Howler Monkey (IMAGE) University of Nebraska-Lincoln Caption In some areas of Costa Rica, howler monkeys like this one are infected with parasites once limited to capuchin and spider monkeys. After humans hunted capuchins and spider monkeys out of existence in the region, the parasites immediately switched to howler monkeys, where they persist today. Credit Photo courtesy Daniel Brooks Photography Usage Restrictions None 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.