Each Jan. 1, UC Davis zoology professor and butterfly expert Art Shapiro resolves to find the first cabbage butterfly fluttering through the new year. For more than 20 years, the year's first butterfly has signaled a new cycle of research about how this immigrant insect has adapted to the highly variable climates of Northern California. In his search for the first, Shapiro recruits other butterfly collectors with an annual contest. The first person to bring in a live Peris rapae, with the exact time, date and place of capture, wins a pitcher of beer (or its cash equivalent if the lucky winner is younger than 21). The butterfly must have been found outdoors in Yolo, Solano or Sacramento counties. Since 1972, the first cabbage butterfly has appeared as early as Jan. 4 (1990) and as late as Feb. 26 (1987). Generally, the European native emerges each year following environmental cues, such as temperature, rain and length of daylight. Shapiro uses his accumulating data to predict the arrival of the first butterfly of the year, but he's willing to help others look for more obvious clues: a field full of flowering wild mustard, four days of afternoon temperatures exceeding 60 degrees Fahrenheit and lengthening daylight hours.