Daphnia (image) Virginia Institute of Marine Sciences Caption This is a female Daphnia magna with eggs. This is one of the species used in the study of bacterial hitchhikers. These aquatic animals are about the size of a flea. Credit Photo courtesy of Adam Petrusek. Usage Restrictions For one-time use to illustrate this press release. 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.