Published online 15 November 2007 | Nature | doi:10.1038/news.2007.252

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Mechanical pied pipers for cockroaches

Insects can be lured into a shelter by scented robo-roaches.

Follow me: robots and cockroaches influence each others' behaviour.J. Halloy

Scientists have designed tiny robots that can mingle with a social group of cockroaches and influence their behaviour.

They say that similar robots will help them to unpick the decision-making processes in other gregarious species that carry out 'collective behaviours' such as deciding where to rest or selecting food sources. The researchers report their studies in today’s Science1.

Unlike ants and bees, cockroaches do not have a sophisticated social structure, but they do take notice of what their fellows are doing. Last year José Halloy, a theoretical biologist at the Free University of Brussels, Belgium, reported that when cockroaches have a choice of two or more shelters under which to settle, their decision is influenced by the number of cockroaches already there2.

In that study, the researchers placed up to a hundred cockroaches in an arena and found they were more likely to stop at one shelter if another cockroach was already there — and highly likely to stop if several were there. This accelerating pace of social gathering stopped sharply when the shelter became full — the cockroaches sensed the overcrowding and scurried elsewhere (similar to how tourists might behave when selecting which restaurant to eat at on a busy street). The scientists deduced the straightforward, but non-linear, mathematical relationship influencing an individual cockroach’s decision to follow or deviate from its general inclination to shelter in the dark.

Lured inside

For the new study, Halloy commissioned colleagues at the Swiss Federal Institute of Technology in Lausanne, Switzerland, to make cockroach-size robots based on this algorithm. His team built a simple one-metre diameter plastic arena containing two 155-centimetre diameter shelters, like beach umbrellas, for a series of trials on a community of four robots and 12 cockroaches. One shelter was darker than the other.

First they had to make the robots — which the cockroaches initially ignored or avoided — accepted members of the cockroach community. Because the insects recognize each other through the pheromones they release, the scientists collected the odorous chemicals from males and wrapped the robots in blotting paper containing a drop equivalent to the scent of one cockroach. So treated, they were accepted as fellow insects.

“They are very kind, not aggressive and they don’t bite. They are just a bit disgusting.”

José Halloy

Cockroaches are nocturnal and so always prefer to rest in the dark, a tactic that keeps them out the way of predators such as humans. When the robots were programmed to have the same preference for darker corners, the real insects congregated in the dark shelter in three-quarters of the trials.

But when the robots were programmed to prefer light places, the insects congregated in the lighter shelter in about 60% of trials. The presence of just a few robots with contrary 'instincts' was enough to override the natural preferences of cockroaches, notes Halloy.

He adds that the robots were also occasionally led by the real insects: about 40% of the time they found themselves in a place they were programmed not to like the light conditions of, since they too were inclined to join popular shelters. "The robots and the cockroaches were influencing each other," Halloy says (see video).

Social studies

“We are starting to realise how much social interaction there is among insects and this study shows that robotics can help us understand them better,” comments Roland Strauss, an insect biologist from the University of Mainz in Germany, who has developed robot fruitflies for his research on neuronal control of movement.

But before anyone gets ideas that group behaviour of troublesome insects such as swarming locusts might be diverted by a few judiciously designed robo-insects, Halloy cautions that robotic technologies are not advanced enough to make such real-world applications possible in the foreseeable future. Even using cockroach-scented decoys to lure insects into a trap wouldn't work, since live insects would notice if the other insects inside a shelter were dead.

Halloy has nothing — much — against cockroaches. "They are very kind, not aggressive and they don’t bite. They are just a bit disgusting," he says.

He is nevertheless moving on to work on chickens, another gregarious species that displays collective behaviours. The robotics required for this more complex species will have to be more sophisticated, he admits. He plans to get his future robo-chickens accepted by the brood by exploiting maternal imprinting, a phenomenon whereby a newly hatched chick will follow the first moving object it sees. Usually that is its mother, but it will settle for a robot if that's all that circumstances allow. 

  • References

    1. Halloy, J, et al. Science 318, 1155-1158 (2007). doi:10.1126/science.1144259 | Article |
    2. Amé, J.- M., Halloy, J., Rivault, C., Detrain, C. & Deneubourg, J. L. Proc. Natl Acad. Sci. USA 103, 5835-5840 (2006). doi:10.1073/pnas.0507877103 | Article | PubMed |
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