Air-sacs (IMAGE) University of British Columbia Caption The blue fluorescence of the air-sac was due to resilin—an almost a perfect rubber found in parts of insects where elasticity is key, as in the elastic energy that powers a flea’s incredible jump. Credit Philip Matthews Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.