These things can really bug you. Scientific American

The German cockroaches plaguing your kitchen are mostly close relatives, a finding that could help scientists stop them from spreading disease.

Dogs may be man’s best friend, but we are the cockroach’s. A new study concludes that the ubiquitous German cockroach (the kind likely skittering across your sidewalk or kitchen last night) spreads most actively within apartment units and complexes, and that those roach populations have closely linked genetic structures. (Think of it as a culture that values intergenerational living.) Roach populations that have spread between one city and another or between continents, on the other hand, share a lot less DNA. 

That makes sense. But what's interesting is how the study relates to the way these guys travel. The flightless insects are so finely adapted to city life as to be virtually incapable of existing in any natural environment. So for a roach to get from Raleigh, North Carolina, to Gary, Indiana—or, heck, to Paris—it must do so through human means, hitching a ride in a car, on a ship, or on a plane. Roaches trek those great lengths less often and in lower numbers, and so tend to reproduce with partners with little genetic similarity when they arrive at their new homes. 

On the other hand, when they're spreading from the underside of your dishwasher down to your neighbor's place, they likely got there on their own six legs. Those more mobile roaches are probably close cousins, according to the study.    

Genetic differentiation among B. germanica populations at different spatial scales. 

This matters because these bugs can be vectors for pretty menacing bacteria, including E. coli and Salmonella. With a correlation between geography and genetics established, scientists can better identify where certain roach populations came from and what route they took, information which could then be used to curb waves of proliferating disease.  

The research might also support one reason cockroaches (and bedbugs, by the way) are such hardy invaders of the world's cities: inbreeding. Mating practices that can weaken human gene pools actually seem to strengthen those of these pests. One more reason they will probably outlast all of humanity.

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