Most people think cockroaches are disgusting. And if you've ever turned on a kitchen light, to find them skittering for dark corners, you probably agree (reference: my first apartment). But are cockroaches actually dangerous? And how do I get rid of them?
How Many Kinds of Cockroaches Are There?
There are nearly 5,000 named species of cockroach around the world, with some experts estimating that there are another 5,000 species that have yet to be named, described and classified. Their classification is actually a point of contention - and I won't take a position on which suborder they're in, how many families they consist of, or whether they should, in fact, share the same order with termites (which some scientists argue would bring termites closer to their evolutionary origin as social cockroaches).
An estimated 60 to 70 species can be found in the continental United States (depending on who you ask), but most people are likely to interact with no more than a dozen of them - depending on where you live.
For example, if you live in a suburban home, near trees or areas with a lot of mulch, you may see the occasional "woods cockroach" - any of several species in the genus Parcoblatta that live in wooded areas and eat organic matter. Woods roaches are native to the Americas, tend to be fairly large (over one inch in length), and should not be a problem for homeowners.
While woods roaches may come into your house (e.g., inadvertently hitching a ride on some firewood, entering through soffit vents or other openings, or flying toward porch lights - only the males fly), they do not want to be there. And (good news!) woods roaches have not been known to reproduce indoors. So, if you see one, don't freak out. Woods roaches are actually very beneficial, consuming decaying matter in the leaf litter around trees and serving as a significant food source for other animals (including the red-cockaded woodpecker).
Woods roaches are different from wood-feeding cockroaches, which are in the genus Cryptocercus. Wood-feeding roaches are fairly uncommon, and in the U.S. they are found in the Appalachian region (including the mountains of North Carolina), and northwestern states - though some species are also found in parts of Asia and Europe. Wood-feeding roaches are similar to termites: they eat wood, form "families" with a pair of adults that rears broods of young and build galleries in decaying wood. Interesting, right?
While we're at it, let's tackle two other cockroach questions that come up a lot: Are palmetto bugs actually cockroaches? And what are "smoky browns"? Luckily, these questions have the same answer! Palmetto bugs, "water bugs," and smoky browns are all the same thing: a species of cockroach called Periplaneta fuliginosa. So, yes, palmetto bugs are roaches. (It's also worth noting that some folks call any brown cockroach a "smoky brown.")
Why Are There Cockroaches in My House?
But when most people think of roaches, they aren't thinking of these wild species. They're thinking of pests found in buildings, particularly in urban settings. There are four or five of these species in the U.S., of which the German cockroach (Blattella germanica) is most common.
German roaches are relatively small, rarely reaching more than half an inch in length. And they can't fly, so are often introduced into new places by humans - catching a ride in your groceries, cardboard boxes, etc. But once they're in, they can disperse rapidly. An infestation in one apartment can quickly spread throughout the building.
To a German roach, humans are a moveable feast. They'll eat almost any organic material. The crumbs in your cabinet, bits of food that slip down the crack by your stove, your garbage can - they're all smorgasbords to germanica.
In fact, the German cockroach is so well-adapted to life in buildings that scientists have not found wild populations of this species that are not associated with humans. So, the German cockroach has diverged (evolutionarily speaking) from the other 52 known Blattella species, all of which live outdoors.
How Fast Do Cockroaches Breed?
German roaches have a unique reproductive strategy among cockroaches. After mating, a female makes an egg case containing approximately 40 eggs. The case remains attached to the rear of the female's abdomen, where the embryos incubate for approximately three weeks before live young emerge. These nymphs are tiny - no more than 2 millimeters long - but begin foraging immediately. While her offspring develop within the egg case, the mother provides them with water, which is critical in the dry, air-conditioned buildings these cockroaches infest, and she protects them from predators.
The nymphs do not go through a pupal stage, but molt six times over the course of around 40 days before becoming adults. Once they reach the adult stage, they have wings (even though they can't fly) and are capable of reproducing.
Because adults can live for up to a year, reproduce repeatedly and can produce a new generation every 60 to 70 days, the introduction of a single mated female can create an infestation of thousands of roaches fairly quickly - a population of millions over the course of a year (under optimal conditions).
Are Cockroaches Dangerous?
While roaches do gross people out, there is little understanding of their role as a vector of disease. We know they carry various pathogens (such as harmful bacteria), but there has been little or no epidemiological research done that links roaches to outbreaks of human disease.
That said, cockroaches can exacerbate allergies and asthma. Proteins in the bodies of cockroaches are what sensitize people, especially children, and trigger allergic reactions, and those proteins can attach to dust particles and become airborne when roach feces dry up or when a cockroach dies and its body breaks down. This can be a serious problem in areas with large infestations, most commonly in urban, multi-family, low-income apartment buildings.
And roaches also contribute to indirect health effects stemming from the overuse of pesticides. So-called "bug bombs," for example, are not particularly effective - but can expose people to harmful amounts of insecticide. They aren't very effective because: A) they do not do a very good job of reaching into the nooks and crannies where roaches hide; and B) roaches have become highly resistant to these pesticides.
How Do I Get Rid of Cockroaches?
So, how can you effectively deal with a cockroach problem? Your best bet is an integrated approach:
- Improve sanitary conditions to reduce the amount of food available to roaches.
- Reduce clutter, so there are fewer places for roaches to hide and reproduce.
- Physically change your environment to limit the ways a roach can access your home. For example, use caulk to block cracks around electrical outlets and eliminate water leaks that give roaches access to the moisture they need.
- Use pesticide dusts (e.g., boric acid or diatomaceous earth) selectively, in hard-to-reach areas, such as behind cabinets or under the sink.
- Place insecticide baits in areas where you see cockroaches - but where children and pets cannot reach them. For example, behind the refrigerator.
Note: Many thanks to Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State, for taking the time to talk to me about cockroaches. Thanks also to Matt Bertone, the diagnostic entomologist with the NC State University Plant Disease and Insect Clinic, for the photo at the top of this post and insights regarding palmetto bugs/smoky browns. Any errors in the above post are mine alone.
