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Crayfish with a Compass

Virginia Tech

This next story comes from the weird world of animal science.  We know that birds, bees and whales use the electromagnetic fields of the Earth to guide their travels, but it turns out other animals also have that sense.

If you have a dog, you might have noticed that canines circle around or adjust their position before doing their business.  One study suggests they’re using the Earth’s magnetic field – preferring to excrete after aligning along the north-south axis.  Satellite photos show cattle also line-up that way. James Skelton, now at the University of Florida’s Forest Entymology Lab, found this ability in another animal as a graduate student at Virginia Tech.

“Crayfish actually have a compass, and it turns out they have a really good magnetic compass,” he says.

No one knows what causes dogs or cows to align themselves with electro-magnetic fields, but working with colleagues at Tech Skelton came up with an interesting clue in crayfish.  These mud dwellers are infested with tiny worms that keep them clean.

“They’re called branchiobdellidans," Skelton says, "but I like to just call them crayfish worms, because that’s a little easier.”

James Skelton (left) and the lead author of their study, Lukas Landler (right), at work on Sinking Creek near Blacksburg.
Credit Virginia Tech

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If too many worms take up residence, they’ll start messing with their host’s internal compass.

“Crayfish are pretty good at staying separated," he explains. "They each hide under a rock.  They’re very territorial.  But if the crayfish becomes disoriented, it’s plausible that they’re more likely to bump into other crayfish, and so these worms can possibly jump ship and escape high densities and competition.”

In other words, the worms might be hijacking the crayfish so they can escape to another animal that might offer a better supply of food.  The study appears in the latest edition of Scientific Reports.