Thorn close-up (IMAGE) Field Museum Caption Hollow thorn evolved for ants to take shelter in; in exchange, the ants protect the plant from attack. Credit (c) Field Museum, Corrie Moreau Usage Restrictions Please incude credit to (c) Field Museum, Corrie Moreau 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.