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Where There’s Heat, There Are Cockroaches

The views expressed are those of the author and are not necessarily those of Scientific American.


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The sticky Southern summer heat makes me slightly insane.  It’s an agitation that grows deep within me as the season ripens, and the humidity and temperature rise in equal fashion. This heat has been both a blessing and a curse throughout my life.  The giver of swims in the local creek and refreshing mint juleps is also the giver of 20-pound sweat drenched t-shirts and late summer landscapes browned and brittle as death itself. As Mrs. Pearson states it’s a “pregnant heat.” No doubt ready to burst forth with “lost dreams and wayward souls.”

This intense steamy heat, so taxing for me, is a dream for another wayward soul–the cockroach.  In North Carolina a single home can host an alarming variety of these heat-seeking insects. Brown-banded, German, American, Smokybrown, and Oriental—these enterprising pests with intercontinental names will turn any warm inviting home into a United Nations of roaches. It’s a terrifying thought—notoriously indestructible vermin that feed off hot, humid misery.

Blatella_germanica_(German_cockroach)

Blatella germanica (German cockroach)

Luckily roaches are not indestructible. You might expect a cockroach with a German moniker to enjoy the cold heartiness of tough Northern European stock. However, as it turns out, German cockroaches aren’t really German. They hail from the wet heat of Southeast Asia and while the jury’s still out on their ability to withstand nuclear proliferation, we’re positive they are quite fragile in the face of cold.  Cool and dry climates, anywhere too high in latitude or elevation, are uninhabitable for the German cockroach.  At the chilly temperature of 23˚F, 50% of German cockroaches die within 10 hours.  At 14˚F, 50% die within the first hour.

German cockroaches suffer for their evolutionary past.  Their ancient brethren originated and expanded 220 million years ago during the Carboniferous when the planet was on average 6-7˚ warmer than today.  This warm Earth produced a heyday for roaches and ultimately gave us the 3,500 species known today.  Paleontologists affectionately nicknamed this time period the Age of Cockroaches.

So in many aspects German cockroaches suffer from the genes of their long dead insect ancestors. Of course these same genes allow them to fare very well in the sultry summer heat of North Carolina.  Whereas the genes from my forefathers that produced my bald head are having quite the opposite effect.   Thus the roach’s genetic preference for warmth means it fares poorly in the cold outdoors.  Indeed, its life is intrinsically linked to mine, well, humans in general, and more specifically our temperature controlled homes.

Blatella germanica (German_cockroach)

Blatella germanica (German cockroach)

I don’t know much about roaches, professionally.  I’m a marine biologist.  I know them as well as any summer-sweat-drenched southern boy would. However, my time in New Mexico, seeing 2-inch American cockroaches in the thousands enjoy the warmth of the cement patio in the cool evening, drove home the linkage between roaches and heat.

Despite my lack of entomology credentials, I’ve been thinking a lot about roaches lately.  How are human homes and behaviors shaping their evolution?  Rob Dunn, Jon Eisen, Kerry Kinney and myself are holding a meeting in June at the National Evolutionary Synthesis Center to address (not just cockroaches, but) the full gamut of scenarios that have shaped the evolution of the biome that dwells inside our homes.

I digress. Let’s get back to the enterprising German cockroach, shall we? It seems their outlook for invading colder temperatures may not be so bleak after all.  (Sorry Minnesota, your safety is not guaranteed.)  First, populations of German cockroaches living in France more than 550 miles apart are not genetically different.  This means that these prolific little buggers possess an amazing ability to migrate and spread genes over very long distances. Second, this same study also shows a remarkable amount of genetic distance among German roaches within different habits of the city, i.e. bakeries versus homes. Third, German cockroaches are able to acclimate to colder temperatures.  Half of the roaches acclimated for two weeks at 50˚F were able to survive over 4 days, rather than just 10 hours, at 23˚F.  Outdoor strains of the German cockroach from a dump that wintered in a nearby field also faired better in colder temps than those dwelling in a warm bakery.

This ability to quickly adapt to new conditions and extensive migration have no doubt lead to great success for the German cockroach.  Our warm homes may provide oases allowing them to spread beyond their means.  Our homes–and bakeries–are evolutionary halfway houses to cooler pastures. As stated so well in this abstract, “we may conclude that the spreading of this animal will not soon come to an end.”

Images: EPA and Lmbuga.

Craig McClain About the Author: Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, created to facilitate broadly synthetic research to address fundamental questions in evolutionary science. He has conducted deep-sea research for 15 years and published over 40 papers in the area. He has participated in dozens of expeditions taking him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses mainly on marine systems and particularly the biology of body size, biodiversity, and energy flow. He focuses often on deep-sea systems as a natural test of the consequences of energy limitation on biological systems. He is the founder and chief editor of Deep-Sea News, a popular deep-sea themed blog, rated the number one ocean blog on the web and winner of numerous awards. Craig’s popular writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web. Follow on Twitter @DrCraigMc.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 4 Comments

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  1. 1. Postman1 2:21 pm 04/30/2013

    Ahhh… There is nothing else quite like the crunching sound made when you step on a two inch long roach on a cool terrazzo floor on your way to the bathroom at two AM. Followed quickly by the high pitched squeal, emitted involuntarily, and waking up your sleeping spouse and children. One of many reasons I left Florida and reside above 3000 ft altitude now. They infest the cleanest houses and businesses, now matter how often treated, and multiply at an amazing rate, and are thoroughly disgusting. Even the picture at the top this page makes my stomach quiver.

    Link to this
  2. 2. Postman1 2:24 pm 04/30/2013

    Quivering stomach causes typos ^.

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  3. 3. helenavargas 4:53 pm 04/30/2013

    So if I keep my house below 50F over winter, despite Southern Maryland summer, have I any hope of statistically lowering my risk of harboring (gulp) roaches? Or am I just acclimating them to stay alive but a tad less active? I keep looking for data on their lifetimes, but I really don’t want to read up on their reproductive prowess, for fear of, well, scaring myself silly.

    Actually, I saw more black widow spiders than roaches during my 15 years in New Mexico. Never minded the former.

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  4. 4. Bill_Crofut 5:39 pm 05/6/2013

    Re: “German cockroaches suffer for their evolutionary past. Their ancient brethren originated and expanded 220 million years ago during the Carboniferous…”

    Since cockroaches are identifiable as such in Carboniferous fossil form allegedly 220 million years of age, the “evolution” of the cockroach would seem to be non-existent.

    Link to this

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