Tarantulas measure distance with their lateral eyes

April 21 (UPI) -- The original tarantula species, Lycosa tarantula, sometimes called the tarantula wolf spider, has a knack for geometry.

The nocturnal species ambushes its prey from its camouflaged burrow. The technique is not all that unusual, but researchers at the Autonomous University of Madrid found the spider takes a unique route home after dispatching its prey.

The species doesn't retrace its steps. Instead, it calculates its two-dimensional movements as if they were the sides of a right-angle triangle. The hypotenuse of the hypothetical triangle guides the spider home.

As revealed in a new study, published this week in the Journal of Experimental Biology, the tarantula uses polarized light to track its movement away from its burrow and calculate its return trip.

"To calculate the distance it has traveled, the animal needs an odometer that registers the route, its location with respect to the finish point, which would be the burrow, and a 'compass' to track the direction of travel," lead researcher Joaquin Ortega Escobar, a neuroscientist at AUM and the Spanish Foundation for Science and Technology, said in a news release.

Polarized light serves as the spider's compass. Escobar and his colleagues determined the spider's median eyes measure the light's angle, while its anterior lateral eyes measure direction. The anterior lateral eyes -- with a little help from the posterior lateral eyes -- also determines distance.

"These eyes look at the substrate," Escobar said. "Seeing as they point downwards, it seems logical to think they would have a role in measuring the distance traveled."

When researchers covered the lateral eyes with water soluble paint, the spiders had trouble traveling the correct distance back to their burrows.

"When we uncovered them, they could return to their nests perfectly. They need the lateral anterior eyes to measure the distance," Escobar said.