A climate's changes are tough to quantify. Butterflies can help. Entomologists prefer "junk species--" the kind of butterflies too common for most collections-- to keep up with what's going on in the insect's world. They're easy to find and observe. When do something unusual, something's changed in the area.Art Shapiro's team at UC Davis monitors ten local study sites, some since the 1970s. The ubiquitous species are the study's go-tos, helping distinguish between lasting changes (climate warming, habitat loss) and ones that will right themselves (one cold winter, droughts like last year's). Consistency is key; they collect details year after year, no empty data sets between.A few species have disappeared from parts of the study area altogether, probably a lasting change. On the other hand, seemingly big news in 2012 might be just a year's aberration. Two butterflies came back to the city of Davis last year, the umber skipper after 30 years, the woodland skipper after 20-- both likely a result of a dry winter with near-perfect breeding conditions of sunny afternoons and cool nights.