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Where There's Heat, There Are Cockroaches

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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.

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

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