American cockroach (Periplaneta americana), whose favorite habitat is the sewer. This cockroach is known to carry a number of parasites and diseases of concern to humans and our companion pets. Keep in mind that this insect begins as a tiny egg, hatching as a tiny white nymph. The nymph turns reddish-brown, then molts six to 14 times over — on average — a 600 day period (almost 20 months) before reaching adulthood with a body length from 1 3/8th inch to 2 1/8th inches (34-53 mm) long. Immediately after molting the insect is white in color, but it soon darkens. All stages of development actively forage for food.

Some naturally associate sewers with death, but in actuality they teem with life. Rats, water bugs (a euphemism for the peridomestic cockroaches known commonly as American cockroaches, and scientifically by the taxonomical name Periplaneta americana), snakes, and all kinds of other forms of wildlife.

If you were an American cockroach you would proudly boast that your genome happens to be the second largest insect genome on record, bested only by the migratory locust (Locusta migratoria), that your genome codes for 522 taste receptors (the largest of any other insect), plus 154 olfactory receptors, along with enlarged groups of genes coding for detoxification, immunity, growth, and reproduction. Then you’d probably smirk while pointing out that these genetic faculties help explain why your species of cockroach adapts so well to human-occupied ecosystems.

But then, you’re not a cockroach… Thank goodness…

Two Worlds, Inches Apart…

In this article we will be telling the tale of two worlds, the “world of the sewer” and “our world, up here.” In the process we will help the reader come to grips with the not too pleasant fact that though those two spheres seem eons apart, they are in truth separated by only a few inches — if that.

So, why should we care? Good question. Here’s the answer:

The few inches that separate our world from that of the sewer provide, in general, a formidable barrier, as long as we do our part to make sure that barrier is strong. Whenever we fail to keep that barrier intact, those two worlds are capable of coming together in ways that create havoc in ours, the world “up here.” Most people are unaware of the dangers of letting our guard, on the barrier between us and the sewer, down. This article will not only alert you to those dangers, it will show you how to help make sure your home and place of work are kept as safe as possible.

Sewers and the American Cockroach

You may have noticed, in that earlier description, that the American cockroach is a peridomestic insect. The adjective refers to an organism that lives in and around human habitations. Unlike the German cockroach (Blatella germanica), however, which is the cockroach most often associated with humans and which is capable of creating large colonies in our kitchens and bathrooms, the American cockroach prefers habitats that are much more humid, i.e., places like our sewer systems. Still, they are associated with humans because we produce waste products that help them thrive. The moist environs of our sewers are perfect for them, and that’s where you are likely to find hundreds, even thousands of these insects. The author has opened sewer manhole covers all over Texas, and almost never finds the walls of the sewers they cover free of American cockroaches. Some, more than not, are so black with them you cannot see the sewer walls on which they are running about…

Adult male American cockroach (Periplaneta americana). Note the pale margin around the shield behind the head. This distinguishes the American cockroach from the smoky brown cockroach (Periplaneta fuliginosa), which is uniformly dark brown and lives in the landscape rather than in the sewer.

Adult male American cockroach (Periplaneta americana). Note the pale, yellowish margin around the shield behind the head. This distinguishes the American cockroach from the smoky brown cockroach (Periplaneta fuliginosa), which is uniformly dark brown and lives in the landscape rather than in the sewer.

American cockroaches pose a public health problem because of their association with human waste and disease. Obviously, an organism that lives in sewers gets covered with the stuff sewers have running through them. If these organisms stayed in the sewer and didn’t venture out, we’d never have to worry about them.  Fortunately, most — including the American cockroach — prefer living in the sewer. Furthermore, our sewers and the plumbing connections between them and the world above are, for the most part, specially designed to keep sewer vermin inside the sewer, where they pose no immediate risk to humans. That’s good news.

The bad news is that when a locale gets hit with heavy rains, or when someone or something causes a section of sewer to fill up with noxious odors or chemicals that these roaches find repellant, they do everything they can to escape the sewer and come up to where we live and work. The result is mass migrations of these vermin from out of the sewers to the homes and businesses above.

More bad news: Once they get out of the sewer it can take a long time for them to go back in. Like weeks or months. And while “visiting” our world, the males and females mate, and two days later the females lay eggs, averaging one egg case of 16 eggs every month.

What’s worse? Gosh, can anything be worse? Unfortunately, yes… The eggs hatch in 6-8 weeks, and the hatchlings — who have never experienced life in the sewer — tend to complete their life cycles above ground, not far from the place where they hatched from the egg. These misplaced cockroaches reach adulthood, mate, and produce new young.

Here’s some slightly good news: Most likely, they tend not to live as long as their counterparts, who live in the sewers. Furthermore, they usually try to stay out of sight as much as possible, spending most of their lives in the crawlspaces, attics, and skins of the buildings they hatched in. But — more bad news — as the seasons change, and their chosen living spaces become less friendly or even uninhabitable due to temperatures that are too high or too low, when heavy rains flood where they are, or when extended dry periods threaten them with desiccation, they have to move to places where their presence is more visible. That’s when we see them, and often we think they’ve just arrived when they’ve been living there, out of sight, for months or years.

But Now, Let’s Return To The Sewer, Shall We?…

The design features of our sewer systems that try hard to keep sewer vermin where they belong are the result of hundreds of years of plumbing research and development. Yet, like most things in life, those design features are not static things that work without our assistance. To work right, they require us to keep our plumbing fixtures in good condition, and in some cases they also require us to carry out adjunctive constructs that were not applied when our homes or businesses were constructed. When we fail at that, sewer vermin easily get into our homes and businesses, and that’s very bad news.

Once out of the sewer and into our homes sewer vermin like the American cockroach are capable of contaminating everything they touch with whatever pathogens they may have picked up “down there.” By way of example, more than 22 species of pathogenic human bacteria, viruses, fungi, and protozoans, plus as many as five species of helminthic worms, have been isolated from American cockroaches. It goes without saying that you don’t want that stuff inside your home, on your foodstuffs, or on the packages, cans, and shelves in your pantry. This article has one goal: to show you and others how to make sure sewer vermin stay where they belong, so you don’t have to worry about the results of the contamination they are capable of spreading when they get out of their preferred habitat.

That Said, A Word of Caution is In Order…

Most homes and businesses presently host some American cockroaches in their outer skins, in their crawl spaces, and in their attics. If they are not being seen, it’s because they are not being forced out of those spaces by weather conditions. If they are commonly visible or sporadically so, seasonal weather conditions are usually to blame. When you happen to see a few all at once, they didn’t just now arrive from “somewhere else.” They’ve been “here” all along, just out of sight.

My point is that the eradication of these pests is not a one-time, all-out, “nuke-’em with all you’ve got” kind of operation. You can nuke and nuke and nuke, and not see much improvement, mostly because their eggs are hidden out of sight, and a much larger number of mating, egg-laying adults are also still present in places no pesticides can reach, also out of sight. Yes, it may be possible to flood a home or business with so many broad-band pesticides that nothing that crawls will survive. Many pest control companies advocate just that kind of solution to an infestation of American cockroaches. We advocate against it, because we know from our 40+ years of experience in this field that such approaches always end up creating more pests than they eradicate, and — what’s even worse — expose the humans and their companion pets who live and work there to toxins that are unhealthy.

What’s The First Step?

The first step in getting rid of these roaches is to stop them from invading from the sewer, so no new ones are coming in from that source no matter what happens in the sewer. Then, with targeted applications of very specific pesticides, the adults and immature nymphs you cannot yet see (but that visit your living and working spaces unseen, in the dark and in places hidden from sight such as behind stoves, washing machines, and refrigerators) can be slowly, but surely eradicated.

I repeat: Ridding your home or business of American cockroaches is not something that takes place overnight.

Sewers and Rats, etc.

Besides American cockroaches, rats, snakes, and a number of other organisms live in the sewers and can enter your home via that route if you put out the welcome mat. The trick is to put up a No Trespassing sign instead.

So, How Can We Keep Sewer Vermin Where They Belong?

We’ll get to that in a moment, but first you need to know more about how your sewer connections are constructed.

Unless you live in a locale that has no running water, your home has several sewer appliances. These are the sinks, tubs, showers, and commodes that use plumbing to convey water and “stuff” from your home to a nearby sewer or septic tank. If the plumbing in your home is designed and installed properly, and if all your sewer appliances are used regularly (e.g., at least once a week) they automatically produce and maintain a hydraulic air-seal between each appliance and the sewer or septic tank into which the contents of each appliance flows. This hydraulic air-seal consists of a water-filled section of plumbing that completely occludes the plumbing pathway from the appliance to the sewer.

Not to Mention Your Roof Vents…

Now, there is also a vent pipe, past the hydraulic air-seal, that connects each sewer appliance drain to the sewer and to the roof of your home and/or business. Typically, that vent pipe is not screened where it projects above the roof. We are not quite sure why this is not done, but we suspect it just adds cost to the construction for something nobody knows enough to complain about. We’re complaining, but we’re a lone voice in the wilderness where this is concerned. More about that later…

But, Back to the Hydraulic Air-seals…

That occluded section of plumbing prevents sewer gasses and most sewer vermin from passing from the sewer into your home. How? By requiring sewer vermin to first take a swim, through several inches of water-filled plumbing, in order to bridge the gap between the sewer and the sink, tub, shower, or commode.

Usually, that works to keep sewer vermin out of your home. Though there are exceptions, it almost always works well, as long as the hydraulic air-seal is fully intact and functional. However, it doesn’t work at all if any of the sewer appliances in your home go unused for long periods. Often, in as short a span as two weeks, the hydraulic air-seals associated with unused sinks, tubs, and showers dry out, removing the occlusion between them and the sewer. When that happens, the sewer vermin have a straight shot into your home from the sewer, and some — the American cockroach in particular — are quick to take advantage of that.

So, just make sure your sewer seals are intact, and that every sewer appliance under your control is always kept fully hydrated. Sounds simple enough, right? And it is. In general. But, again like lots of things in life, the devil is in the details. Some of the details pertinent to the question at hand are less than intuitive. This article is devoted to making those details easier to understand.

The S-trap

The main connection between your sewer appliances and the sewer is a just a pipe. Fairly small pipes (often 1-1.5 inches in diameter) convey stuff, generally in liquid or semi-liquid form, from your sewer appliances to a larger pipe (often 4-6 inches in diameter) that connects your home to the sewer main or to the septic tank. At each sewer appliance the small pipe from that appliance emerges from the appliance as a straight pipe, but not for long.

A short distance from where the drains emerge from your sewer appliances the straight pipe is connected to a contraption that produces the hydraulic air-seal between the appliance and the sewer or septic tank. Many different designs have been patented for this contraption, but the first one — known as the S-trap — was invented by Alexander Cumming in 1775. Cumming’s invention became the motive force behind what eventually became the modern flush toilet. His main concern was to prevent sewer gas and other noxious smells from coming up from the sewer into the house. Before his S-trap was placed in use, the smells emanating from the home’s toilet were similar to those typical to a common out-house.

S-traps similar to the one invented by Alexander Cumming are still in use, in some locales, today. The basic design is a a section of pipe curved into the shape of the letter S, hence its name. The pipe draining the sewer appliance empties into a pipe curved like an S, then is connected to another straight pipe that continues downward to the sewer.

The Improved P-trap

Unfortunately, S-traps have one major disability. If too much water is drained through them at once, they will be siphoned dry in the process. Because this can cause the S-trap to fail, improvements were needed. The P-trap was invented to reduce that likelihood, and is the most common trap used in the United States today. S-traps, by comparison, have mostly gone by the wayside in the U.S. as they are not in conformity with most plumbing codes. They can still be found in some locations, however.

The P-trap is similar to an S-trap but has two features absent in the S-trap. The first is the addition of a horizontal section of pipe where the trap terminates. Instead of immediately draining downward, fluids exiting the trap have to flow horizontally for a short distance to reduce the risk the flow will siphon fluids out of the trap. The second feature found with the P-trap is the addition of a vent pipe where the horizontal pipe terminates at a juncture that takes the flow back down to the sewer. This vent pipe, which usually extends upward far enough to exit through the roof, makes it easier for an air gap to form in the stream, breaking the stream so siphoning is even less likely. The vent pipe also equalizes the pressure within the home’s plumbing system so flows through one trap won’t affect the level of the hydraulic air-seals in all the other traps in the house.

OK, So How Can You Keep Your Sewer Connections Sealed Against Sewer Vermin?

The most obvious answer is to use your sinks, tubs, showers and clothes washers often enough — at least once a week — that their P-traps are always loaded with water. That sounds easy, and if you use all those appliances regularly, it is. What if you don’t, though? Empty nesters who use only one or two bathrooms, leaving one or more unused for extended periods of time, often see more than their share of American cockroaches as a result. So do those who use the shower every day, but never take a bath, so the tub’s P-trap soon becomes dry as a bone.

For sewer appliances that never get used, the short answer is to turn on the spigot for a minute or so once a week to keep the P-trap sealed. A better answer, for some, is to pour 8 ounces of food-grade mineral oil down that drain, so you don’t have to remember to hydrate it every week. Just remember to do it again, with fresh mineral oil, every time you use that appliance, like when you have visitors who stay the night and use that usually unused bathroom.

If you own a business, like a restaurant, with floor drains, putting 8 ounces of food-grade mineral oil down each drain weekly is a good idea even if the drains are connected to appliances that are supposed to keep them wet. Often, those connections are faulty, especially if the store is more than 5 years old. The mineral oil will restore functionality to the drain’s trap.

Don’t Forget the Roof Vents…

But what about that vent pipe that connects to each P-trap? If sewer vermin run up that pipe from the sewer to the roof, they don’t have to go through a trap to exit the sewer. Then, once on the roof, they can get into your home or business through a myriad of gaps in the building. For that reason we believe all roof vents from the sewer should be screened.

More to come…


— Questions? Comments? Corrections? e-mail

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