With nothing but a featureless expanse of sand around them, Saharan desert ants can still figure out how far away from home they are using a sophisticated internal odometer, German scientists reported last week. Scientists knew the direction component of the ants’ navigation system relied on the sun, but they did not know how the ants figured out how far to go. A team led by neurobiologist Harald Wolf of the University of Ulm in Germany hypothesised that the ants essentially counted their steps. To test their theory, the researchers altered the length of the ants’ steps by giving them either stilts made from pig bristles or amputating the bottoms of their legs, leaving them with stumps. The theory was that with altered step sizes the ants with longer legs would go too far in looking for the nest, while the ants with shorter legs would not go far enough. The results, published in the journal Science, showed just that. Once they were accustomed to their new legs, the ants adjusted their calculations of how many steps it took to get home and behaved exactly like normal ants would. —LAT-WP

A little on the top, for environment’s sake

If you want a greener urban environment, start at the top. A cover of vegetation on the roof can help reduce energy bills and improve air quality. Green roofs have become popular in Europe, and they are beginning to catch on in North America. Some use ground-cover plants like sedum and other succulents while others are more like gardens, with shrubs and even trees. Green roofs can provide immediate benefits, but what about the long term? Scientists at the University of Toronto investigated the environmental impact of a green roof over the expected life of a building. They modelled the impact over 50 years on an eight-story apartment building, designed by Susana Saiz, an architect who is one of the researchers.

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