Blackflies + Mudsnails (IMAGE) Cary Institute of Ecosystem Studies Caption Blackflies have the highest mercury concentration among Grand Canyon invertebrates. As larvae (top), they are important fish prey. When blackflies emerge as adults, they transfer mercury to birds, bats, lizards, and spiders on land. New Zealand mudsnails (bottom) contain mercury but are indigestible to trout; when fish eat them, they pass through unscathed. When the snails die and decompose, the mercury they contain is released back into the river. Credit Credit: US Geological Survey/Freshwaters Illustrated-Dave Herasimtschuk Usage Restrictions May be used to promote this press release. 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.