Fence Lizard (2 of 2) (IMAGE) Penn State Caption New research shows that when some fence lizards are attacked by fire ants they "stress out" with elevated levels of stress hormones -- a response that helps the species to flee quickly and survive. In contrast, the response to danger of fence-lizard populations that never have been attacked by fire ants is to freeze in place. The stress-hormone research, which is helping scientists to understand the impact of invasive species on native populations, was announced at the 2010 annual meeting of the Ecological Society of America by Tracy Langkilde, assistant professor of biology at Penn State University. This photo shows Dr. Langkilde holding a female fence lizard. Credit Langkilde laboratory, Penn State University Usage Restrictions The caption must be published along with the photo. License Licensed 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.