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Cockroaches Can Make Group Decisions.

Cockroaches Can Make Group Decisions.

Can cockroaches make group decisions? Today we’ll take a look at three scientific experiments that indicate that they can make simple, collective decisions.

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Cockroaches: Evolutionary Superstars

Cockroaches may be despised by most humans, but they are considered to be a prodigy of evolutionary design. A recent article in Forbes lists several amazing facts about cockroaches:

  1. Cockroaches have been found in diverse environments ranging from the arctic cold to the arid desert.
  2. Roaches can endure a month without food and more than two weeks without water.
  3. Cockroaches have two brains: one in their skull and another near their abdomen.

Over the last decade, scientists have found that the cockroach is a much more social creature than originally thought. For example, a 2012 BBC article reports that cockroaches can organize in equal, yet rudimentary, social groups based on very simple democratic customs. The commentary also states that roaches suffer when isolated, live together in generational family groups, and are capable of identifying related clan members.

“When they encounter each other they recognize if they belong to the same colony thanks to their antennae that are ‘nooses’, that is, sophisticated olfactory organs that are very sensitive,” said Dr. José Halloy, a scientist at the Free University of Brussels in Belgium.

Cockroaches Make Group Decisions

In 2006, Dr. Halloy co-authored research on cockroaches which appeared in a scientific journal entitled Proceeding of the National Academy of Sciences. His study showed that cockroaches regulate themselves through simple democratic decisions when attempting to seek shelter. In the experiment, 50 cockroaches were put in a dish that contained three shelters. Each shelter had the capacity to hold 40 roaches. In this scenario, the group of insects would always split themselves in half with two groups of approximately 25 insects hiding under two of the shelters while the third was left unoccupied.

In another part of the experiment, shelters able to contain all 50 cockroaches were placed in the dish. With this scenario, all 50 of the bugs would gather under a lone structure.

The full experiment can be examined here.

Followup Experiment

In 2007, Dr. Halloy performed a followup experiment that was published in a peer-reviewed journal called Science. Going with the hypothesis that cockroaches collectively follow two simple cognitive rules (they gather in the darkest spots with the most other cockroaches), Halloy and his colleagues attempted to trick the insects into doing something unnatural. Engineers were employed to build matchbox-sized robotic cockroaches that looked and chemically smelled like the real thing, at least enough to trick other roaches. These robots were programmed to act like cockroaches with similar preferences for darkness and crowds.

The robots were integrated with real cockroaches into a dish containing two shelters. One shelter was dark while the other was brighter. At first the robots and roaches would all gather under the darker shelter, but researchers eventually reprogrammed the robot roaches to gather under the lighter shelter. Subsequently, the real cockroaches all began to gather under the lighter shelter with the robots. Because this went against the roach’s cognitive preference for darkness, the scientists saw this as proof that the insects were making a simple collective decision to take shelter with other roaches under a less-dark shelter.

The followup experiment was covered by Time magazine and NPR.

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Another Interesting Cockroach Experiment

A 2010 BBC article covered an experiment which suggested that cockroaches also make collective decisions about food sources using a form of chemical communication. The experiment was carried out at Queen Mary, University of London by Dr. Mathieu Lihoreau, and the results were published in the journal Behavioral Ecology and Sociobiology.

“We released them into a small arena where there were two identical food sources. If they didn’t communicate, we would expect that they should just distribute on the two food sources equally,” said Dr. Lihoreau. Results showed that the majority of the insects fed on one food source until it was depleted. The scientists hypothesized that cockroaches use chemicals called cuticular hydrocarbons to communicate simple messages about identity, food, and shelter.

February 2015 Update: Cockroaches Have Personalities

In early February of 2015, The Daily Mail reported that a new science experiment showed evidence that cockroaches had primordial personalities. The study took place at the Université libre de Bruxelles, and results of the experiment appeared in a peer-reviewed science journal called Proceedings of the Royal Society B. By tracking 304 cockroaches using radio tags in a controlled environment, researchers were able to observe social behaviors in individual insects as they sought shelter and food sources.

One of the researchers involved in the study, Isaac Planas Sitjà, explained the primary personality characteristics that were observed:

We have categorized the observed personalities. We call them “shy or cautious” and “bold or explorers”… Shy individuals are those that spend more time sheltered and explore less the arena or the surroundings…. Instead, bold individuals are those that spend most part of the time exploring the surroundings and spend less time sheltered.”

Ultimately, the researchers concluded that the individual personalities of cockroaches influenced group decisions: “…these individual personalities have an impact both on the group personality and sheltering dynamics… Some groups quickly reach a consensus and make a collective decision, while other groups with conflicting personalities take longer to make a collective decision.”

Bottom Line

Cockroaches are very socially oriented insects. Several science experiments appear to show that they are capable of making very simple group decisions regarding food and shelter. These decisions are thought to be communicated through chemical cues. In February 2015, new studies have revealed that cockroaches have basic personalities that can have an influence on collective group decisions.

Updated February 17, 2015
Originally published July 2014

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