To study the behavior of crab populations, scientists have developed a “robot-spy”. But everything did not go as planned.
His name is Wavy Dave, and it is a small robot in the shape of a crab, which reminds of a mixture between a children’s toy and a kitchen utensil. But Wavy Dave is much more than that: it is a biomimetic robot supposed to be able to imitate the behavior of the crabs to better approach and study them.
Its use is the subject of a study published in the journal Proceedings of the Royal Society On August 6, 2025, since researchers wanted to place it in situation and see how he influenced the group’s behavior, especially in a logic of seduction.
Dave and his big pliers
The authors write: ” Our goal was to mimic the behavior of a rival in a population of wild violinist crabs, and to know if other males were going to respond to this behavior. »
To do this, Wavy Dave did what any good male violinist crab made when he wants to attract the attention of a female: he agitated his big pliers. Indeed, the violinist crab, or Afruca Tangeri, owes his nickname to his enormous pliers, completely disproportionate to the rest of his body, which he agitates to attract females.
This gesture which, from a human point of view, resembles a harmless “hello”, is heavy with meaning in this species, since a very agitated pliers means that the male can fertilize the eggs of the female. Big pressure, therefore.
Wavy Dave wanted to pretend to be a competitor male, in order to see how others were going to react. Her pliers was scheduled to move like that of a real crab, and scientists controlled her remotely via Bluetooth. The theory was that the other males went to imitate him. Only, the females found this robot a bizarre air. Certainly a kind of Uncanny Valley of Crabs. And the others attacked him. In the end, poor Wavy Dave is doing with his broken clamp and the experience stopped prematurely.
Crabs attracted by competition
Despite everything, scientists managed to collect some precious data on the behavior of crabs, which we did not know exactly how they were going to react. Before the unfortunate fight, Wavy Dave was still able to show her pliers in the cantonade.
Previous work showed that the females were attracted in particular by the males who had the largest pliers, and which waved it the fastest. And in the presence of Wavy Dave, the other crabs tended to move their longer, but not necessarily faster.
In addition, they suspected the presence of females due to the behavior of Wavy Dave, and remained near him, but only started their “seduction dance” once they had clearly spotted a female nearby.
Experience also showed that crabs tended to be stimulated by this competition … but not at any cost. Thus, the males were less likely to return to their burrow while Wavy Dave was doing his number. Except when there was a crab with pliers larger than theirs.
Scientists summarize: ” Our study highlights the subtle ways whose invertebrates adjust their behavior to remain competitive in a dynamic environment. This means that Wavy Dave will be able to return to the field, once his pliers are repaired.
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