Ants use 'photo library' to find home

(Phys.org) —Ants keep a collection of 'snapshots' taken close to the nest so they can find their way home from unfamiliar locations.

This is the discovery of scientists at The Vision Centre (VC) and the Research School of Biology at the Australian National University, who found that Australian jack jumper ants, just by briefly scanning the panorama, can quickly determine where their nest is from 15 metres away, even from areas that they have never visited before.

"Jack jumper ants from each nest typically head towards a specific tree 6-15 metres away, which they climb to hunt for prey or harvest honeydew exuded by plant-sucking insects," says Dr Ajay Narendra of The VC and ANU.

"Ants typically use two navigational strategies to move between the nest and foraging sites. They rely on surrounding landmarks or path integration – keeping track of the distance and the direction that they've travelled on their foraging journey to compute the direct route home."

In the study, the researchers captured jack jumper ants at the base of their foraging trees and released them at unfamiliar locations 10 metres or more from the nest.

"We fed the ants with sugar water and provided them with prey to motivate them to go home," says Dr Jochen Zeil of the VC and ANU. "Once the ants reached the nest, the scientists captured them again and released them at points opposite to the first release sites.

"These ants actually reached their nest faster than when they were first released, which was surprising. As we captured these ants when they first reached the nest, they wouldn't have any path integration information because they've already used it to get home."

"So these ants would have been expecting to be at the nest, and since the nest isn't there, they should have been disoriented and started searching for the nest or for familiar landmarks," Dr Narendra says.

"But they didn't – they left the release sites, briefly scanned their surroundings, made a decision and headed in the right direction to the nest."

The researchers found that the ants returned faster because they only had landmarks to guide them home. "The first batch of ants reached home more slowly because they had both path integration and landmark information," Dr Narendra says.

"The path integrator told them to go the imagined route to where the nest should be, but what they saw from the landmarks urged them to go in the correct direction, and that created a conflict.

"On the other hand, when they were captured at their nest and released again in a different spot, they had no path integration information at all, so there was no confusion. They simply followed the information provided by the views they had learned close to the nest."

Dr Zeil says it's possible that these animals take snapshots of how the nest environment looks like from different directions when they first leave home. "It appears that they capture snapshots somewhere between one to five meters away from the nest, and store them in a small library of images.

"So when they're lost, they match these snapshots with what they see and through this comparison are able to determine the home direction. They don't need anything else – they can find themselves being transported to unfamiliar locations up to 15 metres away and still find their way home immediately.

"Previous research has shown that honeybees too return home from unfamiliar locations, which led to the conclusion that they use maps," Dr Narendra says. "Maps, however, are expensive to acquire and to store and our study reveals that all insects need are memorised scenes of their nest from different directions, which they can compare with their current view."

The study "Mapping the navigational knowledge of individually foraging ants, Myrmecia croslandi" by Ajay Narendra, Sarah Gourmaud and Jochen Zeil is published in the latest issue of Proceedings of The Royal Society B.