Pea crabs tickle shellfish to find love

Chuck Bednar for redOrbit.com – @BednarChuck

Using infrared cameras to capture the mating rituals of the New Zealand pea crab, researchers from the University of Auckland discovered that the male member of the species engages in an unusual behavior to gain access to females – tickling.

As detailed in a recent edition of the journal Parasite, the researchers observed the crabs (which live along inside shellfish) leave the safety of their homes and find a nearby mussel containing a potential mate. Once they find her, likely by following chemical signals, they spend nearly four hours trying to tickle their way in to get to her, National Geographic explained.

This marks the first time that this type of behavior has been found in a crustacean, co-author Oliver Trottier told the website. He and his colleagues are not yet certain why it works, but one possibility is that the male crab tickles the shellfish to relax it, so that it doesn’t force itself shut and crush him as he is attempting to reach the female.

Late night tickling (wink)

If the male pea crabs “keep rubbing [the mussel] in the same place until it goes numb,” there is a chance that they can sneak their way inside without being detected, he told Nat Geo via email. It could also help explain why the males are active during the nighttime, since the mussels are not as sensitive then (for reasons that have not yet fully been explained).

While crabs “can be crushed” by mussel anytime during the day, Trottier explained, it is far less likely to happen during the night, as the creatures are “hypersensitive” during the day. Also, male pea crabs are easy targets for potential predators if spotted outside the protective confines of their homes during daylight hours, he added.

Scientists have long wondered just how female pea crabs are fertilized, added Martin Thiel, who is a marine biologist at the Catholic University of the North in Coquimbo, Chile. They suspected that males went out hunting for females due to the fact that they are smaller and thinner, but this new research is the first to demonstrate exactly how the process takes place.

Once the males found a mussel that contained a potential mate, they never left it, Trottier and co-author Andrew G. Jeffs (also from the University of Auckland) wrote in their study. They added, “a pheromone-based mate location system is likely used” by the pea crab “to greatly reduce the risks associated with the location of females.”

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