Butterflies with speedier metabolisms may live longer. Kristjan Niitepold at Stanford University in California and Ilkka Hanski at the University of Helsinki measured the energy expenditure of Glanville fritillary butterflies (Melitaea cinxia, pictured) by placing them in chambers and recording their carbon dioxide output. Every few days, the butterflies were forced to fly in the chambers for 10-minute stretches. Butterflies with the highest rates of CO_2 production lived the longest. Field experiments in which butterflies were released and recaptured showed the same pattern. Peak metabolic rate during flight could explain up to 33% of lifespan variation.
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