The Natural History Museum of Denmark has studied the insect population on its rooftop for 18 years, tracking 1,543 species of moths and beetles and more than 250,000 individuals. In a study appearing in The Journal of Animal Ecology, museum researchers conclude that warming temperatures are affecting specialized insects that rely on a single food source. The nut weevil, for example, feeds only on hazelnuts; it appeared on the roof during the first half of the study but not the second. Scientists at the museum suspect that the nut weevil and other specialists are moving north, where the climate is cooler.