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Know Your Enemy: Cockroaches

Few living things gross people out like the humble cockroach. But are they actually harmful? (Image courtesy of Clemson University-USDA Cooperative Extension Slide Series,

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 of the thousands of species out there, only a few can be considered pests.

There are well over 4,000 described (i.e., named) species of cockroach around the world, with some experts estimating that there are another 5,000 species that have yet to be classified by taxonomists. Their classification is actually a point of contention – and I won’t take a position on which suborder they’re in, or how many families they consist of.

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 they may come into your house (e.g., inadvertently hitching a ride on some firewood, or entering through soffit vents or other openings), they do not want to be there. And (good news!) they 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 are found only in the Appalachian region (including the mountains of North Carolina). 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? Not creepy at all.

But when most people think of roaches, they aren’t thinking of these wild species. They’re thinking of pests found 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.

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 eggs incubate for approximately three weeks before live young emerge. These nymphs are tiny – no more than 2 millimeters long – but begin foraging immediately.

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 fertilized female can create an infestation of thousands of roaches fairly quickly – a population of millions over the course of a year.

But 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 enterococci), but there has been little or no epidemiological study done that links roaches to human disease.

That said, cockroaches can exacerbate allergies and asthma. Proteins in the bodies of cockroaches are what 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, where children become sensitized to these allergens.

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.

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. E.g., 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. E.g., behind the refrigerator.

This is a lot of information, but we haven’t even touched on other pest species of roach, such as the American cockroach. If you’re interested, let me know and I’ll pull together another post on them.

Note: Many thanks to Dr. Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State, for taking the time to talk to me about cockroaches. Any errors in the above post are mine alone.