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Behold: The Cockroach Internet of Shit and Gut Bacteria

A new study tracks the sources of cockroach pheromones to, well, you know.
December 9, 2015, 2:45pm

Cockroaches are scientific wonders of horrible-ness. A cockroach, the result of a lineage spanning some 320 million years, is a well-oiled machine of pestilence, and some large part of this has to do with how it interacts with fellow cockroaches. Common "gregarious" varieties of these most crunchy of bugs excel at community.

Much of this socialization ability has to do with cockroach communication, which, according to a study out this week in the Proceedings of the National Academy of Sciences, is enabled by certain microbes that like to chill in the guts of cockroaches. That cockroaches can be attracted to each other's feces has been long-assumed, but the new research offers an interesting twist. The bugs aren't just into each other's poop, but are into the bacteria housed within that poop and, thus, the bacteria housed within each other's guts.


The researchers behind the current study, led by North Carolina State University entomologists Coby Schal and Ayako Wada-Katsumata, proposed a simple enough experiment to determine what if any role gut microbes play in feces-based communication among German cockroaches, which are usually regarded as worst of the bunch pest-wise. They would take some cockroaches and release them in a completely sterile environment, where the bugs would produce sterile or relatively sterile feces, while some other cockroaches would chill in cockroach-friendly filth, where they would presumably produce normal microbe-laden poop.

The ability of the German cockroach to infiltrate human environments, where it may spread allergens and pathogens in any number of ways, is mostly due to its collectivization ("aggregation," in the insect parlance) abilities. As a unified whole of gregarious cockroaches, the bugs see such benefits as "mate location, predator avoidance, thermoregulation, and prevention of water loss," as the study explains. Aggregation may also help cockroaches better forage in rapidly changing human environments.

It's no big secret that cockroach communities are functions of pheromones—chemical messengers that attract other cockroaches—but even among poop-delivered pheromones, researchers have much to debate. As the study notes, "identification of the fecal aggregation pheromones of cockroaches has been fraught with controversy." Even the basic chemistry of aggregation-driving pheromones has been in dispute.

"Some compounds are inconsistently detected in feces, and behavioral responses to them range from attraction to neutral to avoidance," Wada-Katsumata and Schal write. "More than 150 compounds, including 57 carboxylic acids, have been identified from feces of the German cockroach." It's these carboxylic acids, also known as VCAs, have seemed to be the most promising.

"We hypothesized that the fecal VCAs that mediate aggregation in the German cockroach originate from the bacterial community in the feces," they add, "and, because gut-associated bacteria are acquired from the environment, we posited that both the VCA profiles and the behavioral responses to them depend on environmental conditions."

What the entomologists found is that the cockroaches living in sterile conditions had many fewer VCAs in their poop, and also elicited much less aggregative behavior. Their conclusion is that VCAs are tied to gut bacteria and also act as a socialization stimulus. That the exact makeup of the cockroach VCAs depends on their specific environments can then account for the wide diversity of cockroach poop pheromones.

As May Berenbaum, an entomologist at the University of Illinois, Urbana-Champaign unaffiliated with the current study, told Science News, the cockroach shit internet is nothing less than "a beautiful story of biological cooperation." Amen.