In neotropical forests, adults of many large scarab beetle species spend most of their time inside the floral chambers of heat-producing flowers, where they feed and mate throughout the night and rest during the following day, before briefly flying to another flower. Here we measure floral temperatures in Philodendron solimoesense (Araceae) in French Guiana and the respiration rates of Cyclocephala colasi beetles at floral and ambient temperatures, and show that the the beetles' extra energy requirements for activity are 2.0–4.8 times greater outside the flower than inside it. This finding indicates that heat produced by the flower constitutes an important energy reward to pollinators, allowing them to feed and mate at a fraction of the energy cost that would be required outside the flower. ; Roger S. Seymour, Craig R. White and Marc Gibernau