Some species of red wood ants, found in Europe and North America, build 7-foot mounds in the forests. A few years ago, a husband-and-wife team of geologists, Gabriele and Martin Berberich, noticed the mounds tend to be found near active tectonic faults. They struggled to publish that observation. "It sounds crazy, right? — geology and ants interacting?" says their collaborator Israel del Toro, an entomologist at Lawrence University in Wisconsin.

But in a study published last week, they outlined an experiment modeled on medicine's double-blind test to determine whether there is an association between the geology of a place and the occurrence of ants there. They found there is.

How they did it: Del Toro and his colleague mapped the location of nests in two forested areas in Denmark without knowing the geology or the hypothesis. The Berberichs meanwhile compiled data about the tectonic faults in the area, not knowing what Del Toro found.

When they put the two datasets together, they found the ants' nests "were eight times more likely to be found within 60 m of known tectonic faults than were random points in the same region but without nests."

What's next: Correlation, of course, doesn't imply causation. The researchers want to know whether there is any underlying biology. One idea: the ants could be using warm gas released from microfaults that can't be seen with the eye as chimneys to stay active during the cold winters. They plan to now map the microfaults in the area and determine their temperature.